- Acidity; total acidity; organic acid(s)
Those organic compounds which register as acidic are called organic acids, and these comprise almost all the acids found in seishu. 73% of sake acids are produced by yeast during the main fermentation, with about 17% coming from shubo, and the remaining 10% from steamed rice and koji.
Organic acids are important components of sake taste, giving acidity (sourness) and umami, with volatile acids also contributing to aroma. In order of volume, there is most succinic acid, followed by malic acid, lactic acid, citric acid and acetic acid. In moromi, succinic acid is produced in the greatest amounts, followed by malic acid, then lactic acid. At the yeast starter stage, most lactic acid is produced, followed by acetic acid and succinic acid.
When sake is pasteurized, succinic acid and malic acid decrease, and lactic acid increases. When sake is contaminated, we see a rise in levels of acetic acid and lactic acid, whereas levels of malic acid and citric acid decrease.
It is permitted to use lactic acid, malic acid and succinic acid to adjust a mash or product with insufficient acidity (hosan, 補酸), and lactic acid, succinic acid, citric acid and malic acid may be used as auxiliary materials.
Fractional determination of the various acids in sake is difficult, so the sample of seishu is usually directly titrated with alkaline solution to measure total acidity. Using a combination indicator (kongo (long second ”o”) shiji-yaku 混合指示薬) made with bromothymol blue (BTB) and neutral red (NR) indicators, the number of ml of 0.1N-NaOH alkaline solution (arukari-eki アルカリ液) required to neutralize 10ml of sake is given as the level of acidity.