Pinto Bean Storage to Maintain Quality
April 15, 2002
Kenneth Hellevang, Agricultural & Biosystems, Engineering Department, North Dakota State University
Pinto beans were obtained from a farmer at about 20% moisture and dried to the desired moisture contents of 14%, 16% and 18% wet basis. The beans were stored in covered 5 gallon pails for 10 months at 20°F, 40°F, 60°F and 80°F.
The change in color quality was measured with a Hunter colorimeter. The Hunter-L (lightness or whiteness) values for the beans stored at the specified temperatures and moisture contents are shown in Table 1. There was a dramatic decrease in the lightness or whiteness of the beans stored at the warmer treatments. The beans stored at 20°F and at 40°F had very little if any change in lightness for all three moisture contents. The beans stored at 80°F and 18% moisture had considerable mold growth on the beans at the end of the storage period.
The Hunter-a values (redness) for the beans stored at the specified temperatures and moisture contents are shown in Table 2. The beans stored at 20°F and at 40°F had very little if any change in redness for all three moisture contents. Beans stored at the warmer temperatures increased in redness.
The pinto beans were checked for the hard-to-cook characteristic after ten months of storage, Table 3. Shorter cooking times are desired. The average cooking time prior to storage was 18.4 minutes. There was a dramatic difference in cooking times for the various treatments. After 10 months of storage, cooking times of 16% and 18% moisture beans stored at 20ºF were only 1.2 times longer than before storage and at 40ºF were only 1.7 times longer. The beans stored at 60ºF had cooking times about twice as long as before storage. The beans that were stored at 80°F had cooking times that were 3.6 to 9.2 times longer than prior to storage.
Beans at 16% moisture content, in a box maintained at 80°F, were exposed to a grow light bulb representing the light spectrum of the sun to determine the affect of light on bean color. The beans darkened dramatically within weeks. The Hunter L-value decreased from 52.4 to 44.9 during three months of storage. The color darkened more quickly at the beginning of the storage period, with 77% of the darkening occurring during the first 5 weeks. The Hunter-a values increased from 5.2 to 8.1 indicating an increase in the redness of the beans, which is also deterioration in color quality. The Hunter-b value decreased from 12.5 to 10.6 indicating a decrease in the yellowness of the beans.
The measurement of the resistance to airflow of pinto and navy beans found the resistance to be similar to that of soybeans.