A Treatise on Baking

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Temperature and Humidity

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Chapter XII

TEMPERATURE AND HUMIDITY

TEMPERATURE AND HUMIDITY

I. THE IMPORTANCE OF TEMPERATURE AND HUMIDITY IN THE BAKERY

The proper maintenance and regulation of temperature and humidity in the manufacture of baked goods is one of the most important problems in connection with the successful and efficient production of bakery products. The effect of temperature and humidity on dough fermentation and conditioning is explained in Chapter XI.

Quality ingredients and careful handling of the same throughout the various stages of bread making will not result in uniform quality baked goods unless the dough temperature and the temperature and humidity of the bakery are satisfactorily regulated. Adequate control of these factors means the reduction of fermentation and evaporation losses and the maximum yield of the best quality bread from the process employed. The maintenance of such control, therefore, is a wise economy.

Many modern bakeries have installed special automatic air conditioning equipment whereby the air in the bakery is maintained at certain definite temperatures and humidity. In such cases the worry of the baker concerning the control of these two factors is largely eliminated inasmuch as he “manufactures his own weather” and standardizes the atmospheric temperature and humidity throughout the bakery.

However, in those bakeries which do not have such automatic equipment, every precaution should be taken to secure the desired temperature and humidity by means of proper insulation of dough rooms, and adequate arrangements for heating, cooling and ventilation as well as some provision for the production of the necessary humidity. Improved equipment for supplying the desired humidity in such case’s has proven of considerable help. A description of such equipment is described later on in this chapter.

In every bakery today the constant use of the thermometer, hygrometer and other necessary instruments for the satisfactory measurement of temperature and humidity is strongly recommended.

In view of the important part which temperature and humidity have in the successful operation of any bakery, it is very essential that every baker should understand in a general way the following points:

1. What is meant by temperature and humidity.
2. How temperature and humidity are measured.
3. The effect of temperature and humidity on the fermentation and conditioning of doughs.
4. The proper dough temperature to be maintained. How secured and calculated.
5. The proper temperature and humidity to be maintained in the various parts of the bakery. How secured and how controlled.

The following paragraphs contain a detailed description of these points:

II. TEMPERATURE AND HEAT

A. EXPLANATION

In simple words temperature may be considered as the degree of “hotness” or “coolness” of any substance or body. In the language of the scientist, temperature is said to be the measure of the intensity of heat. The important point to keep in mind is that temperature and heat are not the same thing. Heat is merely one familiar form of energy and temperature is merely the measure of its intensity.

B. MAINTENANCE AND CONTROL OF TEMPERATURE

While heat may be generated or produced in several ways only three are of primary interest to the baker, namely:—

1. The natural heat of the sun, evidenced by the atmospheric temperature which changes with the seasons and climates.
2. Production of heat by the burning of fuel.
3. Production of heat from electricity.

Heat may be absorbed and the temperature lowered by means of refrigeration such as mechanical refrigeration or by the use of ice and cold water.

In order that the temperatures in a bakery may be controlled as desired and not governed by changeable weather temperatures, the installation of adequate heating and cooling devices are necessary as well as proper building construction, insulation and ventilation.

III. MEASUREMENT OF HEAT AND TEMPERATURE

A. HEAT

1. The British Thermal Unit

In measuring the amount of heat used according to the British System, a unit termed a British Thermal unit or so called B.T.U., is used. This is the amount of heat which is required to raise the temperature of 1 pound of water 1 degree F. One B.T.U. is equivalent to one quarter of one large Calorie.

2. The Calorie

The unit of measuring the amount of heat according to the metric system is either the small calorie or the large Calorie. The small calorie, often spelled with a small “c,” is the amount of heat necessary to raise the temperature of 1 gram of water one degree Centigrade. The large Calorie, usually spelled with a capital letter “C,” is the amount of heat necessary to raise the temperature of one kilogram (1000 grams) of water 1 degree Centigrade. Naturally one large Calorie is equal to 1000 small calories. One large Calorie is equivalent to about 4 B.T.U.’s or approximately the amount of heat required to raise the temperature of one pint of water 4 degrees Fahrenheit.

B. TEMPERATURE

1. Fahrenheit and Centigrade Scales

The Measurement of temperature is expressed in terms of degrees. According to the Fahrenheit system, 32 degrees F. indicates the temperature at which ice melts, and 212 degrees F. is the temperature at which water boils under standard conditions. Temperatures between these points are indicated accordingly.

According to the Centigrade (or Celsius) system, the freezing point of water is indicated as 0 degrees C. and the boiling point 100 degrees C.

This may be better understood by the following comparison of the two scales shown on the opposite page.

2. Conversion of Temperature Measurement From One Scale to the Other

(a) CONVERSION OF FAHRENHEIT DEGREES TO CENTIGRADE

If for any reason it is desired to express a Fahrenheit temperature reading in terms of the Centigrade system, the following calculation is necessary:—

Subtract 32 from the Fahrenheit reading. Multiply this result by 5/9. This will give the temperature expressed in the Centigrade system.

Example:— Suppose it is desired to express 77 degrees F. in terms of degrees Centigrade—

(b) CONVERSION OF CENTIGRADE DEGREES TO FAHRENHEIT

In order to convert a Centigrade temperature reading into the Fahrenheit scale the following calculation is necessary:—

Multiply the Centigrade reading by 9/5. Add 32 to this result in order to secure the equivalent temperature according to the Fahrenheit system.

Example:— Suppose it is desired to express 25 degrees C. in terms of degrees Fahrenheit,—

IV. MEANS OF MEASURING OF TEMPERATURE

A. NECESSITY OF THE USE OF TEMPERATURE MEASURING INSTRUMENTS

The natural sense of touch enables us to tell whether any substance is hotter or cooler than our own body temperature. However, the sense of touch is very unreliable and gives us only a very crude indication of temperature. For instance after eating ice cream, cold water may no longer feel cold. If a person is not feeling well or has a slight fever, his sense of temperature is greatly distorted. Some bakers honestly believe that they can tell the temperature of a dough by its feel to the hand. No matter how well trained one may be this cannot be done with any degree of certainty and such practice is indeed dangerous in the production of bakery products where temperature plays such an important part.

COMPARISON OF FAHRENHEIT AND CENTIGRADE TEMPERATURE SCALES

Actual temperature measuring instruments such as the mercury thermometer, the pyrometer and electrical thermometer are the only safe and reliable means of obtaining actual temperatures.

Every bakery, large or small, should be equipped with such instruments of precision in order to eliminate all guess work concerning temperatures and to avoid the evil results which are bound to follow poor regulation and control of temperature. Therefore, it is highly important for every baker to become familiar with the use of these temperature measuring instruments and the principle on which they operate. The word thermometer—means instrument for measuring temperatures. There are several different instruments for doing this, such as the ordinary mercury thermometer, the pyrometer often spoken of as a thermostat, and the electric thermometer which is often termed a thermo-couple or electrical pyrometer.

B. MERCURY THERMOMETER

1. Construction and Operation

The ordinary mercury thermometer is perhaps the best known instrument for measuring temperature. The operation of a mercury thermometer is based on the fact that mercury or quicksilver expands when heated and contracts when cooled to a much greater extent than glass. The amount of this expansion or contraction of mercury corresponds to the change in temperature and therefore may be used to indicate the existing temperature at any time.

