Temperature Control - Part I

 

This article, written by The Artisan Baker,  first appeared in two issues of Bread Lines (Vol. 10, Issues 1 and 2), the Newsletter of The Bread Bakers Guild of America.    We have presented it here in two parts for your convenience.  For those who either are not aware of The Guild, or have not visited their web site, we  have provided a link to same.  We would like to thank Noel Labat-Commess, of Tom Cat Bakery in New York for his generous editorial guidance.

 

Introduction:
 

Whether making bread at home or in a commercial setting, temperature control plays a crucial role in:

  • Time management

  • Product consistency

  • Crust, crumb, and flavor characteristics

  • Shelf life

Considering the scope of the topic, this article will focus upon temperature control in the dough making process, and a subsequent article will focus upon temperature control during fermentation and baking.

The following discussion of baker's yeast (Saccharomyces cerevisiae) is included as a prelude to the discussion of temperature.

The introduction of baker's yeast promoted a reduction in production time by permitting bakers to transition from the indirect method to the faster direct method. It also advanced the production of smaller size bread, and bread of less weight and greater volume (such as the Italian michette or rosette, which when properly produced are nearly empty in the center). Issues that detracted from the introduction of baker's yeast were a reduction in product shelf life and, when the fermentation was too rapid due to excessive temperature or quantity of yeast, a reduction in product quality.

Baker's yeast was originally introduced because it represented a simplified, faster, and more consistent method of bread making. Briefly, the action of Saccharomyces cerevisiae leads to, among other things, the production of carbon dioxide causing the dough to rise during fermentation, the production of compounds that evaporate during baking giving bread its aroma, and modification of the gluten, also referred to as dough maturation.

Brief Literature Review:

A review of the literature afforded no hard or fast rules relative to the temperature of the dough following mixing. Standard practice suggests final dough temperatures after mixing in the range of 70 to 82 F, depending upon whether a preferment or final dough is being prepared.

E. J. Pyler, In "Baking Science & Technology" , suggests setting sponge dough (also generically referred to as preferments) to ferment at temperatures of 74 to 78 F (23 to 26 C), emphasizing that it is desirable to work with cool sponges and adequate levels of yeast. He further suggests setting straight dough at slightly higher temperatures of 77 to 79 F (25 to 26 C), because straight dough contains all of the dough ingredients, such as salt, which has a retarding effect on yeast activity.

In his book, "The Taste of Bread", Prof. Raymond Calvel points out that average mixing temperatures vary between 24 and 25 (75.2 F and 77 F). He goes on to say that mixing temperatures between 26 and 27 C (78.8 F and 80.6 F) lead to oxidation, dough bleaching, and deterioration of bread taste, whereas lower mixing temperatures of 22 and 23 C (71.6 F to 73.4 F) moderate oxidation and dough bleaching, and improve bread flavor. Consistent with this recommendation, is the following authored by Didier Rosada in Volume 6, Issue 2 of "Breadlines": 'To make the most of the fermentation process, the baker needs to make dough with a small amount of yeast, at a temperature around 76 F [24.4 C] after mixing, and use a mixing technique that will allow the dough to adequately ferment before dividing.'

Alternatively, in "Il Pane, Un'arte, una technologia", Piergiorgio Giorilli and Simona Lauri suggest that the final dough temperature does not always have a specific value, but rather, is determined by the type of dough being prepared. For instance:

Consistency Water Content Example  Temperature
Dry Below 50%  farrarese, mantovano  23 C (73.4 F)
Soft 50 to 55% tartine, ciriole 25 C (77 F)
Slack  60 to 65%  francese, ciabatta 27-28C (80.6-82.4 F)

Obviously, the information presented above is for dough produced in Italy. When one takes North American practices into consideration, the information is modified as follows:

 

Consistency Water Content Example  Temperature
Very Stiff Below 50%  farrarese, mantovano  23 C (73.4 F)
Firm to Moderately Firm 60 to 65% tartine, ciriole 25 C (77 F)
Soft to Soft and Slack 65 to 75%  francese, ciabatta 27-28C (80.6-82.4 F)

In general, the modification is due to differences in wheat varieties, milling procedures, and absorption rates.

