Evaluation of a model of organic acid flavor thresholds in beer

A formula that successfully models the flavor thresholds in beer of organic acids as a function of their molecular properties (R-2 = 0.905) was previo usly developed. The predictive ability of the model was evaluated by intern al and external validation. Cross-validation of the original data set produ ced an R-2 of 0.842, which represents a more conservative estimate of the m odel's predictive ability. Flavor threshold determinations were attempted w ith four acids whose thresholds in beer were not available in the literatur e. In three of the four cases (benzoic, fumaric, and sorbic acids), the sol ubility limit of the acid in beer was exceeded before the threshold was enc ountered. The observed threshold for heptanoic acid (2.3 mglL) was reasonab ly close to the model prediction (18 mg/L). The model was also used to make predictions for acids other than those used to construct the model. The tw o acids that had structures similar to those in the original data set, isob utyric and isovaleric, showed reasonably close agreement between observatio n and prediction. For two acids unlike any in the original data set, phenyl acetic and gallic, predictions were wildly inaccurate.