Microwave meter boosts peanut testing

By Rory Harrington

- Last updated on GMT

Related tags Moisture content Radio

Quicker and easier analysis of the moisture content and density of in-shell peanuts are benefits claimed for a new microwave meter developed by the US Department of Agriculture (USDA).

The new equipment will “instantaneously”​ determine these “important quality indicators”​ for peanut processors and producers, said the USDA’s Agricultural Research Service (ARS). The microwave meter also measures density and moisture independently, which cuts out the need for an extra testing step. The apparatus is an enhancement of previous technology from the unit that used radio frequencies to gauge moisture content.


The moisture content of peanut kernels, which must be less than 10.5 per cent, is the most important factor in determining quality. Moisture levels topping this can lead to the growth of fungi that produce aflatoxins, said an ARS statement.

The new equipment means peanut graders can find peanut kernel moisture content with a standard error of around 0.5 per cent.

“The method is rapid, nondestructive and eliminates the need for shelling the peanut pods”, ​said Samir Trabelsi and Stuart O. Nelson, who developed the kit at the ARS’s headquarters in Athens, Georgia.


The new process sees in-shell peanuts loaded directly into the microwave meter’s sample holder, after which an antenna transmits low-intensity microwaves into the pods.

The microwaves, which travel through the nuts, are received by a second antenna directly opposite. The pod’s moisture content and bulk density are revealed by a computer that measures alterations in the energy level and speed of the waves as they pass through the peanuts. For moisture content, the new technique also eliminates the need for multiple calibrations and compensates for density and temperature, said the ARS.

The meter has been granted a provisional patent and is currently being tested at five peanut stations in the US southern states.

The quality of processed peanuts made national headlines in the US after contaminated nuts from the Peanut Corporation of America were linked to eight deaths and hundreds of illnesses nationwide.

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