Multiple mechanisms of bean hardening

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Abstract
Several aspects of the hard‐to‐cook phenomenon in black beans were investigated. Bean hardening had commenced by the fourth month of storage at 30°C and 85% RH. The heat treatment used in this study caused initial softening but actually potentiated the defect once the beans were subjected to high temperature and high humidity. Both hydration and soaked hardness analyses indicated that the small differences in water absorption between hard and soft beans could not account for the large differences in cooked hardness. Increased hardness of raw defective beans was not related to cooked hardness but to elevated moisture levels. A multiple mechanism for bean hardening is presented which includes phytate loss as a minimal contributor to cooked hardness during initial storage and phenol metabolism as a major contributor on extended storage. The phenol metabolism is thought to be a lignification‐like mechanism.