Bread making is not just a culinary gift but also science at the same time. There are certain unique requirements of bread making to tickle the taste buds of food connoisseurs. The basic ingredients used in the process are flour, fats, eggs, salt, yeast and water. However, the temperature is an important factor that plays a crucial role as far as making enjoyable bread is concerned. Experts point out that temperature essentially impacts time management, product consistency, crust and flavors and shelf life of bread. The dough temperature is kept at 27 degree Celsius, flour temperature at 15 degree Celsius. Water temperature is calculated as: 2* dough temperature - flour temperature and it comes out as 39 degree Celsius (Kim and Cornillon, 2001). The dough temperature is largely influenced by ambient temperature, flour temperature, water temperature and temperature emanating from the action of kneading or mixing also called as friction factor (Farahnaky and Hill, 2007 ). Friction, in turn, varies based on manual and mechanical actions as well as how much time does it take. It is generally estimated that the rise of temperature should be 1 degree C per minute for kneading and 2 degree Celsius for mechanical mixing. The temperature of the water is used to control and regulate the temperature of the dough, and it is obtained by using a little bit of calculation.
Temperature of water = (Dough temperature * 3) – (room temperature + flour temperature + friction) = 21 degree Celsius.
With preferment, Temperature of water = (Dough temperature * 4) – (room temperature + flour temperature + friction + preferment temperature) = 25 degree Celsius.
Friction factor = (dough temperature * 3) – (flour temperature + room temperature + water temperature) = 12
With preferment, Friction factor = (dough temperature * 4) – (flour temperature + room temperature + water temperature + preferment temperature) = 14
When preferment is included the water temperature thus obtained is 25 degrees Celsius. However, commercial bakers take into account the required water temperature. They try to keep a stable temperature and use ice (chilled water preferably) to keep the temperature in check as the dough prepared with too hot or too cold water might yield undesirable results and affect the fermentation process (Toyosaki, 2007). A baker’s control on the temperature dependence starts from the very beginning of the dough making process, and its importance cannot be neglected.
The role of yeast in bread making is also very important. It metabolizes free sugars (released by enzymes from starch) for producing carbohydrates and carbon dioxide as well as alcohol as a by-product. C6H12O6 → 2C2H5OH + 2 CO2 . So, one molecule of glucose yields two molecules of alcohol and two molecules of carbon dioxide.
Temperature during fermentation and proofing
The minor fluctuations in dough temperature can affect the bulk fermentation and proofing a lot. After adding dried yeast, the optimum temperature is kept just over 27 degree Celsius. If the temperature is increased further, the activity of yeast declines correspondingly and the temperatures above 35 degree Celsius make yeast dormant or nearly dead. Whereas, at 34 degree Celsius, the bacterial activity is at its peak, that is why some bakers choose to ferment the bread at 32 degree Celsius. The activity of yeast is exactly halved at 21 degree Celsius, and it takes twice as long to ferment. The correct temperature is extremely critical variable for the growth and replication of yeast (Winata and Lorenz, 1997). In the given graph, the growth rates of Lactobacillus and Milleri (yeast) are compared. The duration 0 to 7 is a doubling time (generation time) of one hour. If the doubling time at 20 degree Celsius is half of that at 30 degree Celsius C, the yeast will grow half as fast at 20 degree Celsius compared to 30 degree Celsius. So, it comes out that the ratio of growth to growth rate at optimum temperature matters a lot (method of producing and baking frozen yeast leavened dough, 1997).
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The excessive cool conditions during fermentation and proofing, the dough does not get enough gassing power and hence dough is rigid, tough and flat. In excessive warm conditions, during mixing, dough attains its high gassing power and as a result, dough lacks elasticity, becomes dry and breaks on stretching.
Pathway of alcohol fermentation by yeast:
Secondary fermentation also known as final proof is the period that follows shaping of dough and precedes the baking process. It is done with a purpose of attaining maximum dough development by allowing the final product to be set. Generally, the proofing the proofing temperature used is 22 to 29 degree Celsius. However, these days programmable proofing equipment also called as “proofers” are used to control temperature, time and humidity. The temperature fluctuations during proofing can cause the dough to become too cool, and the resulting product will be compact with a dense crumb. The following graph shows the activity of yeast at various temperatures.
As water and flour exhibit, different levels of thermal capacity and in the process of bread baking this very fact translates to the effects of water on dough temperature being twice that of flour. The adding and not adding salt to the dough also greatly influences its taste. If the salt is forgotten the bread produced has an unpleasant taste. However, it diminishes the activity of yeast so should be added too much.
Water levels for keeping bread crispy
The water quantity is the key to maintaining the crispiness of bread. Scientific results have shown that water activity that determines the migration of water also has the perceived influence in the crispiness of the bread as the water content of crust was found to be critical for transition point. As we know a product’s crispiness badly suffers when moisture gets into it because hydration caused by water makes an amorphous regions of macromolecules (initially in glassy state) transition into rubber form. By altering the relative humidity trajectory in different conditions, bread crust samples were taken, and the effects of water were identified.