"Baking, The Art and Science", by Schunemann and Treu, has a good amount of information relative to the consequences of mixing at too high or low a temperature. Schunemann and Treu indicate that the intensity and duration of the mixing process effects the optimal dough temperature. Since slow-speed mixers are susceptible to faster dough maturation, keeping the dough cool leads to the best results. High-speed mixers lead to dough that ages more slowly. In this case, the higher friction (discussed below) compensates for any temperature adjustment. Since yeast activity is greatly reduced at lower temperatures, dough prepared under cool conditions tends to ferment more slowly.

Dough Properties:

 

Excessively Cool Conditions  Excessively Warm Conditions

Matures slowly, and remains "green" or "young" for a long time.

Matures quickly, and gets "old" very fast.

Is moist.

Is dry and tends to form a skin.

Is sticky and runny.

Firms up very quickly.

Is not firm, but rather, "flows".

Turns "short" (less elastic) very rapidly.

 

Loses fermentation stability

Base Temperature Calculation:

How is the temperature of the dough controlled? By using the base temperature calculation. The factors that influence dough temperature are the ambient temperature, the temperature of the flour, the temperature of the water, and the temperature resulting from the action of kneading (manual) or mixing (mechanical). The temperature of each of the first three factors is easily measured by using a thermometer.

The fourth factor, the temperature resulting from the action of kneading or mixing, is known as the friction factor. The friction factor refers to the amount of energy or heat generated during the dough making process. Friction varies according to whether the action is manual or mechanical, how much time the action takes, and the firmness of the dough. If the action is mechanical, friction also depends upon the type of mixer used. There is disagreement regarding estimates of how many degrees the dough temperature may rise during kneading and mechanical mixing. Some suggest 1 degree per minute for either method. Others suggest 1 degree per minute for kneading, and 2 degrees per minute for mechanical mixing, no matter which type of mixer is used. These differences emphasize the importance of calculating the friction factor independently.

Here is how to calculate the friction factor: Prior to making the dough, note the exact temperature of the room, flour, and water. After the dough is made, note the dough's temperature. We are working with three factors that effect dough temperature; the temperatures of the room, flour, and water. Consequently, it is necessary to multiply the temperature of the dough by three. After doing this, add the three temperatures; room, flour, and water and subtract the sum from the temperature of the dough multiplied by three. The result is the energy or heat of the friction generated either manually or mechanically. This is illustrated in the Table below:

 

 
Dough Temperature = 74 F
Multiplied by 3  

=  

222 F
   
Room Temperature =   68 F
Flour Temperature =   72 F
Water Temperature =   70 F

Sub-Total = 

210 F
   
Subtract Total from  222 F 222 F
- 210 F
 Friction = 12


Of all the factors that influence dough temperature, i.e. room, flour, water, and friction, the temperature of the water is the controlling factor in regulating the temperature of the dough. Once the friction factor has been established, the necessary water temperature can be calculated. Prior to making the dough, note the exact temperature of the room, the flour, and the friction factor. Also, note the desired dough temperature. Since we are working with three factors; the temperature of the room, the flour, and the friction factor, multiply the desired dough temperature by three. Add the three temperatures; room, flour, and friction, and subtract the sum from the desired dough temperature multiplied by three. The result is the required water temperature. This is illustrated in the Table below:

 

 
Dough Temperature Desired 77 F
Multiplied by 3  

=  

231 F
   
Room Temperature =   68 F
Flour Temperature =   72 F
Friction =   12 F

Sub-Total = 

152 F
   
Subtract Total from  231 F 231 F
- 152 F
Water Temp. Required = 79


When a preferment is included in the formula, the temperature of the preferment becomes an additional factor. As such, it is included in the sum of the temperature of the room, the flour, and the friction. (Please note that the consistency of the preferment, i.e. loose, firm, etc., may affect the friction factor. If so, it is necessary to determine the friction factor when using a preferment of a particular consistency.) Since we are now working with four factors, the desired dough temperature must be multiplied by 4. This is illustrated in  the Table below:
 

 
Dough Temperature Desired 77 F
Multiplied by 4  

=  

308 F
   
Room Temperature =   68 F
Flour Temperature =   72 F
Pre-Ferment Temperature =   70 F
Friction = 12 F

