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Multiple parallel fermentation: Japanese Sake


Among the various kinds of alcoholic beverages, sake in particular is said to require a high level of technical skill to make. This is very much related to the method of production.


In making sake, both saccharification (conversion of starch to grape sugar) and fermentation take place in the same vat. Because of this, small variations in the equilibrium of the mixture can result in large differences in the taste of the final product.


Why multiple parallel fermentation is necessary
By means of fermentation with yeast, sugar turns into alcohol. Alcoholic beverages produced by this method are called brewed liquors. Examples are wine, beer, and sake.


In the case of wine, the sugar in grapes is fermented by means of yeast. The yeast is added directly to the grape juice once it is squeezed from the grapes. This is referred to as simple fermentation.


In beer, the ingredient that is fermented is barley, which contains starch. Because alcohol cannot be made from starch, it is first necessary to convert the starch to maltose (malt sugar) using malt. Subsequently, when yeast is added, the maltose turns into alcohol.


In this way, beer is produced, but the two stages are separate. That is, the two transformations, “barley (starch) → maltose” and “maltose → alcohol” take place in separate vats. This is termed “multiple sequential fermentation.”


In making sake, it is starch-containing rice that is fermented, just as, with beer, starch-containing barley is fermented. Therefore, it is first necessary to convert the starch to grape sugar. The kōji-kin mold is used to make sugar from starch. After that, the sugar is turned into alcohol with the help of yeast.


The big difference between making beer and making sake is that, with sake, the two processes “starch → grape sugar” and “grape sugar → alcohol” take place in a single vat.


That is to say, after starch is converted to grape sugar, the conversion from grape sugar to alcohol starts immediately. This is what is known as “multiple parallel fermentation.” Multiple parallel fermentation is a production method that is peculiar to sake making, and is rarely used anywhere else in the world for making alcoholic beverages.



High alcohol content using multiple parallel fermentation
The alcohol content of sake can be as much as 20%. This relatively high figure is due to the fact that as soon as grape sugar is produced through the action of the kōji-kin, it is converted to alcohol by the kōbo (yeast). In multiple parallel fermentation, because the yeast is available as soon as sugar is produced, the conversion to alcohol is very efficient.


This is quite different from other brewed liquors like wine and beer, where yeast is added to a liquid that already contains a large amount of sugar to initiate fermentation.


Doing things this way, it would require a very high sugar content to achieve 20% alcohol content. Moreover, with this sort of liquid, the yeast could not do its job properly due to the high sugar content, so a satisfactory result can not be achieved.


Because of the unique method used in making sake, it is possible to achieve an alcohol content as high as 20% without concentration of the liquor as in distillation techniques. It can also be said that the multiple parallel fermentation used in making sake is, among the various fermentation techniques used throughout the world, the most technically complex.

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