Most foods contain sufficient nutrients to support microbial growth.
Several factors encourage, prevent, or limit the growth of microorganisms in foods, the most important are a w , pH, and temperature. Water molecules are loosely oriented in pure liquid water and can easily rearrange. The microbial cell must compete with solute molecules for free water molecules. Except for Staphylococcus aureus , bacteria are rather poor competitors, whereas molds are excellent competitors. A solution of pure water has an a w of 1.00.