Bread is one of the most ancient of human food and is produced with the help of microorganisms. In bread production, yeast is growing under aerobic conditions. This results in increased CO2 production and minimum alcohol accumulation. The fermentation of bread consists of several steps – alpha- and beta- amylases present in the moistened dough release maltose and sucrose from starch.
Then a baker’s yeast Saccharomyces cerevisiae, which contains maltase, invertase and zymase enzymes, is added. The CO2 produced by the yeast results in the light texture of many types of bread and traces of fermentation products contribute to the final flavour.
The basic ingredients in bread-making are flour, water, salt and yeasts. In modern bread making however a large number of other components and additives are used in the baking process. These include yeast, proteins, carbohydrates, fat emulsifiers, sugar, milk, eggs, antifungal agents, anti-oxidants, enzymes, flavoring and enriching ingredients. The ingredients are mixed together to form the substrate for bread production called dough which is then baked.
The most common starting material for most bread is wheat flour. Breads are also commonly made from a wide variety of other cereal grains, including rye, barley, oats, corn, sorghum and millet. Gluten a protein complex that gives bread its structure and elasticity and is necessary for the leavening process is poorly formed or absent in most non-wheat flours.
The specific composition of flour is critically important because it has a major influence on the fermentation and physical structure of the dough and finished bread. Wheat flour is the primary ingredient in most bread. The most important flour used for bread manufacture is refined white flour. It consists of two main components—protein and carbohydrates especially starch with a small amount of hemicellulose and lipid.
About 8% to 15% of wheat flour is protein. Protein content dictates the use of that flour. High protein flours generally contain more than 11% protein and are best used for bread. Low protein flours contain 9% or less protein and are most often used for cakes, cookies and pastries. The protein provides the support matrix necessary to retain the carbon dioxide made during fermentation. Therefore, protein content has a major impact on dough expansion and loaf volume in bread making.
The most important protein fractions are gliadin and glutenin, which account for 85% of the total protein. When gliadin and glutenin are hydrated and mixed, they form complex called gluten, which is a key component of bread dough. The remaining proteins (15% of the total) consist of other globulins and albumins. Several enzymes such as alpha and beta amylase play an important role.
Carbohydrates are the main fraction of flour, constitutes up to 75% of the total weight. This fraction is largely comprised of starch and small amount (about 1%) of simple sugars, cellulose and fiber. The main carbohydrate component is starch, which consists of amylose, and α -1, 4 glucose linear polymer (about 4,000 glucose monomers per molecule) and amylopectin, an α -1, 4 and α – 1, 6 glucose branched polymer (about 100,000 glucose monomers per molecule).
About 20% to 25% of the starch fraction is amylose and 70% to 75% is amylopectin. In its native state wheat starch exists in the form of starch granules. The amylose and amylopectin are contained within these spherical granules in a rigid, semi crystalline network. Native starch granules are insoluble and resist water penetration. However, some of the starch granules (3% to 5%) are damaged during milling, which enhances absorption of water and exposes the amylose and amylopectin to hydrolytic enzymes, such as alpha-amylase.
Water is the second largest ingredient of bread after flour. It is used in bread making to provide hydration of the dry ingredients. Hydration of the dry ingredients is important because the combination of water with gliadin and glutenin will produce the gluten network. Water also will act as solvent and dispersing agent for other ingredients like salt, sugar, milk and others.
The amount of water presence would influence the extensibility of the dough. Sufficient amount of water could lead to soft and sticky dough. Insufficient water would cause formation of tough dough that could not be stretch. Excessive amount of water make the dough too sticky and difficult to handle and further results the bread becoming wet, soggy and susceptible to microbial spoilage.
Amount of water and temperature of water used in straight and sponge dough method are not the same. The amount used in the sponge dough method is higher compare to water used in straight dough method. It is because the sponge dough method needs extra water to mix the sugar and the yeast for the sponge making step.
Water used in straight dough method is cold water. While the water used for sponge dough method is normal distilled water because the mixing time of the straight dough method is longer than the other one. So, the temperature produced during mixing will be reduced.
