- Solubility of rice
The “solubility” of rice generally refers to the ability of steamed rice to be “digested” (dissolved) by enzyme preparations. In Japanese, this important piece of brewing information is expressed with the verb 溶ける (tokeru, to melt or dissolve) – 溶かす(tokasu) in its transitive form. When white rice is steamed and dissolved by exposure to enzymes, the rate and degree at which it is consumed varies according to the rice variety. By looking at this, it is possible to some extent to predict how the particular rice will dissolve in the moromi mash.
When sakamai is studied in Japan, 10g of white rice first undergoes soaking, draining, and steaming under fixed conditions. Then, after the rice has been digested for twenty-four hours at 15°C in a buffer solution containing amylase, the filtrate is measured for sugar content (in degrees Brix) and for formol nitrogen. The measurement of formol nitrogen uses the same principle as for the measurement of the level of amino acids in seishu. Amino acids are condensed with formaldehyde under neutral or slightly alkaline conditions, and the carboxyl groups then liberated are measured by acidimetry.