Temperature during baking
The process of baking is responsible for transforming uneatable dough into a light, easily digestible, porous and flavored product. The range of temperature used in the baking process is from 93 to 96 degree Celsius. The processes that determine the baking temperature are the expansion of gas cells and coagulation of gluten as well as gelatinization of starch. In the process of coagulation, the protein macromolecules get aggregated into the lumps of semisolid material. The process of gelatinization is defined as the swelling of starch granules on heating in the presence of water (Ahrne, Anderson, Floberg and Lingnert, 2007). If the oven temperature is kept too low, the dough will expand to its greatest extent before the gluten and starch are to set. As a result, the dough collapses into flat and dense mass. On the other hand, if the oven temperature is kept too hot, the protein and starch in the outer layers set too quickly. As a result, the prematurely formed crust will be prevented from further expansion. If we talk about the types of the dough, a lean dough is generally baked at 220 to 233 degree Celsius and rich dough at 175 to 190 degree Celsius. The later one is baked at lower temperatures because the baking process will be more gradual and the outer surface of the dough doesn’t get brown before the interior sets. According to baker’s need, once the crust and shape of the dough are set and become firmer, the temperature of the oven can be lowered to let crust thicken as the center finishes baking. The small and large pieces of dough are needed to be cooked using different methods. Smaller pieces are required to be baked quickly for the crust to become fully brown without crumb getting dehydrated. While, larger pieces are needed to be baked slowly in order to prevent it from getting overly thick and dark before the center of the crumb is cooked.
With the accumulation of internal heat, a lot of reactions occur in the dough. At the temperature of 49 degree Celsius, yeast activity is decreased and on increasing it further to 57 degree Celsius, yeast cells get destroyed. In this temperature range, the expansion of gas cells takes place and during this period the yeast activity regarding producing carbon dioxide work in concert for swelling the dough. It happens within the first 10 minutes. The processes of coagulation of proteins and gelatinization of starch occur at 60 to 72 degree Celsius where the center of the dough continues to accumulate the internal heat. Just below the temperature of boiling, the gluten, starch and semi-liquid from the dough, solidify into the final product.
The browning of the bread and reactions related to it occur only after the water content of the dough reaches its boiling point and starts drying out of its outer surface. The factors responsible for the browning of the bread are caramelization of sugars, dextrinization of the starch and the Maillard reaction. Caramelization is the process of giving up of water and carbon dioxide from sugar thereby altering its structure and taste. Dextrinization refers to changing of starch into dextrin caused by dry heat resulting in increased flavors and digestibility. While, Maillard reaction occurs as a result of interaction between amino acids and carbohydrates. In high temperatures, Maillard reaction results in desirable aromas and flavors. In lower temperatures, on the other hand, Maillard reaction gives flat, gluey and less aromatic flavors. The browning of the surface of the dough is responsible for the improvement of color and taste of final product because the reactions though limited to hot, dry crust, are diffused inward toward the center of the dough. As a result, light colored and dark colored final products have different tastes with dark colored products being more flavorful. Finally, the cooling racks facilitate the evaporation of the steam generated during baking as well as hardening of the crust.
“Oven spring” is the process of expansion of gasses inside the dough that is caused by a series of reactions. The built up of pressure inside the thousand tiny gas cells makes them bigger thereby increased volume. A significant amount of carbon dioxide produced by the yeast at above 40, turns into a gas and moves into gas cells and overall solubility of gasses is reduced and the alcohol produced gets evaporated by the oven heat. At about temperatures of 74 and above, gluten strands surrounding the cells are transformed into semi-rigid structures, and the natural enzymes start dying at different temperatures during the process of baking. One such enzyme known as alpha-amylase, responsible for breaking starch into sugars, keep working until the dough temperature reaches about 75. After dying of the yeast, the extra sugars produced in this period are utilized to sweeten the breadcrumb as well as giving it the attractive brown color.
Some important factors, parameters, and terminologies used in the process of baking dough are:
Volume: an optimum volume having a proper structure, not too open, is used for the dough.
The symmetry of shape: if the ingredients in correct proportion with correct properties are mixed, a symmetrical shape is obtained. It is also obtained using right fermentation and molding.
Bloom: excellent fermentation denotes the natural bloom. It is also brought about by good use of raw materials and workmanship.
Crust color: correct temperature, fine raw materials and properly fermented dough are responsible for crust color.
Oven break: the dough, if correctly processed will break properly in the first period of baking. In case an oven breaks not required, the dough can be given longer final proof.
Internal color: the internal color depends on the type of flour used and structure of crumb.
Sheen and texture: the light being reflected by a cut surface is indicative of the condition of the crust and is called as sheen.
Elasticity: if the crumb on being pressed returns in its original shape, it is called elasticity.
Moistness: the water content and ingredient like fat and malt determine the moistness of the dough.
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