Role of Yeast in baking

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Role of Yeast in baking

Yeasts are eukaryotic ,single celled microorganisms classified as members of the fungus kingdom. Yeasts are unicellular organisms that evolved from multicellular ancestors with some species having the ability to develop multicellular characteristics by forming strings of connected budding cells known as pseudo hyphae or false hyphae. The scientific name of yeast is Saccharomyces cerevisiae. Yeast, as other living organism ,requires supportive environment.

Adequate moisture
Moderate temperature
Mildly acidic conditions
Fermentable carbohydrates
Essential minerals

Yeast brings about changes in the dough during fermentation:

Fermentable matter gets used up
Waste products get accumulated around the cells, carbon di oxide, alcohol, acids and esters .
Rise in temperature
Modification of Ph conditions
Mellowing of gluten.

Yeast grows in dough fermentation. The longer the fermentation time, the more is the growth. Thus, for long fermentation processes, a lesser quantity of yeast is needed for same effect on bulk dough. When yeast is first added to dough,it is in a somewhat dormant state, due to storage in refrigerated condition. Although gas may start to evolve, yeast may take up to 45 minutes of ideal conditions to get fully active to fermentation .

Sometimes it is useful to separately make a slurry of yeast in warm water, with sufficient carbohydrates and mineral food before mixing with flour. It is essential to control factors which are known to inhibit yeast activity at initial stages. Thus salt ,mold inhibitors ,shortening and high level of sugar are held back in early stages of fermentation ,and added at second stage.

This is called knock back .During second mixing ,the waste material is disturbed from around yeast cells, fresh air and foods are brought closer, and temperature is equalised.

Other things being equal ,yeast activity is substantially improved with availability of water. Soft sponges, and slurries show better yeast activity compared to stiffed doughs.