Amino sando・amino san
- Amino acidity (level of amino acids); amino acid(s)
“Amino acid” is the common name for a group of organic compounds that have the functional groups of both amino and carboxyl groups. In its narrow sense, the word indicates α-amino acids, which are the building blocks for protein in organic life forms.
The amino acids in seishu exist in the form of salts, and (together with lower peptides) displaying slight sweetness, umami, acidity and bitterness, are constituents of sake flavour. Where amino acid levels are too high, the sake is hard to drink with high levels of zatsu-mi off-flavour. When amino acid levels are low, the sake will be thinner and kirei (“clean”). Primary examples of amino acids include glutamic acid, glycine, alanine, valine, arginine and so on. Monosodium glutamate is sometimes used as an auxiliary material.
The National Tax Agency’s Method of Analysis adopts formol titration to measure amino acids. This works by condensing amino groups with formaldehyde in a neutral or slightly alkaline solution to make compounds of dimethylol or monomethylol, then measuring free carboxyl groups. After neutralizing 10ml of sake, formaldehyde is added, and the number of ml of 0.1N-NaOH required to neutralize the freed carboxyl groups by titration is given as the level of amino acids.
The average range of amino acids in sake is from 1.0 – 2.0. Light examples with a value of less than 1.0 can be said to be tanrei (淡麗, light) sake, low in amino acids. Sake with high levels of amino acids at more than 2.0 will be full-flavoured sake, often described with the adjective (濃醇 noujun; tanrei and noujun may be considered opposites).