Moisture
Japanese: 水分
The amount of water in a food product. Essential for microbial activity, moisture levels determine fermentation speed and safety.
Moisture is essential for microbial activity. Without water, enzymes cannot function, nutrients cannot dissolve, and microorganisms cannot grow.
Miso's moisture content is approximately 44–48%. This figure is not accidental but a deliberately designed formulation for proper fermentation. Too much moisture invites contamination; too little halts fermentation.
Even more critical is the concept of water activity (Aw). Not all water in food is available to microorganisms—only 'free water,' unbound by salt or sugar, supports microbial activity.