A simple mercury thermometer consists of a heavy glass tube of very narrow bore and has a bulb at one end containing mercury. The other end of the tube is sealed tightly. The thermometer tube is so graduated or marked that it will indicate correctly the prevailing temperature to which the thermometer is exposed. For instance, if the thermometer is placed in hot water the heat causes the mercury contained in the thermometer bulb to expand materially. It therefore rises in the tube and in a short time the mercury column reaches a fixed height. The reading opposite the top of the mercury column indicates the temperature of the water. If the thermometer is placed in a vessel containing cool water the mercury contracts and drops to a lower point in the tube. The extent to which the mercury rises and falls is dependent oh the temperature to which the thermometer is subjected.

If the bulb of a mercury thermometer is completely immersed in a vessel containing shaved ice which is partially melted, the mercury column recedes until the melting point of ice is reached. This point is 32° F. or 0° C. and will remain constant as long as the thermometer bulb is kept in the ice water provided the water does not absorb more heat from its surroundings than the ice will absorb in melting. If the bulb of the thermometer is immersed in a vessel of water which is heated until it boils, the mercury will be expanded by the heat and will rise in thermometer tube until it reaches the boiling point of water (212° F. or 100° C. at standard barometric pressure). As long as the water is kept boiling, this temperature reading on the thermometer will remain constant inasmuch as when water boils, its temperature does not increase any further. Various types of mercury thermometers are made depending on the purpose to which they are to be put. Thus we have indoor and outdoor atmospheric thermometers, dough thermometers, oven thermometers, as well as those designed for use in cruller frying, tempering tanks, etc. The range of the thermometer readings as well as the general construction of the thermometer should conform to the purpose for which it is to be used. All of these different kinds of thermometers should be constructed so that the mercury bulb and tube will be protected against breakage.

Mercury thermometers can be constructed covering ranges in temperatures between 38 degrees below zero Fahrenheit and about 900° above zero Fahrenheit.

2. Calibration or Checking op Mercury Thermometer

The baker is especially fortunate today in being able to secure high grade thermometers which are guaranteed to read correctly and which will maintain their accuracy indefinitely provided ordinary care is exercised in handling and using them.

This high degree of perfection now available in thermometers is due to the scientific care and skill employed by the modern manufacturer of such instruments. In the making of these thermometers,—specially selected and treated glass is used and each thermometer is properly and sufficiently aged before being graduated.

In studying the subject of mercury thermometers one often reads about the “calibration” of thermometers. This means the checking up of the accuracy of the reading of the thermometer at different points along its scale. This is done by tying the thermometer to be calibrated alongside of a standardized thermometer which has been tested by the U. S. Bureau of Standards,—and then immersing both in a vessel of water which has been brought to a definite temperature in the neighborhood of that for which the thermometer being calibrated, is to be used.

The readings on the both thermometers should be carefully noted at the same time. Thus the necessary correction to be applied to the unstandardized thermometer can be observed and should be recorded. In like manner, the thermometer being checked can be tested at various points along the scale. The melting point of ice (32° F.) is obtained by the use of a vessel of shaved ice, partially melted. This vessel should-be adequately insulated so that the water will not take up more heat from its surroundings than the ice will absorb in melting.

The calibration of thermometers requires considerable care and skill and is a job which should only be done in a laboratory equipped for such work by a person trained in this sort of work. After the necessary corrections are observed at certain points along the thermometer scale, a calibration curve can be drawn which will indicate the corrections to be applied at temperatures between these points, provided the bore of the thermometer is uniform.

The accuracy of a thermometer which is not guaranteed at the time of its purchase should be calibrated before using.

If the scale on any thermometer is found to read incorrectly it does not mean that it will have to be discarded, but merely that the necessary corrections should be applied in reading the same.

However, if successive calibration tests show that the corrections first determined have changed noticeably through usage of the thermometer, it indicates that the accuracy of the instrument in question may continue to change as time goes on. Hence, for real accurate temperature reading, the advisability of securing thermometers of high quality becomes apparent in order that the necessity for repeated calibration may be avoided. Much time and trouble is saved by purchasing only dependable thermometers whose accuracy is guaranteed by the manufacturers.

C. METALLIC EXPANSION THERMOMETER

This instrument is usually used for high temperature measurements such as in the case of bakery ovens. It is sometimes spoken of as a pyrometer.

Its operation is based on the principle that metals will expand with heat, but that the amount of expansion of different metals subjected to the same temperature change may be different. If two strips of such unlike metals are riveted together with one end rigidly attached to an immovable base and the other end left free,—the strip made up of the two metals will curl in one direction if the temperature is increased but will curl in the opposite direction if the temperature is decreased.

Now by attaching a pointer to the free end of this strip of metals and so arranging the device that the pointer will move over a suitable graduated scale, the temperature to which this strip of metals is subjected will be indicated. The metallic expansion thermometer is usually much slower in showing the existing temperature than either the mercury thermometer or electric pyrometer.

D. ELECTRIC PYROMETER

This instrument is sometimes called an electric thermometer but is different from either the mercury thermometer or the metallic expansion thermometer in its mode of operation.

The electric pyrometer is generally used for high temperature measurement such as that of the oven. The manner in which one familiar

type of electric pyrometer operates is as follows:—The ends of two wires of’ especially selected different kinds of metals such as chromium and nickel are twisted and welded together forming what is known as a “hot junction.” The two free ends of the wires constitute the “cold junction.” When the hot junction is heated, a very delicate electro-motive force or millivoltage is created which varies in its strength with the difference in the temperature of the hot junction and that of the cold junction. Thus if the hot junction is inserted in the oven and the free ends (cold junction) outside of the oven are connected to a very sensitive instrument known as a millivoltmeter especially designed to register the delicate electromotive force, an increase in temperature is shown by a higher reading on the scale of this instrument and a lower reading is indicated when the temperature is reduced. This scale is graduated so as to read directly in terms of degrees of temperature. The thermo-couple or twisted ends of the two dissimilar metals may be placed in any one particular spot in the oven, but the millivoltmeter and indicating dial may be placed in some convenient location outside of the oven. The electric thermometer is very accurate.

V. RECORDING TEMPERATURE INSTRUMENTS

In order to secure a permanent record of the temperature of any particular location, room, proof-box or oven, recording devices have been constructed in connection with various types of temperature indicating instruments. These recording attachments usually consist of a chart which is gradually moved by clock work and a pen point which is attached to the temperature indicating needle. This pen point rests on the moving chart and in this way marks down the temperature in the form of a line. Thus, at the end of the day there will be a complete record on the chart of the temperature at all times during the day. Such recording devices are used to very good advantage in the modern bakery, and are generally termed Recording Thermometers.

VI. TEMPERATURE REGULATING DEVICES-THERMOSTATS

As previously stated in those bakeries which are equipped with air conditioning outfits where air is circulated through the dough room, makeup room or proof-box at the desired

temperature and humidity,—the problem of maintaining the proper atmospheric conditions in the bakery is considerably simplified. However, in cases where there is no such equipment, it is practically impossible to control the temperature of different parts of the bakery by hand adjustment of radiators, steam valves, refrigerating systems, ventilation, etc. Temperature regulating devices are available for doing this automatically. Such regulators are often spoken of as thermostats.

