Bacteria need water to grow in food. The perishability of a food is related to the moisture content, and the water activity level. Thus, the drier a food is, the longer it will last. Bacteria cannot grow below 16% water. But the lack of water does not kill them.
Moisture content is the amount of water in food expressed as a percentage. Water activity (aw) is the amount of water available for use and is measured on a scale of 0 to 1.0.
Practical consequence: You can adjust the water content of the food (by eliminating water or by adding compounds that fix the water, such as salt, sugar) to reduce bacterial growth and thus keep longer food.
- Products such as milk powders, dehydrated, or lyophilized vegetables, which have a water content of less than 5%, are no longer subject to bacterial development.
- Table salt or Sodium chloride: Nacl, used in sausages, has an anti-bacterial activity from 20% (in other words, very salty). You then understand why it is challenging to meet the requirements of consumers who want less salty meats.
- Sugar is an excellent preservative from 40%. We find its conservative action in a jam, sweetened condensed milk, etc.