Yeast is the leavening agent used in bread making. The active yeast will show its property by producing bubbles when it mixed with water. This property only showed by instant dry yeast. The other type of yeast does not show this property because they are already in the wet form.
The active dry yeast can be used directly without needed to activate. Yeast will produce the carbon dioxide, the gas that form when the yeast ferment. The carbon dioxide produced is trapped in the gluten network thus make the dough expand in the oven. Thus, the fermentation of yeast helps to give bread its desirable volume.
The temperature needed to be control along the processing line because excess heat supplied will make the yeast over ferment that will produce bread with yeasty smell. The yeasts used for baking are strains of Saccharomyces cerevisiae.
The ideal properties of yeasts used in modern bakeries are as follows:
(i) Ability to grow rapidly at room temperature of about 20-25°C.
(ii) Easy dispersability in water.
(iii) Ability to produce large amounts of CO2 rather than alcohol in flour dough.
(iv) Good keeping quality, i.e. ability to resist autolysis when stored at 20°C.
(v) Ability to adapt rapidly to changing substrates are available to the yeasts during dough making.
(vi) High invertase and other enzyme activity to hydrolyze sucrose to higher glucofructans rapidly.
(vi) Ability to grow and synthesize enzymes and coenzymes under the anaerobic conditions of the dough.
(vii) Ability to resist the osmotic effect of salts and sugars in the dough.
(viii) High competitiveness, i.e. high yielding in terms of dry weight per unit of substrate used.
The sugar used in the bread making will act as the food supply for yeast. The residual sugar after the yeast fermentation will used to contribute to the crust color due to the caramelization and browning reaction. The sugar used is brown sugar due to its smell very good compared to the common sugar.
The brown color will make the crust slightly nicer. The sugar also provides sweetness to the bread to improve the taste of the bread. The sugar may longer the shelf life of the bread because it can bind to the free water in the bread to reduce the water activity and thus reduce the ability of the microbial growth in the bread. Excess sugar in the dough will decrease the fermentation rate as the yeast competes with sugar for the water present in the dough. The yeast action become slow and the dough will not rise.
Salt provides flavor to the bread. Salt-free bread rises quickly, while too much salt can reduce or destroy yeast action. It helps control yeast development and prevents the bread from over rising. This contributes to good texture. It may affect the rate of yeast activity if wrong processing step applied. About 2% sodium chloride is usually added to bread.
It serves the following purposes:
(i) It improves taste.
(ii) It stabilizes yeast fermentation.
(iii) Provide toughening effect on gluten.
(iv) Helps retard proteolytic activity, which may be related to its effect on gluten.
(v) It participates in the lipid binding of dough.
Due to the retarding effect on fermentation, salt is preferably added towards the end of the mixing. For this reason flake-salt which has enhanced solubility is used and is added towards the end of the mixing.
Egg also used in bread making. It gives foam to bread that may help to retain the air bubbles which can act as the nucleation site for the carbon dioxide gas produced by fermentation. Thus, it acts as leavening agent. Egg also gives texture, flavour and color to the bread.
Milk powder added in bread making as the nutritional supply to increase the amount of protein, carbohydrate and minerals. Milk is added to make the bread more nutritious, to help improve the crust color, presumably by sugar caramelization and because of its buffering value.
Lactose sugar caramelization from milk powder also may help sugar in producing brown color of crust by the browning reaction. Milk powder also helps to strengthen the dough due to the presence of protein and calcium. The pH of the dough is buffered by the addition of milk. This will retard the fermentation and may avoid the over fermentation of yeast.
Animal and vegetable fats are added as shortenings in bread- making at about 3% (w/w) of flour in order to yield – (a) increased loaf size; (b) a tenderer crumb and (c) enhanced slicing properties.
Emulsifiers are used in conjunction with shortening and ensure a better distribution of the latter in the dough. Emulsifiers contain a fatty acid, palmitic, or stearic acid, which is bound to one or more poly functional molecules with carboxylic, hydroxyl and/ or amino groups, e.g. glycerol, lactic acid, sorbic acid, or tartaric acid. Sometimes the carboxylic group is converted to its sodium or calcium salt. Emulsifiers are added as 0.5% flour weight.
