Karmas and Chen have shown a correlation between water activity and water binding in high- and intermediate-moisture food systems. In their study of carboxymethylcellulose, casein, oil, water, and glycerol, they found a significant effect on water binding, yet none on water activity. They also determined carboxymethylcelluose to be a better water binder than casein, with glycerol lowering water binding. (Karmas, E., Chen, C. Relationship between water activity and water binding in high and intermediate moisture foods. Journal of Food Science ,40: 800-801, 1975.)

Foods are categorized as to their water content:

low moisture ~0-12%

medium moisture ~15-60%

high moisture ~60-99+%

Karmas and Chen frequently discuss the "isotherms" of a food item. An isotherm describes the equilibriun relationship between water adsorption by the food components and vapor pressure.