A thermostat is so constructed that when a certain temperature is reached,—it will operate a device which automatically shuts off or reduces the source of heat, and when the temperature falls below a certain desired temperature, turns on or increases the heat supply. In this way, a practically constant temperature will be secured automatically.

VII. HUMIDITY

A. EXPLANATION

Roughly speaking, humidity means the “wetness” of the atmosphere, or in other words the amount of moisture or water vapor contained in the air. It is a well known fact that on some days the air is drier or less humid than on other days.

B. THE DEFINITION AND MEASUREMENT OF RELATIVE HUMIDITY

Relative humidity means the relative amount of moisture contained in air at a definite temperature in comparison with the amount of water vapor which air at that temperature is capable of holding.

Relative humidity is expressed in terms of percentage. All air naturally available under ordinary conditions contains some moisture, but let us suppose, for the sake of example, that we did have air at a certain temperature which contained no moisture at all. This air would have a relative humidity of 0%. If, however, this air at the same temperature were saturated with all the water vapor it could hold, then it would have a relative humidity of 100%. If this air were to contain 70% of the maximum amount of all the moisture it could possibly hold at this temperature, it would have a relative humidity of 70%. The higher the temperature the greater the amount of water vapor which can be held by the air. Thus, hot air can hold much more moisture than cooler air, and in the summer time, the air is often more humid than in the winter time. If air with fairly high relative humidity were chilled it would soon have a relative humidity of 100% and then drops of water would begin to separate out in the form of a “dew.”

C. MAINTENANCE AND CONTROL OF RELATIVE HUMIDITY

The maintenance and control of humidity in all parts of the bakery, dough room, proof box, oven, etc., is of utmost importance in the efficient production of quality bakery products. The proper humidity in different sections of the bakery may be secured by the use of automatic air conditioning equipment as previously explained. In cases where such equipment is not installed, various humidifying devices may be employed. Such humidifiers can be purchased to meet the needs of the baker, or simple devices may be improvised by the baker to introduce moisture into the air, thus increasing the relative humidity.

While such home made equipment is not as satisfactory as specially constructed equipment, it often assists materially in securing the humidity desired.

The proper humidity in the proof box may be secured by the use of air conditioning equipment or by the introduction of wet steam at low pressure. The desired humidity in the oven is secured by means of low pressure steam. This subject is discussed in greater detail in this chapter under special headings.

VIII. MEANS OF MEASURING RELATIVE HUMIDITY

The percentage relative humidity in the storage room, dough room, proof box or other sections of the bakery is measured by an instrument known as a hygrometer.

There are two different types of such instruments which may be used in the bakery.

A. WET AND DRY BULB THERMOMETER

The principle on which the wet and dry bulb thermometer operates so as to indicate the relative humidity of the atmosphere is based on the fact that when water or any liquid evaporates it has a cooling effect,—and that the faster this evaporation takes place, the greater the cooling effect. This point may be illustrated by wetting the hand with water and then fanning the moistened surface so that the water will evaporate or dry quickly. Everyone is familiar with the cooling sensation produced. The wet and dry bulb thermometer arrangement merely consists of two thermometers identically alike, mounted close together on wooden frame or support. The mercury bulb of one of these thermometers is left exposed to the air. This is called the “Dry Bulb” thermometer. The mercury bulb of the other thermometer is tightly covered with a wick or cloth, the other end of which extends into a small vessel or tube of water. Thus the water seeps up through the wick and the mercury bulb is thus surrounded by a thin layer of water and is therefore always wet.

Hence this is called the “wet bulb” thermometer. Naturally due to the cooling effect of the evaporation of the water this thermometer will ordinarily read lower than the dry bulb thermometer. However, the difference in the readings of these two thermometers at any one time, depends on the rate of the evaporation of the water surrounding the mercury bulb of the wet bulb thermometer. Now, inasmuch as water evaporates slower in very humid air than it does in drier air, we can easily see that there will be less evaporation of the water in the wick where the relative humidity is high than when it is low. Consequently, the lower the relative humidity the greater will be the difference between the readings on the wet and dry bulb thermometers, and vice versa. If for instance, the air is saturated with moisture or in other words, if the relative humidity is 100%, then there would be no difference at all between the readings of the two thermometers.

In using the wet and dry bulb thermometer arrangement it is necessary that an adequate supply of clean distilled water be kept in the water reservoir at all times so that the wick will always be thoroughly wet. Frequent replacement of used wicks by new ones is advisable. Naturally, the entire wick must be kept clean and free from dirt or anything which would interfere with the free seepage of water through it. Furthermore, it is advisable to fan the wet bulb thermometer slightly before making the actual temperature readings.

The actual difference in temperatures noted is an indication of the percentage or degree of the relative humidity of the atmosphere at the time and place the readings are made. By referring to a chart which may be secured from the U. S. Weather Bureau,—the actual relative humidity may be secured. Such charts are usually supplied with wet and dry bulb thermometers when purchased.

At ordinary barometric pressure the following chart will give the baker the necessary data covering the range of relative humidities ordinarily encountered in the different sections of the bakery. In using such a chart proceed as follows:

1. Note the room temperature by reading the dry bulb thermometer.
2. At the same time read the wet bulb thermometer.
3. Then refer to the Relative Humidity Table, locating the reading in the left hand vertical column which corresponds to the existing room temperature.
4. Then follow this line over horizontally until it meets the column headed by the number of degrees representing the depression on the wet bulb thermometer (or in other words the difference between the readings of the dry and wet bulb thermometers). The number thus located represents the existing percentage relative humidity.

Note: Relative Humidity tables prepared by the U. S. Weather Bureau will show dry bulb thermometer readings 1° or 2° F. apart. The chart shown herein is considerably abbreviated, only showing temperatures 5° apart. However, for intermediate temperature readings the percentage relative humidity can be estimated very easily.

Example: Suppose the reading on the dry bulb thermometer is 80° and the corresponding reading on the wet bulb thermometer is 72°. The difference between these readings is 8° and the existing relative humidity is therefore QS%.

Relative Humidity Table

Percentage Relative Humidity Shown Above

B. THE HYGRODEIK

The hygrodeik is a special form of wet and dry thermometer which is so arranged that reference to the relative humidity tables is not necessary. The hygrodeik is constructed with a certain chart placed between the two thermometers. This chart is so drawn that curved lines start from all points on each thermometer. Whenever it is desired to ascertain the

percentage relative humidity the small sliding pointer is moved to the scale at the left and set at the temperature on the scale corresponding to the reading of the “wet-bulb thermometer.” The index arm of the instrument is then swung to the right until the pointer meets the curved line originating from the degree on the right hand scale corresponding to the reading of the “dry bulb thermometer.” When the sliding pointer is directly over the intersection of these two curved lines, the prevailing relative humidity will be shown by the location of the index arm over the scale at the bottom of the instrument. Thus the percentage relative humidity may be read directly.

HYGRODEIK

C. THE HAIR HYGROMETER

The hair hygrometer is often spoken of as merely a hygrometer. The principle on which it operates so as to indicate the percentage of relative humidity is different from the principle of the wet and dry bulb thermometer. The hair hygrometer is so called because its operation is based on the fact that human hair with the oil removed, will lengthen with dampness and become shorter when the air is drier.

