New Walnut Drying Technology Helps to Make the (Harvest) Season Bright

Imagine chestnuts roasting on an open fire. Now substitute walnuts for chestnuts. Now substitute infrared technology for the open fire. It may not invoke warm and nostalgic feelings like the famous Christmas song, but to walnut growers in the state, a new high-tech drying system funded in part through the California Energy Commission, could be one of the best presents they could ever ask for.

Top Image: UC Davis professor Dr. Zhongli Pan (top right) and researcher Chandraseker Venkitasamy (bottom left) discuss the walnut drying process with Energy Commission specialist Leah Mohney (right).

Bottom Image: A technician uses a scanner to monitor temperatures as walnuts go through the drying process.

Recently, UC Davis, with help from a $1.1 million Public Interest Energy Research Program (PIER) grant, began demonstrating a new commercial walnut drying system that could save growers as much as 50 percent in energy costs.

Walnuts are big business in California with the state producing almost all of the walnuts in the country – about 570,000 tons last year according to the U.S. Department of Agriculture (USDA). But, walnut production is expensive and energy intensive. It takes about 12 therms of gas and 24-kilowatt hours of electricity to dry one ton of nuts using standard processes, according to researchers at UC Davis.

Nuts must meet strict USDA standards for moisture content. With traditional methods, they are washed then moved to large drying bins where hot air is circulated for 12 to 24 hours. It’s an inexact science since nuts differ in size, have differing moisture levels and are located at different depths within the bins. Some are dried too much and become brittle, and some are not dried enough making them susceptible to mold.

The infrared process is more energy efficient because it quickly removes most of the surface and shell moisture from walnuts before they are sent to the bins. Hot air is still required for the final drying process but it is needed for a much shorter time period. Tests so far show that walnuts dried through the infrared process have a more uniform moisture content. Tests also show a decrease in product loss.

The demonstration runs through March 2018, and if it continues to be a success, who knows, walnuts desiccating on an open infrared dryer could become a hit after all.