Soy sauce is prepared by fermenting a salted mixture of soybeans and wheat with several microorganisms including yeast over a period of 8-10 months. After the solids are removed, the resulting sauce is rich in lactic acid and ethanol. How aere these 2 compounds produced? In order to prevent the soy sauce from having a strong vinegar taste, oxygen must be kept out of the fermentation tank, why?

how?

Lactic acid and ethanol are produced during the fermentation process of making soy sauce. The microorganisms involved in the fermentation, including yeast and lactic acid bacteria, play a key role in producing these compounds.

1. Lactic acid production: Lactic acid bacteria convert sugars present in the soybean and wheat mixture into lactic acid through a process called lacto-fermentation. These bacteria break down the sugars to produce lactic acid as a byproduct. This contributes to the tangy, sour taste in soy sauce.

2. Ethanol production: Yeast, another type of microorganism in the fermentation process, converts the sugars into ethanol in a process called alcoholic fermentation. Yeast breaks down the sugars into alcohol and carbon dioxide. The resulting ethanol adds depth and complexity to the flavor of soy sauce.

Regarding the prevention of a strong vinegar taste in soy sauce, it is necessary to keep oxygen out of the fermentation tank. This is because exposure to oxygen can lead to a different type of fermentation called aerobic fermentation.

In aerobic fermentation, the presence of oxygen promotes the growth of acetic acid bacteria, which convert ethanol into acetic acid (vinegar) instead of lactic acid. This can alter the taste and aroma of the soy sauce, giving it a strong vinegar flavor.

By maintaining an anaerobic (oxygen-free) environment, the growth of acetic acid bacteria is minimized, allowing the desired lactic acid and ethanol production to occur, resulting in the characteristic flavor profile of soy sauce.