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The Case for Water Activity as a Specification for Wheat Tempering and Flour Production

Carter, B. P., Galloway, M. T., Morris, C. F., Weaver, G. L., Carter, A. H.
Cereal Foods World 2015 v.60 no.4 pp. 166-170
flour, grain foods, microbial growth, molds (fungi), sorption, tempering, testa, water activity, water content, wheat
Moisture plays an important role in processing wheat grain into flour, from proper grain tempering to the stability of the flour. Moisture properties of dry grain, tempered grain, and finished flour are currently tracked using moisture content. However, stability factors such as microbial growth and chemical stability are better correlated to water activity rather than moisture content. To determine if water activity could be utilized as a more effective specification for flour production, the water activity and moisture sorption properties of dry grain, tempered grain, farina, and flour were determined. The water activity of dry grain was found to be sufficiently low enough for long term stability. Dynamic isotherms of dry grain indicated a critical water activity where the seed coat lost its resistance to water penetration, which corresponded with the water activity of tempered wheat. Finally, the water activity of finished flour and farina was found to typically be below the critical water activity for mold growth. Based on the results of the study, it appears that all current recommended moisture levels for grain were established unknowingly based on water activity. Consequently, it would be more effective to set specifications for grain handling and processing based on water activity rather than moisture content.