In constructing a hair hygrometer a bundle of such hair is used. One end is attached to a stationary framework, the other end is fastened to the circumference of a small cylinder and a light spring holds the hair tight. A pointer is attached to the end of the cylinder. As the hair changes length with the variation in the humidity of the atmosphere, it turns the cylinder and moves the pointer over a dial which contains a scale indicating the percentage of relative humidity. This form of hygrometer is naturally easier to read than the wet and dry bulb thermometer arrangement, but is usually not as accurate. In using a hair hygrometer it should be frequently checked up against a wet and dry bulb thermometer and any necessary adjustment can be made by means of a screw which is attached to the instrument for this purpose.

D. RECORDING HYGROMETER

A familiar form of “recording” hygrometer is an instrument consisting of a combination of a wet bulb thermometer and a dry bulb thermometer. This instrument is constructed so that the respective temperatures registered by each of these thermometers will be recorded in the form of lines drawn by pen points on a revolving chart which constitutes the face of the instrument. Thus at all times there will be a continuous record of the wet bulb and dry bulb thermometer readings. From these two readings as recorded on the chart the percentage relative humidity can be readily secured for any given time. In this way the baker will have a permanent record of the existing relative humidity at the location of the “recording” hygrometer.

IX. HEATING SYSTEMS IN THE BAKERY

Heat in the bakery is required for three main purposes:

1. Baking Ovens.
2. Heating of Bake-shop proper.
3. Miscellaneous heating requirements such as for hot water, steam for proof box and ovens, etc.

The construction and heating of bakery ovens is a subject to which the baker should give considerable thought in order to establish the most efficient baking system possible, conforming to his own particular requirements. The heating of an oven, of course, is maintained by an individual system constructed as a part of the oven itself and is therefore distinct and separate from the general heating plant of the bakery building. It is not within the scope of this book to describe the details of the various systems of oven heating other than to discuss briefly some of the fundamental points relative to the maintenance and control of proper oven temperatures. The manufacturers of the various types of ovens as well as bakery engineers have made a special study of bakery ovens and these readily available sources of information should be used by the baker in connection with his own problems.

The heating plant operated to furnish the necessary heating of the building and to supply the heat required for miscellaneous purposes, can be constructed so as to have two boilers,—one supplying the heat for the building—the other supplying steam for the proof box, oven and for hot water, etc. With such an arrangement only the one boiler supplying steam for the oven and proof box will have to be operated in the hot summer season. In large bakeries having a boiler of large capacity,—a suitable arrangement of the piping system together with the proper installation of reducing valves will permit this one boiler to serve the two-fold purpose of heating the building and supplying the moist steam required for the oven.

X. REFRIGERATION

A. DEFINITION

Refrigeration means the reducing of the prevailing temperature or in other words,—cooling or chilling.

B. SYSTEMS OF REFRIGERATION

Every bakery requires some system of refrigeration.

The principal ways in which refrigeration is secured in the bakery is

by the use of ice, cold water or by the operation of a mechanical system of refrigeration.

1. The Use of Ice

The use of ice is practically limited to the cooling of the cold storage room or ice box and as a means of cooling doughs during mixing. The cooling effect of ice is due to the fact that when ice melts, it absorbs a considerable amount of heat, and furthermore, the ice water resulting from the melting of the ice also absorbs additional heat from its surroundings. Thus it is easy to see how the air in an ice box which is properly insulated is maintained at a low temperature and how the temperature of a dough may be reduced by the use of cracked ice which melts and forms part of the necessary water ingredient in the dough batch.

2. Cold Water

Cold water has a limited use as a means of lowering temperature. It is frequently used as a means of cooling the doughs during mixing. The circulation of naturally cold water secured from Artesian wells or other sources through pipes is often used as a means of lowering the temperature in the dough room.

Cold Water Coil

Such a cold water coil may be made of 2 inch galvanized iron pipes, 25 to 30 feet in length. The number of coils required depends on the size of the room. Usually from 12 to 20 coils are sufficient. An arrangement of this sort is illustrated in the following diagram.

3. Mechanical Systems of Refrigeration

Mechanical systems of refrigeration are becoming increasingly popular inasmuch as they eliminate the handling of ice, and permit the establishment of cooling in various sections of the bakery by the operation of a single refrigeration machine. There are several different systems of mechanical refrigeration. One of the best known at the present time is the system employing ammonia.

The principle on which a familiar type of ammonia system operates is illustrated by the accompanying diagram and may be described as follows:—

A tank of ammonia “A” in the liquid form under very high pressure is connected to an expansion valve “B” which releases this ammonia gradually into cooling coils called “expansion” coils “C.” As the ammonia is thus released from its high pressure, it immediately vaporizes in the form of ammonia gas. However, in so doing it absorbs a tremendous amount of heat or in other words produces a tremendous cooling effect. Naturally the expansion coils become very cold indeed and withdraw heat from the surrounding atmosphere.

MECHANICAL REFRIGERATION
Simple Ammonia Compression System

Thus in exercising this cooling effect, the ammonia gas becomes warmed up. In order that the refrigeration system may be continuous, this ammonia gas is then drawn into a compressor, “D” which is equipped with check valves “E and E” so that the ammonia gas may be withdrawn from the exit of the expansion coil system and then pumped out and compressed under a very high pressure. In doing this, however, the ammonia gas becomes very hot and must be cooled and condensed into a liquid so that it may be re-used. This is accomplished by pumping the gas under high pressure thru condenser coils “F” which are cooled by means of cold water which is allowed to trickle over the outside of the condenser pipes. In this way, the ammonia gas is reduced in temperature and condensed into a liquid. However, this liquefied ammonia is still under high pressure and can again be circulated through the entire system in the manner described above. Thus such a system is continuous and the only new supply of ammonia necessary is to replace that which may be lost from leakage.

However, it is very important that the entire ammonia system be kept very tight to avoid any escape of ammonia fumes. Modern refrigeration systems are constructed with this idea in mind.

In some cases the expansion coils containing the cold ammonia gas are used directly as a means of securing the desired cooling effect. In other instances however, brine is used as a means of transporting the refrigeration to any location where it may be required.

When circulating brine is employed, the expansion coils containing the cold ammonia gas are submerged in a brine solution “G” which can be brought to a very low temperature without freezing. Then the cold brine is pumped through cooling coils or pipes “H” located in the cold storage room, dough room, water tank and in some cases the cold brine is circulated through a jacket surrounding the mixer. In this way, the required refrigeration effect can be secured in any location desired.

In laying out a refrigerating system of this nature care is taken to insulate the pipes carrying the chilled brine or ammonia to the place where the actual refrigerating effect is desired so that the cooling effect may not be lost en-route.

There are other types of refrigerating systems than the one described above and also other substances are sometimes used instead of ammonia.

It is advisable to arrange a mechanical refrigerating system so as to have two units cross connected. One of these units can be used to meet the ordinary requirements of the baker and the other used to meet any extra refrigeration necessary or to take the place of the first unit in case of a break-down.

XI. HUMIDIFYING SYSTEMS

Humidity in the dough room and other sections of the bakery is secured by the production of water vapor and its absorption by the atmosphere of the room. Devices which are designed to accomplish this are called humidifiers.

