Temperature during baking: a crucial factor in bread making

The baking process transforms dough into a light, porous, and flavorful product through the expansion of gas cells, coagulation of gluten, and gelatinization of starch. The temperature range used is from 93 to 96°C. Moisture can negatively impact crispiness by causing hydration and altering macromolecules' glassy state to rubber form. By controlling relative humidity and identifying effects of water, bread crust samples were taken to study the impact of moisture on crispiness.

Effects of water temperature on dough
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).

The activity of the ferment is an important factor for dough development during the process of
primary fermentation. So temperature, again, has to play a crucial role in determining the time of
maturation with a certain ferment level (Fisher, Strasser and Gutzler, 2000). The ferment
quantity and fermentation time are often appropriately adjusted with the rises and fall of ambient
temperature. If at the time of dough making the seasonal temperature is low, then a longer
fermentation period is required and vice-versa. Also, the temperatures oscillating between 20 and
24 degree Celsius indicate optimal environmental parameters during fermentation. The fact that
different fermentation temperatures give different results, bakers utilizes them according to their
need. With the change in fermentation temperature, the proportions of lactic acid and acetic acid
also change. As a result of this, different flavors and physical characteristics are achieved. So if
fermentation temperature is increased to 27 degree Celsius, there will be a noticeable boost in
lactic acid production.
The high content of lactic acid in bread makes taste fuller in the mouth as the crust becomes
thinner, crispier and more crumbs (Wehrle, Grau and Arendt, 1997). Whereas lower temperature
of 22 degree Celsius, not affecting acidic acid levels, drops lactic acid level and eventually
astringent, tighter and sharper flavor is achieved. Higher levels of acetic acid, on the other hand,
results in tighter crumbs with thicker, less crispy and chewier crust (Seguchi, Hayashi and
Matsumoto, 1997).
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:

Intermediate proof also known as benching or bench time, refers to a period of rest between
rounding and final shaping of the dough. Meanwhile, the dough temperature becomes evenly
distributed. Benching is done for making dough sufficiently soft and extensible. An intermediate
proof allows carbon dioxide generation even more, and the gas bubbles begin to increase the size
of the dough. So, this period is critical for influencing the structure of the final product. The
temperature of this period is needed to be consistent with temperature during primary
fermentation. Then there is a formation of an open cellular structure with gases trapped in
pockets.
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.

The proper amount of water and its temperature are the main factors for the formation of a
protein called Gluten in the dough. The minerals (calcium and magnesium) contained in water
help proteins in the dough to bind more tightly and form stronger gluten structure (Wang,
Oudgenoeg, van vilet and Hamer, 2003). So when flour is mixed with water, the gluten starts
swelling to form a network of fine strands making the dough elastic and extensible. This network
is responsible for the texture of the bread because of some important properties of gluten – twice
as much absorption of weight in water, sticky, extensible and highly elastic. So by these
properties, the dough strength increases, gets good structure and shape, an extension of shelf life,
increased softness as well as enhanced flavor. Gluten is formed by the hydration of Gliadin and
Glutenin proteins. Further, gluten oxidizing agents such as Ascorbic acid stimulate the formation
of more bonds and hence strengthening the dough. Too weak gluten does not enable the dough to
stretch thinly around the air bubbles formed during the fermentation process. Then they swell
and burst causing the dough to lack volume. Conversely, the strong gluten doesn’t stretch too
much so the gas bubbles won’t expand and burst to make the loaf much denser.
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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