Osmotic pressure
Japanese: 浸透圧
The force that drives water from a dilute solution to a concentrated one across a semipermeable membrane. The preservation principle behind salting and sugaring.
Osmotic pressure is the phenomenon where water moves from a dilute solution to a concentrated one when separated by a membrane.
When you salt vegetables and water emerges, that's osmotic pressure at work. In a high-salt environment, moisture is drawn from microbial cells too. Most contaminants cannot survive this dehydration, but salt-tolerant yeasts and certain lactic acid bacteria endure.
Miso and soy sauce ferment safely within this 'salt barrier' because osmotic pressure selectively controls which microorganisms can thrive. Salt doesn't just add flavor—it acts as an invisible filter, sorting microbes.