A. A SIMPLE HUMIDIFIER

Perhaps the simplest arrangement for raising the humidity of a room is to heat a pan or tank of water and then to blow the moisture evaporated at the surface of the water out into the room by means of fans. Such an oufit however, is very crude and will not produce uniform results.

B. AN INEXPENSIVE MOISTURE GENERATOR

A simple form of humidifier may be constructed and installed in accordance with the following diagram:

This generator is made of a piece of standard iron pipe 8 feet in length and 8 inches in diameter. The top of this pipe is perforated and small sockets inserted with perforations through the center to allow the moisture to escape. The pipe is equipped with a water inlet and a water oiitlet, and the pipe is to be maintained two-thirds full of water.

Half way below the water level is a brass pipe for steam, equipped at each end with a valve for steam inlet and steam outlet.

By turning steam on, and only slightly opening the steam outlet valve, the temperature of the water will be sufficiently raised to give off the necessary moisture. This is controlled through the manipulation of the steam valves.

The proper amount of water is easily maintained by occasional observation of the water gauge.

Special air conditioning machines though expensive, are preferable. The moisture generator as shown in the above diagram is to serve those who find the installation of special machines beyond their means.

A surprisingly small amount of steam is necessary to maintain the required humidity.

C. ATOMIZING SYSTEM OF HUMIDIFYING

A familiar type of mechanical humidifier consists of a device having a vertical disk which is revolved at high speed. A stream of heated water is directed against the center of the disk. In this way the water is atomized or broken up into a very fine mist.

A fan rotating back of this disk blows the tiny particles of water out into the room and they are absorbed by the air,—thus raising the humidity in the room.

Such a humidifier is often equipped with a regulator which controls the amount of moisture diffused into the room and shuts it off entirely when the desired humidity of the room is reached.

D. STEAM AS A SOURCE OF HUMIDITY

Low pressure steam, 5 to 15 lbs. gauge pressure, frequently termed “wet” steam is used as a means of securing the desired humidity in ovens. In those cases where there is no automatic humidifying equipment low pressure steam is often used as a means of securing the proper humidity for the proof box.

XII. AUTOMATIC CONTROL OF TEMPERATURE AND HUMIDITY

A. REGULATORS GOVERNING HEAT AND HUMIDITY SUPPLY

Temperature and humidity in the bakery may be controlled by the installation of regulating devices which control the amount of heat and moisture supplied. Thus a fairly even temperature and percentage of relative humidity may be maintained.

B. AUTOMATIC AIR CONDITIONING EQUIPMENT

There are several different types of air conditioning equipment which have been perfected to meet the requirements of the bakery. Such equipment is constructed so as to wash air, incorporate into it the desired moisture content and also bring it to the desired temperature. This washed, humidified and heated air is forced to circulate through the room and the atmospheric conditions therein are thereby standardized and regulated.

A familiar type of such an air conditioning equipment draws in air by suction. This air is forced through a spray or mist of water which washes it and also saturates it with moisture. By careful regulation of the temperature of this water the amount which is absorbed by the air is controlled. This humidified air is then passed through a radiator consisting of heated steam coils and is thus heated to any degree of temperature desired.

Air conditioning equipment may be constructed so that the air may be cooled instead of heated whenever necessary.

The air thus conditioned is circulated through the dough room or any other room where automatic control of the temperature and humidity is maintained, and then often returned to the air conditioning equipment for re-conditioning and re-circulation.

The use of such equipment enables the baker to manufacture his own -weather in the bakery no matter what the natural weather conditions on the outside may happen to be.

XIII. STORAGE CONDITIONS—TEMPERATURE AND HUMIDITY

A. FLOUR ROOM

Flour should be stored in a clean, light, well ventilated room. The average temperature of the flour storage room should be maintained at about 70 degrees F. The relative humidity should be about normal or 65%. In the winter time the material in storage should not be kept too close to the radiator and the heat should be uniformly circulated throughout the room. A suitable thermometer and hygrometer should be placed in some central location in the flour room so that the baker can know at all times the temperature and humidity, and in this way maintain the desired conditions.

Salt, sugar and other dry materials of a similar nature may be kept under the same storage conditions as flours.

B. REFRIGERATED STORAGE

Yeast, and other similar perishable ingredients should be kept in a cool chamber maintained at a temperature of 40 to 45 degrees F. When possible, eggs are often stored at a still lower temperature. It is important

that condensed milk, malt extract, shortening and wax paper be stored under cool, dry conditions.

If ice is employed as the refrigerating agent, of course, the range of refrigerating temperatures which can be obtained is naturally more limited than if some system of mechanical refrigeration is used.

XIV. DOUGH ROOM—TEMPERATURE AND HUMIDITY

A. IMPORTANCE OF TEMPERATURE AND HUMIDITY IN THE DOUGH ROOM

In Chapter XI the very important effect of temperature and humidity on the fermentation and conditioning of the dough was described. In this connection, the maintenance of the proper atmospheric conditions in the dough room is absolutely necessary in order to insure the efficient production of uniform high quality bread.

B. THE PROPER TEMPERATURE AND HUMIDITY FOR THE DOUGH ROOM TO BE MAINTAINED

Under ordinary conditions, the dough room should be kept at a temperature of 78 degrees to 80 degrees F. and a relative humidity of about 70 to 75%. The relative humidity should never go below 65% which represents normal air condition. Without any artificial source of humidity, the humidity in the bakery is usually lower than out-doors inasmuch as the ovens are continually drying out the air. It is often found, especially in cold weather that the moisture content in the air of a bake-shop is lower than it should be, thus impairing the quality of the resulting bread.

The correct relative humidity for the fermenting room may be calculated by adding the actual moisture content of the flour to be used to the percentage of liquid added to the dough batch. Example:

C. IMPORTANT POINTS IN THE MAINTENANCE OF PROPER TEMPERATURE AND HUMIDITY IN THE DOUGH ROOM

1. Construction of Dough Room

While the dough room should be. of ample size, it should not be unnecessarily large and the ceilings should be fairly low, usually not more than nine or ten feet in height, inasmuch as the cost of maintaining the proper temperature and humidity depends on the cubical space of the room.

The dough room should be carefully constructed and if possible the walls and ceilings should be made of material which will act as a heat insulator. Furthermore, if the ovens are located below the dough room the heat radiating from them is apt to “pocket” under the ceiling thus localizing some heat thru certain sections of the floor of the dough room. In order to prevent, this, the space underneath the floor should also be adequately insulated. Cork board and similar insulating material are used to good advantage in the construction of dough rooms, and result in easier and cheaper control of the temperature and humidity of the dough room.

The dough room should be provided with ample facilities for ventilation which can be readily controlled and so arranged that the circulation of air will be uniform and all drafts eliminated.

2. Heating and Humidification Facilities for the Dough Room

(a) HEATING AND COOLING

The necessary heating of the dough room may be secured by the proper installation of radiators which should be so arranged that the neat secured therefrom will be uniformly distributed throughout the room. Cooling of the dough room may be secured by means of the cold water coil which was explained earlier in this chapter or by the installation of a system of refrigeration coils through which is circulated chilled brine secured from the mechanical refrigeration plant. Sometimes the expansion coils containing the cold ammonia gas produced in the refrigerating plant is used. In either case these cooling coils are located near the ceiling of the dough room. The air located near these coils becomes chilled and inasmuch as cold air is heavier than warm air, it will sink to the floor of the room and in so doing a circulation of cooled air is secured throughout the room.

