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.

An investigation was undertaken to establish whether lignification was a possible mechanism contributing to the hard‐to‐cook defect in beans (Phaseolus vulgaris). Cell wall material (CWM) from control and defective beans was isolated and microscopic techniques employed to compare the two fractions. Transmission electron microscopy indicated that potassium permanganate‐fixed material had heavier deposition of manganese dioxide in cell corners, secondary walls and middle lamella of hard beans, a pattern seen during the lignification of plant tissue. CWM from hard beans had a lamellated appearance not seen in the control as viewed by scanning electron microscopy. It is suggested that this is a result of cellulose deposition, a process known to occur before lignification. This tentative evidence of lignin within the cell walls of legume seeds has a host of implications for hydration during cooking, cell separation and ultimately, texture.

Water absorption, solids loss, and electrolyte leakage were determined for soft and hard black beans during the soaking and cooking processes. All three parameters increased in hard beans during soaking. It is hypothesized that membrane damage or deterioration is responsible for these differences. During cooking, hard beans lost fewer solids and minerals and did not continue to hydrate to the same degree as the controls, probably as a result of restricted cell separation. Microscopic evidence indicated reduced starch gelatinization in hard beans. This is attributed to reduced water absorption.The hard-to-cook defect that develops in dry beans stored under conditions of high temperature and high humidity has been investigated extensively. One often-

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