Moisture is essential to all living organisms, but during composting, moisture is lost by evaporation. The compost cools to prevent overheating, but care must be taken to ensure that the compost does not dry out too quickly. The optimum moisture content for composting is generally 50–60% (wet weight basis). Below about 30%, microbiological activity is severely restricted. Above about 60%, compost can become anaerobic and odorous.