Water Activity

Novasina - Water Activity

The water activity is given as the aw – value and ranges between 0 (absolute dryness) and 1 (condensed humidity). Only this component takes an active part in the exchange with the ambient humidity and can possibly form the ideal medium for microbiological growth on the surface which influences the microbiological stability. Water activity also has an important effect on the chemical reactions in food.

The relative humidity is measured after reaching the equilibrium humidity over a sample (partial water vapor pressure) The relative humidity is measured in % RH and relates to the aw–value as follows: aw = ERH/100

The influence of water activity in foods

The humidity balance value of a product, which is ascertained through its partial the pressure of water vapor on the surface depends, on the following factors:

  • chemical compound
  • temperature
  • water content
  • storage conditions (T / RH)
  • absolute pressure
  • packing

“Free” water in products is jointly responsible for the growth of undesirable organisms such as bacteria or fungi, which produce “toxins” or other harmful substances. But also chemical/biochemical reactions (e.g. the Maillard reaction) increasingly take place and possibly change the following factors of a product:

  • Microbiological stability (growth)
  • Chemical stability
  • Content of proteins and vitamins
  • Colour, taste, and nutritional value
  • Stability of the compound and durability
  • Storage and packing
  • Solubility and texture


Bakery Products
Cosmetics & Personal Care
Dairy Products
Meat & Fish
Powder & Spices


Water Activity Buyers Guide – Verification
Water Activity Buyers Guide – Maintenance
Water Activity Buyers Guide – Accuracy
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