It is unknown how much food waste occurs during food processing. When food is stored, considerable amounts are wasted because of pests and microorganisms. This problem occurs in countries where it is both relatively hot, and humid. These conditions boost the growth of pests and microorganisms. Extreme temperature, humidity, or microoganisms also influence the nutritional value, caloric value and edibility of crops and account for food waste. The "qualitative losses" are more difficult to assess than quantitative ones. More losses occur because the food is not handled correctly, or because it loses weight or volume.