Total acid 0.56%
Starch and cellulose 16.58%
Water (by difference) 72.16%
The chemical changes which go on in the production of moto are sufficiently easily explained in general terms. During the first days, whilst the mixture is kept at a low temperature, the koji is acted upon by the water and the solution then attacks the starch according to the reactions already indicated. This results in the production of a saccharine and dextrinous liquid forming a suitable food for the ferment which subsequently establishes itself in the liquid on warming. How the ferment appears will be discussed in a later section. Whilst the yeast is growing and converting the sugar into alcohol, the solution of starch and the hydration of dextrin by the koji still continue so long as the latter retains its activity, but that appears to be destroyed some time before the moto is completely finished. At the end of this stage the yeast ferment though not vigorous, is well formed and only requires a fresh addition of food to commence growing with renewed activity. It may, indeed, be said that the preparation of moto has for its main object the production of a healthy ferment, so that the use of the moto in the subsequent operations answers very nearly to the yeast added to the wort in beer brewing.
The sake brewer judges of the progress of the moto by the vigor of the fermentation and by the taste of the liquid. At Itami it is said to require 13 days to obtain the proper taste; after three days the taste is sweet owing to the presence of much dextrose; after six days it is astringent, on the seventh day is slightly alcoholic, and finally, it becomes sour. When finished the brewer is able to distinguish five tastes, respectively sweet, sour, bitter, astringent, and alcoholic, and of these the sour, bitter, and astringent are most pronounced. The formation of the acid is also formed during the time the mash is allowed to cool in the shallow vessels, although its amount cannot be very large seeing the great development which the yeast has taken. The bitter and astringent tastes are due to the presence of the yeast, though the nature of the substances giving rise to them is unknown.
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