Measure peanut moisture while still in shell.

Making sure that peanuts are of the highest quality requires drying them enough to prevent the growth of fungi that can seriously decrease their market value. Now, USDA-ARS scientists have developed a way to determine moisture levels without destroying the peanuts' shells, or pods, as is currently done.

Market value is directly tied to peanut quality, and one of the most important quality factors is moisture content. Peanuts must be dried, or cured, to ensure their moisture content does not exceed 10.5%. This preserves the quality of the product and prevents the growth of microbes naturally present in farm fields. One of these, the fungus Aspergillus flavus, can produce potentially dangerous aflatoxin.

Moisture content in peanuts is presently determined using capacitance-type meters. But it is necessary to shell and clean the peanut samples before they are placed in the sample holder of these meters for measurement. The cleaning and shelling involve a considerable amount of time and labor. Once shelled and cleaned, the samples are usually discarded after measurement. Large quantities of edible peanuts are lost during these tests. It would be useful if moisture content could be determined by making physical measurements on the in-shell peanut itself.

ARS engineers have pursued an alternative to opening pods for testing. Instead, they place intact peanut pods between two plates of an impedance analyzer and use radio frequency to determine the pods' moisture content. U.S. producers have systems in place to reduce moisture content, but the trick is to make sure optimal levels are reached throughout an entire batch of drying pods.

In the Southeast United States, freshly dug peanuts, which contain up to 40% moisture, are allowed to dry on the vine until they reach an average moisture value of about 20%, when they are harvested. Soon after, they're mechanically dried until they have less than 10.5% moisture content to meet grading standards and allow for safe storage. During the drying process, processors must measure moisture content so that they do not dry the peanuts too much, which increases costs and lowers peanut quality. The impedance analyzer is better than current techniques because it is a nondestructive technique.

Further information. Chari Kandala, USDA-ARS National Peanut Research Lab, 1011 Forrester Dr. SE, Dawson, GA 39842; phone: 229-995-7452; fax: 229-995-7416; email: chari.kandala@ars.usda.gov.