Food Engineering

Optimizing walnut moisture content is a win-win-win

June 1, 2011
(Clockwise, starting at top left): Walnuts arrive in trucks; walnuts are then placed in drying bins; Opto 22 SNAP PAC brains and I/O bring in sensor data and control drying systems (fans and burners); HMI screen from WECO allows operators to adjust critical set points, maximizing product quality and energy usage.


Fedora Farms, located in Meridian, CA, is one of the largest walnut processing facilities in the country and has succeeded in cutting its operating costs by implementing energy-efficient processing equipment. This family-run business has always put quality first and uses automation technology in several phases of walnut processing, including hulling, conveying and, perhaps most importantly, drying the walnuts and monitoring their moisture content.

After the walnuts are shaken from the trees, they’re gathered and brought into the Fedora facility so processing can begin immediately. The nuts’ outer coverings are hulled, and the walnuts are then dried to 8 percent moisture content.

“Quality is most important,” says Fedora Farms’ Chris Fedora. “We want to ensure that we deliver nice, healthy meat kernels at maximum weight so we can get the highest return. We also want to free up the dryers as quickly as possible so we process product faster.”

Fedora enlisted the expertise of Woodside Electronics Corporation (WECO)-specialists in sorting and automation solutions for the agricultural industry-to implement the necessary monitoring and control hardware.

“Although we’re always in a rush during harvest, we only dry walnuts at a maximum temperature of 110°F,” says WECO’s Don Osias. “Any higher temperature would reduce the quality and character of the walnut’s healthy oils.”

The goal is to dry the nuts to about 8 percent moisture. Over-drying can be detrimental in several ways. In addition to the cost of the unnecessary fuel and power used to run the dryer, over-dried nuts become brittle and are easily broken during handling. Additionally, if the nuts stay in the bins too long, the processing of the total crop slows, and the nuts lose moisture content and weight, which means less profit for the grower.

WECO provided Fedora Farms with custom-designed, portable moisture meters and automation hardware that provide moisture information and control the dryers’ fans and burners. Opto 22 SNAP PAC brains (processors) and I/O are the key components used in WECO’s automation systems. Analog and digital input modules gather all process data and adjust temperatures and other variables. Analog and digital output modules control the air doors, fans and burners. Networked scanners collect the moisture information from each bin and send it to a PC in either text or graphics so operators know exactly how the drying process is progressing.

Fedora’s automation system uses the moisture information to open and close the air door under every bin at just the right time, and start and stop the drying process. Fans and burners are shut down as soon as the nuts in the bins are dry. This makes processing faster, increases profit and saves energy.

“Monitoring the moisture in those bins and having the automated door controls allows us to hit that 8 percent, shut things off and ship the product right away, which frees up more dryer space,” says Fedora.

View a video of this story at the Opto 22 web site.

For more information, James Davis, 951-764-4748, jdavis@opto22.com