A proper content of amylolytic enzymes must be present during bread-making to breakdown the starch in flour into fermentable sugars. Since most flours are deficient in alpha-amylase flour is supplemented during the milling of the wheat with malted barley or wheat to provide this enzyme.
Fungal or bacterial amylase may be added during dough mixing. Bacterial amylase from Bacillus subtilis is particularly useful because it is heat-stable and survives the baking process. Proteolytic enzymes from Aspergillus oryzae are used in dough making, particularly in flours with excessively high protein contents.
The spoilage of bread is caused mainly by the fungi Rhizopus, Mucor, Aspergillus and Penicillium. Spoilage by Bacillus mesenteroides (ropes) rarely occurs. The chief antifungal agent added to bread is calcium propionate. Others used to a much lesser extent are sodium diacetate, vinegar, mono-calcium phosphate and lactic acid. Bread is also often enriched with various vitamins and minerals including thiamin, riboflavin, niacin and iron.
The large scale production of bread consists of following steps:
(i) Pre-Fermentation or Sponge Mixing:
At this stage, a portion of the ingredients is mixed with yeast and with or without flour to produce an inoculum. During this the yeast becomes adapted to the growth conditions of the dough and rapidly multiplies. Gluten development is not sought at this stage.
The remaining ingredients are mixed together with the inoculum to form the dough. During this step maximum gluten development is achieved.
The dough formed above is cut into specific weights and rounded by various equipments and machine.
The dough is allowed to keep for about 15 minutes at the same temperature as it has been previous to this time, i.e. at about 27°C. This is done in equipment known as an overhead proofer.
The dough is flattened to a sheet and then moulded into a spherical body and placed in a baking pan which will confer shape to the loaf.
This consists of holding the dough for about 1 hour at 35-43°C and in an atmosphere of high humidity (89-95°C).
During baking the proofed dough is transferred, still in the final pan, to then oven where it is subjected to an average temperature of 215-225°C for 17-23 minutes. Baking is the final step of the bread making processes. It is the point at which the success or otherwise of all the previous inputs is determined.
The bread is depanned, cooled to 4-5°C sliced and wrapped in waxed paper or plastic bags.
(ix) Leavening of Bread:
The events taking place in dough during primary fermentation before the dough is introduced into the oven may be summarized as follows. During bread making, yeasts ferment hexose sugars mainly into alcohol (0.48 gm), carbon dioxide (0.48 gm) and smaller amounts of glycerol (0.002-0.003 gm) and trace compounds (0.0005 gm) of various other alcohols, esters aldehydes and organic acids.
The CO2 dissolves continuously in the dough, until the latter becomes saturated. Subsequently, the excess CO2 in the gaseous state begins to form bubbles in the dough. The formation of bubbles which causes the dough to rise or to leaven. The total time taken for the yeast to act upon the dough varies from 2-6 hours or longer depending on the method of baking used.
The most important factors which influence the leavening of bread by yeast include:
(1) The nature and availability of the sugar,
(2) Osmotic pressure,
(3) Effect of nitrogen and other nutrients,
(4) Effect on fungal inhibitors, and
(5) Concentration of baker’s yeasts.
Leavening is the increase in the size of the dough induced by gases during bread-making.
Leavening may be brought about in a number of ways:
(i) Air or carbon dioxide may be forced into the dough but this method is a good one.
(ii) Water vapor or steam which develops during baking has a leavening effect. This has not been used in baking; it is however, the major leavening gas in crackers.
(iii) Oxygen has been used for leavening bread. Hydrogen peroxide was added to the dough and oxygen was then released with catalase.
(iv) It has been suggested that carbon-dioxide can be released in the dough by the use of decarboxylases, enzymes which cleave off carbon dioxide from carboxylic acids. This has not been tried in practice.
1. Leavening by Chemicals:
The use of baking powder has been suggested. Baking powder consists of about 30% sodium bicarbonate mixed in the dry state with one of a number of leavening acids, including sodium acid pyrophosphate, monocalcium phosphate, sodium aluminum phosphate, monocalcium phosphate, glucono-delta-lactone.
