Biological Leavening

The use of yeasts in food processing is prehistoric in origin. Baking, brewing, and wine-making all depend on the ability of yeasts to carry out anaerobic fermentation of sugars, yielding C02 and ethanol. In brewing and wine-making, alcohol is the prime product of interest; in baking, the leavening effect of C02 and ethanol is more important. In this article only the leavening action of yeast in baked goods is discussed.

Oven Spring

The use of yeast in bread production gives a product containing many small gas cells—leavened bread. By the end of the proofing period the aqueous phase of the bread is saturated with C02 and the volume has roughly doubled owing to the pressure of C02 that has diffused to air cells or bubble nuclei. During the first part of the bake cycle the loaf expands; then at some temperature the matrix sets, expansion stops, and the rest of the baking time is for the purpose of starch gelatinization, crust coloring, flavor development, and so on. The increase in loaf volume during baking is called oven spring (16). The magnitude of oven spring depends on two factors: (1) generation and expansion of gases; and (2) the amount of time available for loaf expansion before the structure sets. The first factor is primarily a function of yeast fermentation; the second one is affected by dough components such as shortening, surfactants, gluten protein, and flour lipids.

The influence of several dough components on finished volume has been explored (17,18). A key observation is shown in Figure 2 (18,19). Dough with or without shortening expands at the same rate initially, but at 55°C the structure of the fat-free dough begins to set, slowing the expansion rate. In the presence of 3% shortening, dough

Dough temperature (°C) 55 80

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Dough temperature (°C) 55 80

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Sleeping Sanctuary

Sleeping Sanctuary

Salvation For The Sleep Deprived The Ultimate Guide To Sleeping, Napping, Resting And  Restoring Your Energy. Of the many things that we do just instinctively and do not give much  of a thought to, sleep is probably the most prominent one. Most of us sleep only because we have to. We sleep because we cannot stay awake all 24 hours in the day.

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