Introduction Water activity (a w ) refers to the vapor pressure of a liquid divided by the vapor pressure of pure water at a consistent temperature (Berry, 1990). It is a concept used to define the relationship between water and certain compounds (Slade and Harry, 1991). Berry (1991) defines water activity as the amount of water needed to support the growth of microbes. Microbes are organisms that include yeast, mold and bacteria (Sloan, 1977). It is measured on a scale of 0 to 1.0 (Slade et al. 1991). Berry (1990) asserts that the water activity of baked goods can be calculated by establishing the weight of the food in relation to its dry mass. The difference between these values represents the product’s moisture content (Berry, 1990). “As the relative amount of solutes in the water increases – by direct addition and/or a drying process – the water which is free and available to microorganisms decreases. Some examples: Foods A and B may contain the same high amount of water but differ significantly in the amount of NaCl. Foods C and D may have the same amount of NaCl but different amounts of water. As NaCl in food is always dissolved in the water (up to the saturation point), the concept of available water (a w ) becomes more important than simply the amount of water in a food” (Lindquist, 1998). Water activity is directly proportional to temperature as long as several factors remain constant (Sloan, 1977). Crystalline substances like sugar and sodium carbonate are known to slow down the rate of water activity. Bakeries use water activity to determine the shelf life of certain products. Water activity can help bakers determine the best ingredients to use in food production. This knowledge can be used to inhibit the growth of mold in products that are made using dough (Slade et al., 1991). It can also be used to reduce the rate of moisture migration in certain products (Berry, 1990). Bakeries use water activity as a critical control point with regard to Hazard Analysis Critical Control Points (Slade et al., 1991). This process involves the periodic sampling of products, which are tested to determine their different rates of water activity (Berry, 1990). It is used to determine the appropriate water activity rates for certain pastries. These rates can be used to establish the expiration date of certain pastries. Water activity is often responsible for bacterial growth (Berry 1990). Bacterial growth can also be inhibited based on the particular rates of water activity (Slade et al., 1991). Reducing the water activity in dough causes bacterial growth levels to fall (Sloan, 1977). Measuring Water Activity The values of water activity can be determined through the use of capacitance hygrometers and dew point hygrometers (Berry, 1990). A capacitance hygrometer is an instrument that consists of a membrane that is placed between two charged plates (Slade et al., 1991). The device determines the equilibrium of vapor in a chamber which houses the sample (Berry, 1990). Hazards Controlled by Water Activity When certain baked goods are kept under certain conditions, they experience a progressive deterioration of quality (Slade et al., 1991). These changes are determined by the content