Sub-Total = 

222 F
   
Subtract Total from  308 F 231 F
- 222 F
Water Temp. Required = 86


Commercial bakers sometimes use ice to lower the water temperature to the degree required, especially when they do not have water-jacketed or refrigerated mixer bowls, i.e. mixer bowls that circulate chilled water or refrigerants through coils between the walls of the mixing bowl, or CO systems that cool their flour as it moves through pipes toward the mixer. Again, disagreement exists. While using ice is considered a time-honored practice by some, others think it may cause damage to the mixer, inhibit the development of the yeast (thereby inhibiting fermentation), and break down the dough. A good water chiller will cool water to just above freezing and this is the most common solution.

A mix of dough is a large mass and its difficult to effectively change its temperature within a time frame that suits a baker's needs. A dough mixed too hot to too cold will yield undesirable results downstream as fermentation proceeds too quickly or too slowly. A difference plus-or-minus 2C (3.6F) will noticeably affect many of the bread's qualities, either directly or by changing the ratio of lactic to acetic acid, for example, or indirectly, by causing the baker's schedule to change to adjust to the faster or slower fermentation. The baker's control of the dough starts from the moment he or she opens the tap; the importance of controlling the dough's temperature in the mixing bowl can't be overstated.

Temperature Control - Part II

Whether making bread at home or in a commercial setting, temperature control plays a crucial role in:

  • Time management

  • Product consistency

  • Crust, crumb, and flavor characteristics

  • Shelf life

The first part of this two-part article above focused on temperature control in the mixing process. This second part will focus on temperature control and its effects in fermentation and proofing.

Temperature During Fermentation and Proofing

Primary Fermentation (Bulk Fermentation)

Primary fermentation is also referred to as bulk fermentation. Activity of the ferment, be it bakers yeast or levain (sourdough), is one of the primary factors in the process of dough development during primary fermentation. Consequently temperature plays a vital role in determining the time within which dough development or maturation is achieved for a formula with a specific ferment level. It is customary to adjust the ferment quantity, or fermentation time, or both, with changes in dough temperature, whether those changes are introduced intentionally or unintentionally. Practicing bakers, in both commercial and home settings, are familiar with these relationships and make appropriate adjustments with rises and falls in ambient temperature by either adjusting the amount of ferment, fermentation time or both.

There is some debate as to what is the optimal temperature for dough fermentation. "Il Pane," by Guido Boriani and Fabrizio Ostani, indicates that optimum dough temperature during fermentation is within a range of 20C to 25C (68 to 77F). Below 20C (68F), the action of the yeast is slowed down. Above 30C (86F), it is speeded up. In general, if the seasonal temperature is low, a longer fermentation period is recommended. If the seasonal temperature is high, a briefer period is recommended. Prof. Giovanni Quaglia, author of "Scienza e Technologia della Panificazione" indicates that under ideal conditions the final temperature of the dough should be 25C (77F), and that oscillating temperatures between 20 and 24C (68 and 75.2F) represent optimal environmental parameters during fermentation. For the most part, the formulas in "The Taste of Bread," by Prof. Raymond Calvel, specify fermentation temperatures of 24C and 25C (75.2 F and 77 F).

The argument may not be so cut-and-dried. Different fermentation temperatures can yield correspondingly different results and a versatile baker can make this decision part of his or her toolbox. A change in fermentation temperature will change the proportions of lactic and acetic acid in a dough resulting in markedly different flavor and physical characteristics. A higher fermentation temperature 27C+ (80F) - will cause a noticeable jump in lactic acid production. Lactic acid has a round, mellow flavor that fills the back of the mouth, the flavor you get in buttermilk or yogurt. Breads with a higher lactic acid content taste fuller in the mouth, often have a more open crumb and a thinner, crispier crust. A lower temperature - 22C or less (72F) - will not affect the acetic acid development but will drop the amount of lactic acid resulting in a more astringent flavor that is tighter and sharper in the mouth, the flavor you get in vinegar. Breads with a higher acetic acid content often have a tighter crumb and a thicker, less crispy, chewier crust.

The following tables entitled Dough Conditions During Fermentation, and Quality of the Final Product, are offered as a simplified reference to help determine the causes of defects or faults resulting from inadequate temperature conditions during fermentation.

