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An Industry Breaks Out of its Shell

Diamond Foods is the world’s largest walnut-processing plant, with approximately 50 percent of the California walnut crop passing through the doors of its Stockton plant.

The California walnut industry began when Franciscan fathers brought over the earliest walnuts, known as “mission” nuts. Trees were planted and flourished in the state’s warm, Mediterranean-like climate, and by the 1870s, commercial walnut production began in Santa Barbara.

Southern California was responsible for up to 65 percent of all walnut acreage for nearly 70 years. When areas to the north proved to offer higher yields — due to better growing areas, improved irrigation, and better pest control methods — the center of walnut production shifted northward.

Today, the Central Valley is California’s primary walnut growing region, and the state as a whole is responsible for 99 percent of the commercial U.S. supply and three quarters of world trade of walnuts.

Harvesting in a Nutshell

California produces many varieties of walnuts, though six account for more than 75 percent of total production: Hartley, Chandler, Serr, Vina, Franquette, and Howard. The state boasts more than 4,600 growers, many of which are family farms, such as R&A Miller, which has been in the walnut business for several generations.

Located in Linden, CA, in the San Joaquin Valley, R&A Miller is managed by David Miller, whose great grandfather started the orchard at the turn of the twentieth century. The orchard began with peaches as its primary crop, supplemented by a number of walnut trees.

Miller’s grandfather continued to grow the business and, in the late 1930s, built a walnut huller designed for commercial production, cementing the family’s stake in the industry. Today, Miller runs the mid-sized business alongside his father and brother.

The orchard grows 10 walnut varieties and can process up to 120 tons per day during harvest, which begins in early September and lasts through the first week of November.

Before a walnut orchard can harvest its first crop, it has to go through a development process. Under ideal conditions, walnut trees can grow as high as 100 feet, with roots as deep as 10 feet.

“It takes about three years of raising the trees, and in the fourth year, you’ll start to get a little bit of production,” Miller says. “It takes until about the seventh year to get into full production.”

Walnut harvesting begins when the drying green hulls start to split, allowing the in-shell walnuts to be removed. Orchard workers use a mechanical shaker to vigorously shake the nuts from the trees in blocks of 20 to 30 acres at a time.

Once the nuts are on the ground, orchard workers bring through the sweepers, smaller machines equipped with air blowers that sweep the walnuts into windrows. Then mechanical harvesting equipment is used to pick up the walnuts and places them into trailers.

From there, the nuts are transported to the hulling facility. The outer green husk is removed by a huller, and the walnut is mechanically air dried to an optimum 8 percent moisture level, preventing deterioration of the nut and ensuring quality during storage. Once the walnuts are cleaned and dried, they are packed into trucks and shipped to a nut production plant for further processing.

Though it features a short harvest season, the walnut business is a year-round job, Miller says. “As soon as we’re done with harvest, we start troubleshooting the processing equipment while it’s fresh in our minds. Because it’s only a month-and-a-half-long season, we can’t have any breakdowns because we have to get a year’s worth of production through the plant [in a short amount of time]. We can’t have any failures.”

Cracking the Challenges

Walnut growers are constantly searching for innovative new technologies, as well as ways to reduce costs. “We have to be more efficient with our use of water and energy for cost and safety reasons,” Miller says.

When it comes to food safety, Miller says the industry is thankful to have a naturally clean product, though there are still some challenges. Walnuts are susceptible to various pests, and growers must constantly monitor their orchards for bugs and bacteria that could potentially compromise water or air quality, and contaminate the nuts.

The University of California Agricultural & Natural Resources has developed a year-round integrated pest management (IPM) program to help growers solve pest problems through both chemical and nonchemical procedures, while minimizing risks to the public and the environment.

Walnut quality is also highly dependent on weather conditions. A dry autumn with mild temperatures makes for an ideal harvest. Miller says the last two harvest seasons have been problematic because of too much rain, which can compromise product quality due to mold. Excessive rain can also cause the ground to become too saturated to support heavy harvesting machines.

Despite these challenges, Miller says that, overall, the industry is strong. The 2011 walnut yield was estimated at 485,000 short tons, the second largest crop on record.

The Nuts & Bolts

California is home to more than 70 walnut processors, which ready the product for distribution to retailers, commercial ingredient buyers, and foodservice customers. Diamond Foods is the world’s largest walnut processing plant, with approximately 50 percent of the California walnut crop passing through the doors of its Stockton, CA plant.

Diamond was established in 1956, when it began processing walnuts. The 70-acre facility features 635,000 square feet of office and production space with an additional 120,000 square feet of refrigerated storage space.

Walnuts are the flagship product of the Diamond brand. Diamond sends trucks to its network of 1,700 walnut growers to transport the nuts to the Stockton plant, where they are processed and packaged. Four California receiving facilities in Live Oak, Linden, Modesto, and Visalia assist with collection during the walnut harvest season.

The trucks arrive at the facility where they are weighed at the scale and unloaded. Product samples are taken during the unloading process to determine the quality of the delivery.

To help ensure walnuts meet quality standards, Diamond conducts and sponsors seminars with its growers to promote Good Grower Practices for water reduction, IPM, and yield enhancement. Additional grower services are also provided, including the 24/7 Ranch Pickup program, which utilizes trailers with onboard moisture meters to ensure acceptable moisture levels. Diamond growers also have online access to delivery, grading, and payment information.

Once product quality has been assessed, walnuts destined for shelled products are routed into the plant to be sized and stored. Nuts are sent through a mechanical cracker and vacuum sorter to separate the shell before the nutmeat is sent through a laser sorter to remove any remaining shell or defects.

The plant yields nearly 100 million pounds of walnut shells from each production year. All leftover shells are sold to other industries which use them in a variety of ways, including as a binder in sealants and glues, in sandblasting and cleaning, as a cosmetic ingredient, and for fuel.

Diamond walnuts go through a variety of processes, depending on their intended use. Culinary nuts designed for cooking and baking may be sold whole, sliced, diced, chopped, ground, or in-shell. Diamond’s Emerald snack line includes walnuts for products such as mixed nuts, dry roasted walnuts, glazed walnuts, and a variety of trail mixes.

A Fertile Future

California walnut production has doubled in the last ten years, according to the California Walnut Board and California Walnut Commission. While the U.S. continues to be the industry’s largest market, overseas markets have grown significantly in recent years. In 2010, 61 percent of the walnut crop was exported.

“Much of the increase in demand is driven by promising results from two decades of health research on walnuts in the areas of heart health, cancer, diabetes, cognitive function, and more,” says Jennifer Getz Olmstead, Domestic Marketing Director for the California Walnut Board and California Walnut Commission.

California walnuts were recently certified as a heart-healthy food by the American Heart Association and can now carry the Heart-Check mark on packaging. “This is great news, as the Heart-Check mark is the most widely recognized mark in grocery stores,” Olmstead says.

As the industry continues to grow, walnut growers and processors look forward to a fertile future supported by the strength of a naturally healthy product. “We are fortunate to have a product that has a great health message,” Miller says. “It’s a simple food that carries many health benefits, which helps both our industry and the consumer.”