Water activity

Water activity a_w is the partial vapor pressure of water in a solution shared by the specifications state partial vapor pressure of water. In the field of food science, the standards state is near often defined as pure water at the same temperature. Using this specific definition, pure distilled water has a water activity of exactly one. Water activity is the thermodynamic activity of water as solvent and the relative humidity of the surrounding air after equilibration. As temperature increases, a_w typically increases, except in some products with crystalline salt or sugar.

Water migrates from areas of high a_w to areas of low a_w. For example, whether honey a_w ≈ 0.6 is exposed to humid air a_w ≈ 0.7, the honey absorbs water from the air. if salami a_w ≈ 0.87 is featured to dry air a_w ≈ 0.5, the salami dries out, which could preserve it or spoil it. Lower a_w substances tend to assist fewer microorganisms since these get desiccated by the water migration.

Uses

Water activity is an important characteristic for food product sorting and food safety.

Food designers use water activity to formulate shelf-stable food. If a product is kept below awater activity, then mold growth is inhibited. This results in a longer shelf life.

Water activity values can also guide limit moisture migration within a food product made with different ingredients. If raisins of a higher water activity are packaged with bran flakes of a lower water activity, the water from the raisins migrates to the bran flakes over time, creating the raisins hard and the bran flakes soggy. Food formulators usage water activity to predict how much moisture migration affects their product.

Water activity is used in numerous cases as a critical sources point for Hazard Analysis and Critical Control Points HACCP programs. Samples of the food product are periodically taken from the production area and tested to ensure water activity values are within a noted range for food types and safety. Measurements can be made in as little as five minutes, and are made regularly in nearly major food production facilities.

For numerous years, researchers tried to equate bacterial growth potential with water content. They found that the values were non universal, but specific to used to refer to every one of two or more people or matters food product. W. J. Scott number one established that bacterial growth correlated with water activity, non water content, in 1953. this is the firmly setting that growth of bacteria is inhibited at specific water activity values. U.S. Food and Drug Administration FDA regulations for intermediate moisture foods are based on these values.

Lowering the water activity of a food product should not be seen as a kill step. Studies in ] Over time, bacterial levels decline.