In breadmaking, microorganisms are useful in two primary ways: (1) they can produce gas to leaven the dough, giving it the desired loose, porous texture, and (2) they can produce flavorful substances. They may also play a role in dough conditioning.

Leavening 

• Bread yeasts typically leaven dough by fermenting the dough’s sugars to create primarily carbon dioxide and alcohol.
• For leavening, however, additional actively gas-forming microorganisms such as wild yeasts, coliform bacteria, saccharolytic Clostridium species, heterofermentative lactic acid bacteria, and other naturally occurring combinations of these organisms have been utilised.
• Additionally, leavening can be achieved through the direct insertion of gas (CO2) into the dough.

Leavening by Bread Yeasts 

• There is little or no growth during the first two hours after the yeast is added to the dough, assuming that much time is allowed before baking, followed by a reduction in growth over the next four to six hours.
• The dough (or sponge) begins to ferment as soon as the yeast is added and continues until the heat of the oven deactivates the yeast enzymes.
• The skilled baker uses a substantial quantity of yeast and a relatively brief baking period.
• The current tendency in home baking is to use an excessive amount of yeast so that the fermentation time is even shorter than in professional baking.
• These quick techniques promote minimal or no yeast growth during the fermentation process.
• Using less yeast or yeast that was less effective resulted in a longer production time and the potential for yeast and bacterial growth using older home methods.
• “Conditioning” of the dough occurs during fermentation when the flour proteins (gluten) develop, i.e., become elastic and springy and thus capable of storing a maximum quantity of the carbon dioxide produced by the yeasts.
• The gluten is conditioned by the activity of (1) proteolytic enzymes in the flour derived from yeast, malt, or other additives, and (2) the pH-lowering effect of the added and produced acids.
• Dough conditioners, often known as yeast meals, consist of ammonium salts to activate yeasts and different salts, such as KBrO3, KIO3, CaO2, and (NH4)2S2O8, to improve dough properties.
• Although the sugar in the flour and the sugar produced by the flour amylase may be sufficient for yeast fermentation, most recipes ask for the addition of additional sugar or malt containing amylase.
• The rate of gas production by yeasts can be increased by adding (1) additional yeast, (2) malt containing sugar or amylase, and (3) yeast food, within certain restrictions. It is diminished by (1) the inclusion of salt, (2) the addition of an excessive amount of yeast food, and (3) the application of too high or low temperatures.
• The primary aims of the baker during leavening are to produce sufficient gas and to ensure that the dough will retain the gas at the appropriate period.
• In the sponge method of breadmaking, certain components are blended at 23 to 24 degrees Celsius and left to ferment to the required degree of ripeness.
• The remaining ingredients are then added, and the dough is fermented until it reaches the appropriate consistency.
• In the straight-dough method, all components are combined at 26 to 28 degrees Celsius. The fermentation room, where dough is kept for the majority of the leavening process, is typically maintained at a temperature of 27 C.

Leavening by Other Microorganisms 

• Other gas-forming microbes besides bread yeasts are capable of causing fermentation. As with certain specialty breads including sourdough bread, loaves can be leavened with leftover dough from a prior baking.
• The leavening can involve heterofermentative lactic acid bacteria and saccharolytic anaerobes.
• Salt-rising bread is leavened by “salt-rising yeast” and microorganisms present in the ingredients; it may also contain baker’s yeast.
• In other instances, a series of organisms leaven, taste, and change dough, such as in the creation of soda crackers, where a 3- to 4-hour fermentation is followed by the action of lactic acid bacteria.
• Soda-cracker sponge may also be fermented by additional yeast and current bacteria.

Leavening by Chemicals 

• Chemical agents can leaven dough in place of microorganisms, but the product cannot be called bread according to norms of identity that need yeast leavening.
• For leavening, carbon dioxide gas, which can be included directly into the dough, or baking powders, which are mixtures of chemical compounds that release gas when combined with the dough, can be used.
• Since the heat of baking will result in the release of carbon dioxide and ammonium gas, ammonium bicarbonate can be added.
• Self-rising flour contains both the acidic and basic components of baking powder, which react when the flour is hydrated.

