Seed researchers often focus on improving certain aspects of a product, whether through breeding, transgenic manipulation or by protecting the quality of a seed that will be planted. When the seed is also the edible product, research often takes a different course. Almonds are edible seeds that have been under scrutiny in the past few years. Two outbreaks of salmonella spurred legislation mandating the chemical or steam-based pasteurization of all California almonds. Colony collapse disorder threatened California’s almond growers as well as apiaries and honey producers nationwide. A third issue has been a concern since humans began cultivating almonds and other seeds: moisture content.


All biological materials are made of water, including grains and seeds. Moisture content is a key parameter in determining the harvest time, as well as the optimum condition for transportation, storage and processing of almonds. Optimum moisture content for storage and processing of almonds is less than 6 percent. Almonds with a water content of greater than 7 percent risk growth of aspergillus mold, which produces aflatoxin, a suspected carcinogen known to cause severe liver damage.

Typically, growers and processors have relied on sun-drying, electric dehydrators, and oven-drying techniques combined with electrical and electronic-type moisture meters. Yet something was missing: speed.

The Almond Board of California identified (and shared with the USDA) a critical need for developing rapid and nondestructive methods and sensors to determine moisture in almonds while still in the field. Dr. Samir Trabelsi, a research electronics engineer with the Quality and Safety Assessment Research Unit at USDA’s Agricultural Research Service in Athens, Ga., was called in. The fact that Trabelsi operates 3,000 miles away from the product is of no concern. For many years, Trabelsi has been involved in research on grain and seed crops that are not grown in Georgia.

In 2009, the electronics engineer began his research. In 2011, he released his findings: that it is possible to determine moisture in both almond kernels and in-hull almonds without touching the almonds. Trabelsi devised a method for accomplishing that.

Trabelsi’s method utilizes low-intensity microwaves to measure the degree of polarization of water in almond samples. Essentially, Trabelsi observes the changes a radio frequency wave undergoes when passing through a container filled with almonds. Water molecules within the almonds act like electric poles on opposite ends of an object (aka dipoles). In the presence of an electric field, the dipoles try to align themselves with the electric field. As this happens, the radio frequency wave changes speed and loses energy. Trabelsi measures these changes and correlates them to moisture content. “The process is very simple,” he explains. “Fill the container with almonds and place them between two antennas facing each other. One is a transmitting antenna and the other is a receiving antenna.”

Because the method is instantaneous, nondestructive, and does not require any physical contact with the material, almond kernel moisture content can be determined while still in the hull. This means that the meter can eventually be made portable for use in the field.

With partial funding from the Almond Board of California, Trabelsi completed the first phase of his investigation in May 2011. However, his work is not complete. Trabelsi has yet to develop a prototype moisture meter. After that, researchers will need to calibrate the moisture meter and test it in the field.

How quickly this happens depends on how much funding is allocated to perform the research and who will pick up the technology to commercialize it. Trabelsi believes his research will benefit commercial almond growers by assisting them in determining the optimum time for harvest, drying and processing of almonds. He says, “It will result in significant savings in time and labor, plus a better way for quality assessment.”

The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.