All microorganisms must have an abundant supply of water to grow. Perishability of a food is related to the moisture content, and the water activity level.
Microorganisms that need oxygen (air) to grow are called aerobic.
The degree of acidity or alkalinity (base) of a substance is measured by its pH. pH is measured on a scale from 0 to 14.0. An environment with a pH of 7.0 is exactly neutral. Foods with a pH below 7.0 are acidic; a pH above 7.0 is alkaline. The lower the pH, the higher the acidity; the higher the pH, the lower the acidity.