The temperature of the dough room should be constantly recorded by means of a suitable thermometer and where possible, controlled and kept uniform by the operation of the thermostatic regulating devices.

(b) HUMIDIFYING

In addition to the operation of some sort of a mechanical humidifier such as was previously described in this chapter, the creation of the desired humidity in the immediate location of the troughs containing dough may be facilitated by placing the troughs fairly close to each other and also by covering the troughs with canvas cloths.

(c) AUTOMATIC AIR CONDITIONING

In bakeries where circumstances permit the installation of automatic air conditioning equipment such as previously described, the desired temperature and humidity may be readily maintained in the dough room and uniform atmospheric conditions thus insured. In any event, however, the use of a thermometer and hygrometer in the dough room is indispensable.

XV. CONTROL OF TEMPERATURE OF DOUGH OUT OF MIXER

A. IMPORTANCE

As pointed out previously, the maintenance of proper dough fermentation and conditioning depends largely on the temperature of the dough fr6m the time it is mixed until baked. The influence of the temperature and humidity of the atmosphere in the dough room has also been explained. The temperature of the dough when it is mixed is naturally of primary importance and should be carefully controlled.

B. MEANS OF COOLING DOUGHS DURING MIXING

If necessary precautions are not taken, a dough would ordinarily come out of the mixer at a temperature too high to permit optimum fermentation and conditioning. Hence, adequate provisions must be made in order to keep the temperature of the dough down to the desired point. This may be done in several ways:

1. Chilled Air

One very effective way of keeping the dough cool during mixing is by the injection of refrigerated air into the mixer. This is sometimes done by forcing chilled air through small holes in the agitator arms.

2. Cooling Jacket or Mixer

In order to secure the desired cooling effect on the dough during mixing, some mixing machines are constructed with an outer jacket through which cool water or brine may be circulated.

3. Cold Water and Ice as a Dough Ingredient

One of the best known methods of preventing doughs from heating up in the mixer is by the use of cold water and ice as an ingredient in, the dough batch to meet the necessary water requirements. One way in which very cold water is secured is by the installation of brine coils in the tank containing the water to be used in the dough. Such a tank of course, should be carefully insulated.

XVI. CALCULATION OF WATER TEMPERATURE AND AMOUNT OF ICE

A. IMPORTANCE OF UNDERSTANDING METHOD OF CALCULATION

When either chilled air or a cooling jacket is employed, the baker can determine by experience just the amount of cooling required to bring his doughs out of the mixer at the required temperature. With the use of cold water and crushed ice as a means of cooling the dough, the temperature of the water required and the amount of ice needed will have to be calculated.

Therefore, it is highly important that the baker thoroughly understand the mode of calculation involved as explained in the following paragraphs.

B. NECESSARY FACTORS PRELIMINARY TO CALCULATION

In order to calculate the required temperature of the water to be used in any dough and the amount of ice needed, the following factors must be established:—

1. Desired Temperature of Dough Out of Mixer

This, of course, is known by the baker.

2. Temperature of the Flour

This can be secured by use of a Thermometer.

3. Temperature of Dough Room

A thermometer placed in the room near the mixers should be read just prior to mixing so that the room temperature will be known.

4. Machine Allowance

In the following paragraphs the term “machine allowance” is used to designate the number of degrees by which the temperature of the water used in the dough will have to be reduced in any given case to compensate for the normal increase in temperature of dough due solely to the heat developed in the dough by the friction of the mixer and dough.

This machine allowance in some instances may be as high as 35 degrees F.

Inasmuch as the exact machine allowance depends upon the size and type of mixer, the size of dough, stiffness of dough, speed of mixer, type of agitator, and time of mixing, this factor must be determined in each case by the following procedure:

Mix your regular dough noting the temperature of the flour, the temperature of the water, and the temperature of the dough mixing room and also record the temperature of the resulting dough out of the mixer. Then for this particular type and size of dough, mixing time and mixer, the machine allowance to be used must be calculated as follows:—

1. Multiply the dough temperature secured by three.
2. Subtract from this the sum of the temperatures of the flour, water and dough mixing room.
3. The result secured will be the machine allowance.

Example: —

Suppose the dough temperature secured is............80 degrees F.

Then............................80 times 3 will equal 240 and suppose:

Therefore, Machine Allowance in this particular case will be 240 minus 212 or 28 degrees F.

Note:—In order to make this matter clearer, let us suppose,—for instance that it were possible to mix a dough with no heat of friction developed during the mixing process. In such a theoretical case, the temperature of the dough out of the mixer would be practically equivalent to the sum of the temperatures of the flour, water and room divided by 3. Thus, assuming no heat of friction is developed, the above dough directly after mixing would have a temperature of 70%° F. calculated as follows:

If as shown above, however, actual practical experimentation shows that the dough really comes out of the mixer at a temperature of 80° F., then the heat of friction during the mixing process obviously has brought about an increase in the temperature of the dough of 9%° F. This can only be offset by adequate refrigeration or by reducing the temperature of the water used by 28° F. This represents the machine allowance as above calculated.

C. METHOD OF CALCULATING WATER TEMPERATURE REQUIRED TO GIVE DOUGH TEMPERATURE DESIRED

As soon as the temperature of the flour and room have been recorded and the machine allowance determined as shown above,—the necessary procedure in calculating the water temperature required is as follows:

Multiply the desired dough temperature by 3. Subtract from this the sum of the temperature of the dough room, the temperature of the flour and machine allowance. The result will be the temperature of the water required.

Example:—

Suppose also in this case —

Therefore temperature of water required is 231 minus 177 degrees or 54 degrees F.

D. METHOD OF CALCULATING AMOUNT OF ICE NEEDED TO REDUCE TAP WATER TO ANY DESIRED TEMPERATURE

Now after the required temperature of the water is determined as shown above, the amount of ice to be used can be calculated as follows:—

First record the temperature of the available tap water. Subtract the temperature of the water required from the temperature of the tap water. Multiply this difference by the total weight of water for the dough batch and divide this result by 144.

The resulting figure gives the amount of ice required. Deduct this amount from the total pounds of water required to give the amount of tap water needed.

For instance, suppose 240 pounds of water at 54 degrees F. are required, and the temperature of the available tap water is 64 degrees—how much ice should be used?

This is determined as follows:

64 less 54 equals 10

10 times 240 equals 2400

2400 divided by 144 equals 16 2/3

Therefore, 16 ²⁄₃ lbs. of ice is required and 240 minus 16 ²⁄₃ or 223 ¹⁄₃ lbs. of tap water is to be used with the ice.

Note:

This method gives about 20% more ice than would result from strictly theoretical calculation. However, the above has been positively determined on the basis of many practical observations,—taking into consideration the difference due to unavoidable radiation, and applies to one barrel or larger doughs employing a high speed mixer.

For small batches made in slow speed mixers about 10% less ice can be used. This difference depends on shop conditions and can be determined locally.

XVII. MAKE-UP ROOM—TEMPERATURE AND HUMIDITY

The temperature of the make-up room usually is not given sufficient thought and consideration probably due to the shortness of the time required for the dough to be divided and made up. While excessively high temperatures in the make-up room should be avoided, the room temperature should not be any lower than that of the dough room;—about 82 to 84 degrees F. ordinarily will be satisfactory. In many shops, however, the temperature is much higher, due to the nearness of the make-up machines to the baking ovens which naturally radiate some heat. During the handling of the doughs and especially in the “short” proof process, the dough should be protected from all drafts.

