What is water activity?
Water activity or Aw is the measurement of water vapor pressure generated by free or non-chemically bound water in foods and other products. The Aw value (range: 0.00…1.00 aw) is an important indicator for shelf life of foods, pharmaceutical, and cosmetic products and it strongly influences the occurrence and growth of microorganisms.
Why measure water activity?
Free water in a product influences its microbiological, chemical and enzymatic stability. This is of great importance for perishable products. If there is too much free water, the food can spoil. Too little water can adversely affect product properties. The measurement of water activity also provides useful information about characteristics such as cohesion and storability, along with flow properties of powders and adhesive of coatings.
What is equilibrium relative humidity or ERH?
ERH is the value of relative humidity into which a hygroscopic product can be placed where no net exchange of moisture between the product and surrounding environment can take place. It is expressed on a scale of 0….100%. ERH can be applied to almost any product that is sensitive to moisture, or where the presence of moisture can affect product handling.
Aw or ERH?
Both Aw and ERH are an expression of the amount of free water vapor present on a product, both at its surface and within its structure, and are practically the same measurement expressed in a slightly different way. Reference to water activity can be interchanged with ERH. Examples: 0.1aw = 1%RH and 0.8aw = 80%RH. Rotronic products offer the user the option to select display units as Aw or %RH.
What is water content?
Water content, when referring to a solid material, is an expression of the percentage of the materials weight which is water (both in liquid or gaseous phase); usually referred to as ‘percent moisture content’. This term is widely used in many areas of industry.
Water activity or water content?
Water content is used to control the amount of water present in a product for quantitative reasons. If a product is sold by weight, controlling its water content may be useful in maintaining product quality, but can also impact profitability. Water activity is more significant for qualitative considerations such as product stability, shelf life (e.g. microbiological & enzymatic stability, aroma retention), handling characteristics, physical properties, and chemical stability. The user should decide which parameter of measurement is best suited to their products and processes. For quality control purposes moisture content limits are easily converted to water activity limits by very simple comparative tests. Water activity measurement offers a non-destructive, easy-to-use measurement in a wide range of convenient configurations for both laboratory and on-site production areas.
Source: Rotronic Measurement Solutions