In part one I talked about how to measure the Nihonshu-do or Sake Meter Value (SMV) or your sake. In part two I covered how to measure the Arukoru bun (アルコール度数) or Alcohol percent by volume (%ABV). In this part, part three I will discuss how to measure the san-do or acidity of sake.
To measure the san-do (acidity) of sake at home, there are two very closely related methods available. The easier and less expensive of the two methods is to use a wine acidity test kit. This kit contains almost every think you need to measure the acidity on sake. However, there is a difference getting from the physical test to the interpreted value, but I am getting a little ahead of myself. The second method differs from the first in that a pH meter is used rather than Phenolphtalein to determine the point of neutrality. Often the second method employs more sophisticated equipment for each of the components but this is not strictly necessary.
So, what do wine acid test kits come with? Well, they come with a small beaker to mix the sample and chemicals in, a syringe to measure with, a solution of Sodium Hydroxide, usually at a concentration of 0.1 Molarity (M) and Phenolphtalein. The idea behind the test is that we have some unknown amount of acid in our sample that we want to measure. To do this we add a known amount of base to neutralize the sample pH. When we have neutralized the sample pH with a known amount of base we can then work out the original amount of acid. Clear as mud? Perhaps an example will help.