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Food Science & Technology vocabulary · Food Chemistry and Composition

Water activity

Meaning in food science & technology, with examples

nounCore term

In food science & technology, water activity means: A measure from 0 to 1, written aw, of how much of the water in a food is free for microorganisms and chemical reactions; pure water has a value of 1.0.

In Turkish: su aktivitesi

How it is used

One of the most important numbers for shelf life and safety. Most bacteria cannot grow below about 0.90, many molds still grow around 0.80, and almost no microbe grows below 0.60. It is measured with a water activity meter and lowered by drying or by adding salt or sugar. It is not the same as moisture content.

Example sentences

  1. The dried apricots have a water activity of 0.65, so they are stable at room temperature.

  2. Adding more sugar lowered the water activity of the filling and solved the mold problem.

Common collocations

  • low water activity
  • measure water activity
  • water activity meter
  • reduce water activity
  • aw value
  • moisture contentThe amount of water in a food, usually given as a percentage of its weight and measured by drying a sample and weighing the loss.
  • dryingRemoving water from food, usually with heat and moving air, to lower its water activity so that microorganisms cannot grow and the product keeps for a long time.
  • moldA type of fungus that grows as fuzzy threads on food surfaces; it causes visible spoilage, and some types produce harmful toxins called mycotoxins.
  • shelf lifeThe length of time a food stays safe and keeps its expected quality when it is stored under the stated conditions.
  • pHA scale from 0 to 14 that shows how acidic or alkaline a food or solution is; 7 is neutral, lower values are acidic and higher values are alkaline.

More terms: Food Chemistry and Composition

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