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Pinto Bean Storage To Maintain Quality
The 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 degrees F, 40 degrees F, 60 degrees F and 80 degrees 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.
Table
1. Hunter-L values (whiteness) for specified storage conditions of temperature
and moisture content during the second year.
|
Date |
Time |
20 degrees
F |
40
degrees F |
60
degrees F |
80 degrees F |
||||||||
|
|
Weeks |
14% |
16% |
18% |
14% |
16% |
18% |
14% |
16% |
18% |
14% |
16% |
18% |
|
10/11/00 |
0 |
52.5 |
52.4 |
51.6 |
52.5 |
52.4 |
51.6 |
52.5 |
52.4 |
51.6 |
52.5 |
52.4 |
51.6 |
|
7/31/01 |
41 |
50.9 |
51.6 |
51.1 |
51.2 |
51.0 |
50.4 |
48.6 |
47.5 |
46.7 |
43.6 |
42.1 |
40.8 |
|
Change |
|
-1.6 |
-0.8 |
-0.5 |
-1.3 |
-1.4 |
-1.5 |
-3.9 |
-4.9 |
-4.9 |
-8.9 |
-10.3 |
-10.8 |
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
degrees F
and at 40 degrees
F
had very little if any change in redness for all three moisture contents.
Beans stored at the warmer temperatures increased in redness.
Table 2.
Hunter-a values (redness) for specified storage conditions of temperature and
moisture content during the second storage year.
|
Date |
Time |
20
degrees F |
40
degrees F |
60
degrees F |
80
degrees F |
||||||||
|
|
Weeks |
14% |
16% |
18% |
14% |
16% |
18% |
14% |
16% |
18% |
14% |
16% |
18% |
|
10/11/00 |
0 |
5.0 |
5.2 |
5.2 |
5.0 |
5.2 |
5.2 |
5.0 |
5.2 |
5.2 |
5.0 |
5.2 |
5.2 |
|
7/31/01 |
41 |
5.1 |
5.3 |
5.4 |
5.5 |
5.7 |
5.9 |
6.6 |
6.9 |
7.1 |
8.9 |
9.9 |
9.6 |
|
Change |
|
0.1 |
0.1 |
0.2 |
0.5 |
0.4 |
0.7 |
1.6 |
1.7 |
1.9 |
3.9 |
4.7 |
4.4 |
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 20
degrees F
were only 1.2 times longer than before storage and at 40 degrees F were only 1.7 times longer.
The beans stored at 60 degrees F
had cooking times about twice as long as before storage. The beans that were
stored at 80
degrees F
had cooking times that were 3.6 to 9.2 times longer than prior to storage.
Table
3. Median pin cooking times for beans stored for 10 months at specified moisture
contents and temperatures. Median
cooking time before storage was 18.4 minutes.
|
Storage
Temperature |
Bean
Moisture Content |
||
|
14% |
16% |
18% |
|
|
Pin
Cooking Time (minutes) |
|||
|
20
degrees
F
|
29.6 |
22.6 |
22.8 |
|
40
degrees
F
|
36.0 |
29.7 |
30.6 |
|
60
degrees
F
|
36.0 |
32.7 |
38.0 |
|
80
degrees
F
|
66.2 |
93.0 |
168.5 |
Beans at 16% moisture content, in a box maintained at 80 degrees
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.
Kenneth
Hellevang
Agricultural &
Biosystems Engineering Department
North Dakota State University
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