Dough Conditions During Fermentation:

Excessively Cool Conditions Excessively Warm Conditions
   
Dough does not attain sufficient gassing power during fermentation and proofing Dough reaches the peak of its gassing power during mixing or during make-up

Dough is rigid, tough, and flat

 

Dough lacks elasticity, breaks when stretched, and becomes dry

Quality of the Final Product:

Excessively Cool Dough Excessively Warm Dough
   

Volume is reduced

Volume is reduced

Crust is dark and hard

Crust is pale and whitish
Bread has irregular holes or breaks Bread has large cells with thick walls
Crumb dries out quickly. Crumb is dry, crumbly and, at times, sour tasting
Crumb is uneven, dense in the center or open outside Crumb is gray
Aroma and flavor are poor Aroma and flavor are poor
Shelf life is reduced Shelf life is reduced
   

Intermediate Proof (Benching or Bench Time):

Intermediate proof is also referred to as benching or bench time. It is a period of rest between the work carried out by dividing and rounding (an activity during which dough temperature becomes evenly distributed), and final shaping. The purpose of this rest period is to allow the dough to become sufficiently soft, extensible, and relaxed to perform well during shaping, and to further fermentation development. During intermediate proof the activity of the ferment continues to generate carbon dioxide. The extent of the activity depends primarily upon the dough temperature, and the length of time involved. The result of the activity is that the gas bubbles in the dough begin to increase in size. For this reason, this period can be used to influence the structure of the final product. An adequate intermediate proof is thought of as critical in the development of products with an open cell structure. Provided there is limited structural modification, and degassing is minimized during final shaping, a longer intermediate proof time, e.g. 15 minutes or more, will result in a more open cell structure in the final product. The temperature during intermediate proof should be consistent with the temperature during primary fermentation.

Secondary Fermentation (Proofing/Final Proof):

Secondary Fermentation is also referred to as proofing or final proof. It is the period of time that follows shaping and precedes baking. The purpose of proofing is to obtain maximum dough development by allowing the shaped dough to relax and expand to produce an aerated piece of dough which, when baked, produces the desired shape and volume. During proofing, the structure of the final product is set.

Proofing temperatures generally occur within a range of 22C to 29C (72F to 85F), depending upon the formula and final product. Many commercial bakers have access to programmable equipment referred to as "proofers" or "proofing cabinets," which allow for the ultimate control of such factors as temperature, time, and humidity. Those bakers who do not employ specialized equipment, and those of us baking at home, tend to identify areas within our environment in which the temperature is naturally or easily controlled, and devise makeshift techniques to have an affect on humidity.

If the dough is proofed at an improper temperature, or if there are fluctuations in temperature during proofing, the following defects or faults may occur: The dough may become too cool, resulting in a final product that is small and compact, with a dense crumb structure. The dough may form a skin, inhibiting expansion during proofing and baking, and causing a pale, dull, and thick crust,

Temperature During Baking:

Although the definition of "baked" is considered arbitrary by some, a range in temperature from 93C to 96C (200F to 205F), at the center of a lean dough at the end of baking, is the generally accepted standard. This is the temperature necessary for the structure throughout the final product to be adequately rigid. For a rich dough, the standard is 82C to 87C (180F to 190F).

Two processes determine baking temperature. One is the expansion of gas cells, and the other is the coagulation of gluten and gelatinization of starch. Coagulation is described as the aggregation of protein macromolecules into clumps or aggregates of semisolid material. Gelatinization is described as the swelling of starch granules when heated in the presence of water. Too low an oven temperature will cause the dough to expand to its greatest extent before the gluten and starch have had an opportunity to set. The dough will then collapse into a flat, dense mass. Too hot an oven will cause the protein and starch in the outer layers to set too quickly. The crust, prematurely formed, will prevent further expansion.

Lean dough is usually baked at 218C to 232C (425F to 450F), while rich dough is usually baked at 176C to 190C (350F to 375F). Rich dough is baked at lower temperatures than lean dough so that the baking process is more gradual and the surface of the dough doesn't brown before the interior has set. If desired, once the shape of the dough has set and the crust has become firmer, the temperature of the oven can be reduced to allow the crust to thicken as the center finishes baking.

