[Evaluation of a device to measure the hardness of the bean grain (Phaseolus vulgaris) and its use in the determination of cooking time].

A simple equipment named DUR-INCAP was developed to study the factors responsible for the hard-to-cook beans and for other purposes related to this problem. The instrument measures objectively the hardness of individual beans, expressing the result as gram-force. The document describes the equipment. As a first step in establishing the usefulness of the equipment, a study using four white, four black and four red-colored beans, purchased in the market, was undertaken. Likewise, a black bean (Tamazulapa) harvested in January, 1983, and stored for one year at 5 degrees and 25 degrees C, and the same cultivar harvested in January, 1984, were also used. All beans were cooked in boiling water (95 degrees C) at atmospheric pressure for 30, 60, 100, 140 and 180 min. At each cooking time, a sample was withdrawn and its hardness measured individually on 25 kernels, with the DUR-INCAP. With the help of experienced persons in cooking, the hardness at each cooking time was classified into soft cooked beans (less than 100 g-force), medium (between 100-200 g-force) and hard (above 200 g-force). Results were as follows: white and black beans reached softness at 140 min of cooking, with the exception of one black sample which required 180 min. Two of the four red beans required 180 min, and the other two, needed 40 additional min. The effects of storage time and temperature on hardness became evident in the study with the black bean Tamazulapa. The sample stored for one year at 25 degrees C needed 140 min cooking time, while the sample stored at 5 degrees C and the one harvested in January, 1984, required 100 min. These initial results suggest that the DUR-INCAP instrument may be useful for the study of the hard-to-cook bean problem; however, additional analyses are required.