Continuous Breadmaking 

• Before the final dough is made, continuous bread-making techniques typically involve the development and fermentation of yeast in a portion of the ingredients to produce a high yield of active yeast, or at least the inclusion of more yeast than usual. Before baking, leavening may take place in the pans.

Flavor Production 

• Yeasts are said to contribute to the flavour of bread through byproducts released during the fermentation of sugars, although the majority of workers feel that yeasts provide little or no flavour, particularly to bread manufactured using modern quick processes.
• Alcohol, acids, esters, and aldehydes are substances that can be used to impart desired flavours. However, most scientists agree that microorganisms living in the dough contribute the greatest flavour.
• In the typical industrial leavening and working procedure, the bacteria do not have enough time to significantly alter the flavour, whereas the longer time available during the traditional techniques of manufacturing at home allows for a significant development of desirable flavours.
• Thus, dough leavened by a prior batch of dough might obtain a healthy inoculum of flavor-producing bacteria.
• Some specific bread brands created in this method are renowned for their distinctive flavours.
• The majority of the taste in bakers’ bread originates from the ingredients and chemical processes that occur during baking, such as Maillard browning.
• If sufficient time is allowed for the growth of bacteria and yeasts prior to baking, both may contribute to the flavour.
• Alcohol, diacetyl, aldehydes, acetoin, and isoalcohols, as well as lactic, acetic, and succinic acids and their esters may be created as flavouring compounds.

The Baking Process 

• Even though the inner temperature of the loaf does not exactly reach 100 degrees Celsius during baking, the heat serves to kill the yeasts, inactivate their enzymes as well as those of the flour and malt, expand the current gas, and set the loaf’s structure. In addition to enhancing the loaf’s appearance, baking imparts desired flavours.
• The heat also drives out most of the alcohol and other volatile molecules produced by the yeasts, but contributes flavor-enhancing compounds such as furfural, pyruvic, and other aldehydes.
• Gelatinization of starch is the most crucial transformation of bread during baking. Gluten provides structural support for the dough, whereas starch provides structural support for the baked bread.

Rye Bread 

• Rye bread can be prepared with or without a “sour” beginning. The traditional method of making sour relied on the naturally occurring bacteria in a mixture of rye flour and water.
• The mixture was fermented for 5 to 10 hours; then extra flour and water were added and fermentation was maintained for another 5 to 6 hours; this process was repeated multiple times.
• Half of the resulting sour was mixed into the bread’s sponge or dough, while the remainder was used to create a fresh sour.
• Some bakers altered this sour by adding yeasts and lactic acid bacteria from cultured buttermilk or Bulgarian buttermilk to a sour that was created everyday.
• Clearly, these sours lack homogeneity. Modern techniques entail the addition of large quantities of acid-forming bacteria cultures to the dough mass used as a sour and the regulation of fermentation time (18 to 24 hours) and incubation temperature (about 25 C).
• A high incubation temperature, such as 32 to 35 degrees Celsius, promotes the growth of unwanted gas-producing bacteria, such as coliform and butyric bacteria.
• Others utilise high-temperature lactics, such as Lactobacillus bulgaricus* and Streptococcus thermophilus, and alter the incubation temperature accordingly.
• Considered beneficial is the growth of heterofermentative lactic acid bacteria. The starter adds a tangy or sour flavour to the rye bread that lactic and acetic acids alone cannot provide.

San Francisco Dough Bread 

• Torulopsis holmii, the asporogenous form of Saccharomyces exiguus, is responsible for the leavening of this kind of bread.
• Lactobacillus sanfrancisco, a heterofermentative lactobacillus, has been identified as the second main organism, responsible for the acid development.