A deeper dive into the details of parallel fermentation.
The chemical formula of starch is (C6;H10;O5) and it is a polysaccharide, (i.e, a carbohydrate that has multiple sugar molecules combined together). Yeast doesn't have the ability to break down starch because it doesn't contain the enzyme Amylase, the enzyme that is found in Koji mold (Aspergillus oryzae S). This enzyme breaks down the multiple molecules into monosaccharides so that they are able to be ingested by the yeast fungus to create the ending result of alcohol, hence the phrase "Parallel Fermentation".
In the early beginnings of Sake, brewers were able to break down the polysaccharides from the starch that came from rice with the use of saliva, yes spit, you read that right. How this became a thing I will never know. Amylase is located in your saliva and in your pancreas. So before that fateful accidental discovery of Koji mold growing on the rice supply, spit was used as one of the main ingredients in making Sake. It was most likely verified later through conformational experimentation and probably accidental chance that Aspergillus oryzae S. breaks down the polysaccharides into multiple monosaccharides faster and easier than spitting into a bucket of rice.
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