CO2 is evolved on contact of the components with water – part of the CO2 is evolved during dough making, but the bulk is evolved during baking. Baking powder is suitable for cakes and other high-sugar leavened foods, whose osmotic pressure would be too high for yeasts. Furthermore, weights for weight yeasts are vastly superior to baking powder for leavening.
2. Leavening by Microorganisms:
These processes may be done by any facultative organism releasing gas under anaerobic conditions such as heterofermentative lactic acid bacteria, including Lactobacillus plantarum or pseudolactics such as Escherichia coli. In practice however, yeasts are used; even when it is desirable to produce bread quickly such as for the military or for sportsmen and for other emergency conditions the use of yeasts recommends itself over the use of baking powder.
There are three basic systems of baking:
(1) Sponge dough method
(2) Straight dough method, and
(3) The liquid ferment method.
All three are essentially similar .and differ only in the presence or absence of a pre-fermentation. Where pre-fermentation is present, the formulation of the pre-ferment may consists of a broth or it may be a sponge (i.e., includes flour). All three basic types may also be batch or continuous porous.
In this method, the mixture of sugar, yeast and water was fermented for 10 minutes in a proofer. The temperature of proofer controlled as well as the other steps to avoid over fermentation of yeast. The temperature of proofer is maintained at 25.5-27°C with relative humidity. In controlling the humidity of the proofer, a pan with an amount of water was put inside.
The yeast reacts with sugar accordingly to equation below:
C6H12O6 + Yeast → 2CO2 + 2C2H5OH
The fermented yeast was mixed with the dry ingredients. The difference of this method compared to the straight method is that the dough produced after the mixing by using sponge dough method is stickier and looks like need to add flour. This is the common thing happen in sponge dough method because the dough contains higher amount of gas bubbles inside the dough. The retention of more gas is good in producing smooth bread.
In the mixer, the dough said to knead, whereby it involves pushing and pulling the dough to stretch and strengthen the gluten in the dough. Gluten gives bread structure; it consists of strands of protein that form when water is added to flour. The protein stretches to accommodate the bubbles produced during fermentation, allowing bread to rose.
Both of the dough produced after mixing is proof again in the proofer. This is the second proofing for sponge dough method while for straight dough method this is the only proofing involve. Proofing for this time takes about 30 minutes. Basically the dough will expand two times of its initial volume.
After 30 minutes the dough took out from the proofer. The dough was punched manually by hand. The expanded dough then becomes compressed back. This step is important in distributing the gas in the dough. If the punching does not done, a big hole of gas will be formed containing the gas from fermentation of yeast.
The dough then weighted to divide it into several portion. When dividing, be sure to use a sharp knife or kitchen shears, as tearing it will compromise the gluten. Whether or not dough is divided, it should be roughly reshaped and allowed to rest, covered, for 20 minutes after the second proofing.
This will help produce the most evenly shaped loaf. Shaping is important to produce a nice looks of the product. Different types of bread require different shaping. The shaping done by rolling the dough and then roll it downward forming a long shape. The side of the dough pulled inward at the down side of the dough.
The folding work need to be done carefully. The complete shaping dough put into a pan and the pan should be grissed with shortening first to avoid the bread produced stick to the pan. The pans with the dough will be ferment again for 30 minutes.
After 30 minute, the dough is ready to be baked. The baking takes 20-25 minutes with a temperature of 180°C. Baking is done to gelatinize or to cook the dough to achieve good volume and attractive crust. The bread was cooled to room temperature and further analysis on other parameters can be carried out.
The Straight dough begins with the mixing of yeast, sugar and water. This step was done to activate the dry instant yeast. The yeast mixture produce bubbles in a few minutes mixing. The other dry ingredients mix together in the mixer, except shortening and salt.
After the dry ingredients mix together, yeast and water are added then followed by the shortening and salt. The two ingredients are added at the last step, because it may inhibit the gluten network if added earlier. The interfering of salt and shortening to the gluten network may produce the bread with low volume and compressed bread.
In this system water, yeast, food, malt, sugar, salt and milk are mixed during the pre-fermentation at about 30°C and left for about 6 hours. After that, flour and other ingredients are added in mixed to form dough.