Size matters here as it does in cooking, and opposite strategies are called for to properly bake small and large dough pieces. A small piece must be baked quickly in a hot oven so that the crust can fully form and brown without the crumb becoming dehydrated. A large piece must be baked slowly in a cooler oven so that the crust doesnt become overly thick and dark before the center of the crumb is adequately cooked.

A variety of reactions occur as the dough gathers internal heat. Yeast activity is decreased at 49C (120F), and yeast cells are destroyed within the range of 57C to 60C (135F to 140F). The first process which determines baking temperature (the expansion of gas cells) occurs within this temperature range. During this period, yeast activity in the form of the production of carbon dioxide and the expansion of gas volume as the dough heats up, work in concert to swell the dough and produce oven spring. This generally occurs within the first 7 to 10 minutes of baking. At approximately 60C to 71C (140F to 160F), the second of the aforementioned process' occurs, namely, the coagulation of the protein and the gelatinization of the starch. As the center of the dough continues to gather internal heat to a temperature just below that of boiling, the gluten and starch, and the semiliquid form of dough, solidifies into the final product.

Browning reactions occur only after the water contained in the dough has reached the boiling point and follow the drying out of its surface. Browning is due to the following three factors: the carmelization of the sugars, the dextrinization of the starch, and the Maillard reaction. Carmelization occurs when the sugar gives up water and carbon dioxide, changing the structure of the sugar and its taste. Dry heat causes the change of starch into dextrines (dextrinization) which imparts flavor and increases digestibility. The Maillard reaction is the result of an interaction between amino acids and carbohydrates in which an aromatically perceived substance is formed. When the Maillard reaction takes place at a high temperature, it results in desirable aromas and flavors, but when it takes place at lower temperatures, it results in flat, gluey, and cardboard-like flavors. The browning of the surface of the dough improves both the color and taste of the final product. Even though these reactions are limited to the hot, dry crust, the flavor of the entire final product is affected, because the products of these reactions are diffused inward toward the center of the dough. Distinctions in flavor can be made between light colored and dark colored final products. Dark colored final products are more flavorful. Once the final product is removed from the oven, it is necessary to allow it to cool on racks. This facilitates the evaporation of the steam generated during baking and the ultimate hardening of the crust.

The following table entitled Dough Conditions During Baking, and Quality of the Final Product, are offered as a simplified reference to help determine the causes of defects or faults resulting from inadequate conditions during baking.
 

Dough Conditions During Baking - Quality of the Final Product

Excessive Top or Bottom Heat

 

Excessive Top Heat  Excessive Bottom Heat
   
Separation of the crust from the crumb with irregular swelling on the surface

Wide, flat shape and a hard base

Crust is too dark Crust is pale.

Excessively Cool or Hot Oven

 

Excessively Cool Oven  Excessively Warm Oven
   

Crust is irregular, torn

Separation of the crust from the crumb with irregular swelling on the surface

Crust is pale, dry, thick Crust is dark, red, and hard

Volume is excessive or deficient

Volume is poor
Crumb is gray and dull Crumb is dry
Texture is poor, crumbly Texture is poor, crumbly
Shelf life is reduced Shelf life is reduced
   

Underbaked or Overbaked

 

Underbaked  Overbaked
   

Crust is pale

Crust is dark

Aroma and flavor are poor Aroma and flavor are poor

As these two articles demonstrate temperature control is one of the fundamental issues in the production of quality bread. The baker who manages temperature well manages time well, produces a consistent bread from day to day, and has enormous control over the flavors and textures of his or her breads. Ladies and gentlemen, start your thermometers!

Additional information pertinent to this topic can be found in the following articles: "Starch: II, Starch and Baking," published in Volume 4, Number 2, Spring 1996 of the Guild Newsletter; "The Role of Fermentation in the Baking Process", Breadlines, Volume 6, Issue 2, Spring 1998. "The Retarding Process," published in Breadlines, Volume 7, Issue 4, Fall 1999; and "Choosing an Oven," and "Choosing an Oven - Part 2," published in Volumes 8, Issue 4, November 200, and Volume 9, Issue 1, March 2001, respectively.