Idli batter fermentation
How does idli batter ferment? Where does the yeast that ferments the batter come from?
ARUNA VENKATRAMAN
Coimbatore, Tamil Nadu
Fermentation is a biochemical process which involves the growth and action of microbes like yeast. With free availability of oxygen, sugars get decomposed into carbon dioxide and water. However, in absence or scant presence of oxygen, the yeast cells consume the sugar in aqueous medium and produce carbon dioxide and alcohol. While the alcohol gets dissolved in the water, the carbon dioxide gas bubbles out. During this process, the thick consistency batters, like that of idli, swell.
The idli batter is prepared by grinding soaked rice and skinned and soaked black gram. Black gram is a legume and is rich in protein; hence it supports microbes like yeast. It is of advantage that there is yeast floating in the air all around us all the time, and some of this yeast will make its way to the sugar/starch rich batters containing sufficient amount of water for the yeast to start growing and dividing.
This yeast is known as the wild yeast. Yeast is a unicellular organism in the class of fungi. On maturing, the cell undergoes multiplication by budding and fission. This process can proceed even while the cells are afloat in the atmosphere where the available moisture helps sustenance of the life form. Thus the air around us has sufficient yeast microbes.
Other similar microbial activities are responsible for infection of injured or dead tissues which provide the supply of both sugar and protein.
Often, the action of the wild yeast is utilised in fermenting beer and special varieties of bread dough; while beer fermentation is carried out in absence of air, the bread batter is fermented in open air.
In fact, in the olden days, when the packaged yeast was not available, the bakers prepared yeast by feeding the wild-yeast in a pot of watery starter dough where the yeast colonies floated up and were regularly harnessed for use. In the case of idli batter, starters are not necessary because the atmospheric wild yeast supply is adequate to ferment the batter overnight to the necessary extent. Of course, during the cold seasons, the fermentation is less effective and so the batter is stored in a warm corner or kept thermally insulated from the surrounding cold environ.
PROF. H. K. SAHU
SCIENTIFIC OFFICER,
INDIRA GANDHI CENTRE FOR ATOMIC RESEAR
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