In cases where make-up machinery is employed the relative humidity of the room should be about 60 %. In many instances the relative humidity of the make-up room is low, due to the escape of some heat from the ovens. A thermometer and hygrometer should always be located in the make-up room.

XVIII. PAN PROOF BOX

A. IMPORTANCE OF PROPER TEMPERATURE AND HUMIDITY IN THE PROOF BOX

The lack of proper temperature and humidity conditions in the proofing cabinet is one of the chief causes of inferior bread. The importance of the maintenance and control of these two factors therefore, can not be over emphasized. As explained previously, the proper temperature of the proof box for ordinary types of dough should be from 90 to 95 degrees F., and a relative humidity should be from 80 to 85%. Special doughs may require slightly different proofing conditions. The use of a thermometer and hygrometer together with adequate means of controlling the temperature and humidity is indispensable.

The effect of temperature and humidity of the proof box on the dough and finished loaf is discussed in Chapter XI.

It is a very serious mistake to make a dough with insufficient yeast which requires a long fermentation period and then to “force” the dough during proofing with the hope of securing the desired results, inasmuch as it is impossible to produce good quality bread in this manner.

While humidity in the proof box should be sufficiently high to prevent the dough loaves from crusting, it is an error to maintain a humidity so high that drops of water condense out on the ceiling of the proof box, inasmuch as these drops of water may fall on the loaves making unsightly spots and resulting in “cripples.”

An over-heated and over moist proof box injures the texture and grain of the finished loaf.

B. MEANS OF MAINTAINING PROPER TEMPERATURE IN THE PROOF BOX

1. Construction and Location of Proofing Cabinet

The proofing cabinet should be constructed so that the temperature may be maintained uniform throughout. It is advisable to see that the temperature outside of the proof box is fairly uniform on all sides. If for instance, one wall of the proof box is next to the oven and another wall is adjacent to the outer wall of the building,—the side nearest the oven very likely will be much warmer than the side next the wall of the building and under such conditions it would be difficult to maintain a uniform temperature throughout the proof-box. The proof box should be carefully and uniformly insulated.

2. Heat Supplied by Closed Steam Coils

The necessary heat in the proof box is frequently secured by the installation of closed coils or pipes carrying steam. These pipes should be so arranged at the bottom and sides of the proofing cabinet that a uniform circulation of heat can be secured. It is practically impossible to control the temperature with such an arrangement unless some sort of temperature regulating device is installed which automatically controls the opera-

tion of the steam valves so that the desired temperature may be obtained and kept constant.

3. Electrically Heated Proof Boxes

In some shops, especially small ones, the proof boxes are heated by means of electric heating units which are thermostatically controlled in order to insure constant uniform temperature.

4. Automatic Air Conditioning for Proofer

One of the most satisfactory ways in which to secure the desired temperature and humidity in the proof-box is by the installation of a special automatic air conditioning equipment. Special types of such equipment have been designed for such purposes. In this way, air of a definite temperature and humidity is continually entered into the proof box at the bottom, circulated throughout and returned thru the top of the proofer—for re-conditioning and re-circulation.

C. MEANS OF MAINTAINING THE PROPER HUMIDITY IN THE PROOF BOX

1. Heating Pan of Water

Some bakers who lack facilities for the proper conditioning of the air in the proof box have merely placed pans of water at the bottom of the proofing cabinet and slowly heated the same by means of a gas burner or otherwise.

Such a system of course, will create some humidity in the proofer—but it is bound to be more or less irregular in amount and practically impossible to control with any accuracy. Sometimes a better distribution of moisture is secured by the use of wicking arranged so that the wet surface exposed may be thereby increased.

2. Injection of Low Pressure Steam

Low pressure “wet” steam is very often employed in order to produce the desired humidity in the proof box. In some instances a pipe or series of pipes is installed at the bottom of the proofing cabinet carrying steam at low pressure, which is allowed to escape through small holes thus introducing the necessary water vapor into the air. In such cases, adequate facilities should be made for draining off any condensed water from the bottom of the proof-box.

Another system of introducing the low pressure steam is through pipes which are enclosed in pipes of larger diameter. The inside pipe is perforated on the lower side and the other pipe has perforations on the top side. Thus the steam passes up through these holes in the outer pipe. Such an arrangement of low pressure steam pipes may be installed at the bottom and ends of the proof box and also at intervals between the racks in order to distribute the moisture more uniformly throughout the entire chambers.

A similar method of injecting low pressure steam into the proofing cabinet is to arrange the low pressure steam pipes outside of the proof box, with jets spaced at definite intervals leading into the proof box. In case the proof box contains two or more racks, similar steam pipes are installed between the racks for the introduction of low pressure steam at these points. By regulating the valve controlling this system the desired humidity can be created and distributed uniformly.

It is, of course, a mistake to attempt to secure the desired temperature of the proof box by means of the introduction of steam. If this were done, the resulting humidity would be excessive, and damaging to the dough loaves. Therefore, the heating and humidifying systems for the proofer should be separate and independent.

3. Automatic Air Conditioning

The purpose, construction and operation of such equipment has been previously described. It is one of the easiest and best means of securing proper humidity at all times in the proofing cabinet and insures satisfactory control which is difficult to secure by the use of other systems which require frequent regulation and adjustment of valves.

XIX. OVEN BAKING TEMPERATURE AND HUMIDITY

A. HEATING OF OVENS

The baking process has been briefly discussed in Chapter X; and the effect of oven temperature and humidity on the bread has been taken up in Chapter XI.

There are of course, different types of ovens and different kinds of fuel which may be used. While it is not within the scope of this book to discuss oven construction and operation it may be well to point out that the installation of a modern oven designed to meet the particular requirements of the individual bakery is very essential to the efficient operation of the bakery in question. The heat of an oven is generated by the combustion or burning of fuel in the firing chamber. It is well to remember that there is always a “lag” period between the time of firing and the actual heating of the baking chamber and in like manner there is a similar “lag” period in the cooling of the oven. In other words, some time is required for the oven to heat up and to cool off. The duration of this “lag” period is of course, dependent on the type of oven, and kind of fuel used. This period will vary in different shops and must be determined locally in each individual oven.

For satisfactory results, the heat of the oven should be maintained solid and steady. This is important from the standpoint of fuel economy as well as quality in the finished baked goods.

In the general use of an average peel oven, it is a fallacy to build a quick or heavy fire, but in those cases where the capacity of the oven must be forced to the limit it is frequently necessary to maintain a “sharp” fire. It is well to build a sharp fire about three hours previous to baking and close the dampers about % way about two hours after the fire has been started. Then add a moderate amount of fuel each hour thereafter in order to keep a continuous live fire under the oven during the baking hours. The fire should be checked about two hours before baking is completed. Care should be taken to see that all flues are kept clean and that the chimney is high enough to produce the desired draft. The use of the proper fuel and care in the method of firing the oven will result in fuel economy and aid in the proper control of oven temperatures at all times.

