Wet-and-dry-bulb thermometer (psychrometer)

A wet-and-dry-bulb thermometer (psychrometer) is an instrument used to measure temperature and humidity, and it plays an important role in the sake brewing process. It uses two thermometers: one is an ordinary dry-bulb thermometer, and the other is a wet-bulb thermometer wrapped in moistened gauze. The dry-bulb thermometer shows the air temperature, while the wet-bulb thermometer shows a temperature affected by humidity. The difference between the two readings is called the "wet-dry difference" (kanshitsusa), and it can be used to calculate relative humidity. In sake brewing, it is used mainly to manage humidity in the koji room (koji muro), which is very important for encouraging proper fermentation. Maintaining relative humidity within the appropriate range contributes to improving the quality of the sake.