B. OVEN TEMPERATURE AND ITS CONTROL

As pointed out in Chapter X, oven temperatures for ordinary bread making are usually maintained within a range of 375 degrees to 450 degrees F.,—the exact temperature required being dependent on the type of bread and size of loaf. Ordinarily the temperature of the oven should be such that the loaves will start to “color” in about twelve minutes after being placed in the oven.

Most baking ovens are so constructed that the top and bottom heat may be controlled within certain limits so as to conform to the type of loaf being baked. The oven temperature secured naturally depends on manner of firing and operation of the dampers. Many modern ovens are equipped with thermostatic regulators which control the temperature of the oven automatically either by adjusting the fuel supplied or by properly operating the dampers.

Flash heat, or temporary excessive oven temperature at the start of the baking process should be avoided, inasmuch as it will cause a rapid crust formation which will color too deeply and sometimes burn before the inside of the loaf is properly baked.

Flash heat in an oven may be removed by opening the damper to the baking chamber as well as the oven door and allowing steam and air to pass through for about five minutes prior to baking.

If, on the other hand, the oven temperature is too low, much longer time is required for baking, and the dough will therefore lose more moisture and the finished loaf will become stale much sooner than if the proper baking temperature were adhered to.

Instruments for measuring and recording oven temperatures have been described previously in this chapter.

Thermometers or thermocouples of course, register the temperature at the spot where they are located. Therefore, it is wise to have several such instruments distributed at various points in the oven so that the baker may be enabled thereby to properly regulate the temperature throughout the entire oven.

C. HUMIDITY IN THE OVEN

1. Purpose of Moist Steam in the Oven

The desired humidity in the oven is secured by the injection of low pressure moist steam which “mellows” the heat and produces the following results:—

(a) FACILITATES OVEN SPRING

The proper amount of low pressure steam in the oven prevents the crust from forming too rapidly, thus insuring a healthy uniform oven spring and a loaf of good symmetry and volume. Such a condition also assists in the production of good grain and texture within the loaf.

(b) ASSISTS IN THE DEVELOPMENT OF GOOD CRUST AND BLOOM

The presence of moisture in the oven assists in promoting the chemical changes in the starch and sugar at the exposed surface of the dough which are responsible for the development of a soft thin crust having a desirable golden color. Steam also prevents the formation of cracks in the crust and imparts a gloss or glaze to the crust which is desired in some types of bread.

2. Low Pressure Steam as a Source of Oven Humidity

While the normal evaporation of moisture from the dough during baking assists to a limited extent in the production of humidity in the oven, it is necessary in most cases to introduce low pressure steam into the oven in order to maintain the desired amount of moisture. The steam used for this purpose should show a gauge pressure at the oven of from 5 to 15 pounds and when actually entered into the oven it is often spoken of as “wet” steam, due to its partial condensation and the resulting formation of tiny particles of moisture which make the steam visibly moist or wet.

It is essential that a pressure gauge be installed in the steam line at the entrance of steam into the oven and that the readings on this gauge be used to indicate the pressure and temperature at which the steam enters the oven. Frequently due to the length and arrangement of the piping system from the boiler, steam which shows a fairly high pressure at the boiler will be greatly reduced in pressure and temperature by the time it actually reaches the oven.

If a high pressure boiler is in use, a check valve should be placed on the outlet of the boiler leading to the ovens, but if the distance is great, the check valve should be installed at the point where steam lines divide the supply of steam to the ovens.

In this way a continuous supply of low pressure steam can be readily maintained.

All steam pipes should be covered with insulation material. Especially is this important for those leading to the oven.

Frequently, such insulation covering pays for itself in one year through saving in fuel, besides providing a more normal supply of steam to the ovens, with less free water, which by spraying into the oven, often spoils the bread.

All steam fixtures require a drain where steam enters oven to drain accumulation of water settling in the pipes.

3. Amount of Steam to Use in Oven

The amount of moist steam to be injected into the oven depends on the type of bread being baked as well as the tightness of the oven.

For plain pan-loaves, turn valve half way open while oven is being loaded; closing door and turning off steam as soon as this is accomplished.

This is sufficient steam to moisten the heat, making possible a good development of loaf, while the crust of the finished loaf will usually have a dull finish.

If a glossy-finished loaf be desired, continue steam 3 to 5 minutes after oven is filled and the door closed.

Of course, the oven must be steam tight; if there is a leak in crown or flues of ovens, steam must be allowed to enter, until Bread has fully risen in the pans and begins to color. This will require from 8 to 15 minutes according to heat of ovens.

For Vienna Bread, Bottom Rolls, Rye and French Bread, the steam must be allowed to enter oven until Bread is set and begins to take on color.

Split top bread which has been given a shorter proof than plain top bread, also requires additional amount of steam in order to insure a good even “break and shred” and proper gloss. Ordinarily after the steam has been shut off in the oven, the normal evaporation of moisture from the dough will provide adequate humidity. If an excessive amount of steam is used—the crust will be tough, and often crust blisters also will be produced.

4. Explanation of Steam

The use of steam as a source of humidity in the oven as well as the proof box is such an important factor in the production of quality bread that it is very essential for the baker to understand the nature of steam and the kind which should be used for this purpose and also the kind which should be avoided. While it may be generally known that low pressure or “wet” steam should be employed for such work,—just what is meant by this type of steam may not be so well understood. There are three classes of steam, “saturated,” “wet” and “superheated.” These are described in the following paragraphs:—

(a) SATURATED STEAM

If water is boiled in an open vessel or closed boiler, it is vaporized and passes off as steam. Such steam is said to be saturated. If water is heated in a closed boiler the saturated steam thus generated will gradually develop an increasing pressure as the heating is continued. At the same time, the temperature of this saturated steam as well as that of the water in its presence will increase accordingly. Thus the pressure of saturated steam is an indication of its temperature. The greater the pressure of the saturated steam, the higher will be its temperature. This fact is clearly shown by the following table.

SATURATED STEAM
Steam Pressures and Temperatures

(b) WET STEAM

Wet steam is steam which contains within itself tiny droplets of water in the form of a sort of mist or fog. Therefore steam in this condition is said to be “wet” because it actually is “wet.” In the oven the presence of wet steam results in the formation of a very thin film of moisture on the exposed surface of the dough, thus creating the desired effect during baking.

(c) SUPERHEATED STEAM

If ordinary saturated steam is passed through heated pipes, it will absorb some of this heat and becomes very hot. Hence, steam in this condition is said to be “superheated.” Such steam is dry and is not only useless as a source of humidity, but if introduced into the oven or proof box it would have a very injurious effect on the dough and loaf.

XX. COOLING AND WRAPPING OF BREAD

The cooling and wrapping of bread has been discussed in Chapter X. The loaves should be cooled gradually although not too slowly. If they are chilled or submitted to cold drafts directly after being delivered from the oven, cracks in the crust may develop. The relative humidity of the cooling room should be above normal and the cooling period usually will take ly^ to 2 hours. Before being wrapped the temperature of the interior of the loaves should be below 95 degrees F. Under the prevailing conditions in any bakery the exact time required for cooling the bread should be determined locally. If the bread is first allowed to cool on racks for 15 to 20 minutes in the oven room where the temperature is about 85 degrees F. and then removed to the cooling room where a temperature of about 65 degrees F. is maintained, ordinary loaves will be sufficiently cooled in about 1% hours.