Process and Operations / Heating: Cookers, Dryers, and Ovens

Dehydration: Which Option is Best for Your Food Processing Plant?

Food manufacturers can choose from a number of developments that optimize moisture removal and minimize process cost.

By Kevin T. Higgins, Managing Editor

Moisture removal is a fundamental process in food production, arguably second only to cooking for stabilization and preservation for both solid and, in the case of milk powder, fluid foods.

How much water is removed and the impact on what’s left behind is the job of dryers, and food processors have multiple options to attain a desired outcome. While it’s often an essential step, drying can be energy intensive and destructive of a product’s appearance and nutritional value. Stabilization at minimal cost is an ongoing R&D focus, and considerable progress is being made.

Drying with microwave energy under vacuum was first applied commercially in the 1980s. Every technical innovation experiences growing pains, and the higher cost of electricity compared to natural gas works against microwave drying. But low-pressure microwave stacks up well against freeze drying’s energy profile, and a variation called radiant energy vacuum (REV), first applied in 2008, is starting to gain industrial traction.

In August, Jack Link’s Beef Jerky became the latest food processor to sign a licensing deal with EnWave Corp., Vancouver, British Columbia. to evaluate the technology. The Minong, Wis., meat firm declined to discuss what value drying would add to products that already are shelf stable, referring instead to interest in “a variety of innovative snack products.” But two start-up companies with financial ties to EnWave are pressing ahead with shelf-stable cheese snacks that are enjoying early success at Costco, Kroger and other retailers.

Hydroelectric is a big part of the energy portfolio in the Pacific Northwest, and that helps EnWave stake a low-carbon footprint claim, at least when its machines are operating on its home turf. The vacuum level cuts the boiling point in half, and microwave energy removes moisture without collapsing the food’s cell structure.

Freeze drying also uses vacuum, but the process is longer and consumes more energy because of the multiple phase changes the food undergoes, according to Brent Charleton, EnWave vice president. REV accomplishes similar quality outcomes to freeze drying in a shorter time and at a cost closer to convective air drying. Product is loaded into carriers that tumble through the dryer, mimicking the effect that a turntable has in a home microwave oven.

NutraDried LLP, a Ferndale, Wash., processor formed last year and jointly owned by EnWave and a capital investment group controlled by an EnWave director, recently started producing Moon Cheese on a 100 kW machine, replacing a 10 kW system similar to the units used by Jack Link's and others.

“The 10 kW machine was more or less a pilot line for us until we got into about a hundred stores and could justify the bigger machine,” explains Alan Whittecker, CEO of NutraDried. The bigger unit outputs about 450 lbs. of low-moisture (typically less than 1 percent) of fresh cheese that’s shelf stable for 12 months, delivering “the fantastic taste of cheese” without preservatives or other additives, he adds. The company started shipping product from the larger dryer Dec. 2.

Air replaces moisture in the cheese as it evaporates, causing the product to puff up and resemble lunar rocks, according to Whittecker, explaining the inspiration for the product’s name. “It has a really nice crunch, unlike the spongy, almost Styrofoam mouthfeel of freeze-dried cheese,” he says.

Baking can produce shelf-stable cheese, “but with not nearly the flavor delivery and nutritiousness.” Outdoor enthusiasts are among the consumer segments targeted with the cheddar, gouda and pepperjack varieties, which typically retail at $4.99 for a 2-oz. package.

“It’s a relatively expensive snack,” concedes John Gibb, CEO of NutraDried Creations, a Blaine, Wash., copacker created to market private-label fresh cheese produced in bulk in Ferndale and packaged in Blaine. Gibb’s firm created Munchies for sale in Costco stores in the Northwest. Based on positive sales results, he expects a Kirkland version of the cheese snacks to debut in 2015.

Streamlined engineering

Sanitary design of equipment is front and center for both processors and OEMs, but considerable confusion exists, particularly when the application involves low-moisture foods. Requests for quotes often compound the problem, with food companies mixing and matching from guidelines that may or may not be appropriate for the application. The result is added cost for over-engineered equipment.

The One Voice initiative by the Alliance for Innovation and Operational Excellence is designed to address the understanding gap and move OEMs toward greater standardization that lowers equipment costs. Industrial dryers recently were addressed by One Voice’s engineering and solutions group, and the exercise helped guide development of a hygienic dryer for ready-to-eat cereals coated with sugar and other flavors.

“We were doing the development of the Ceres dryer while I was involved in the One Voice group developing the dryer guidelines,” recalls Steve Blackowiak, food safety manager at Buhler Aeroglide, Cary, N.C.

The distinct requirements for high vs. regular hygiene and wet vs. dry applications had a direct impact on the detailed engineering work for the firm’s Ceres cereal dryer. It also provided insight into how food companies view low-moisture products, which is altering Aeroglide’s approach to some customized solutions. For example, two projects, one involving pelletized baby food, the other dry pet food, fall into the high hygiene, dry cleaning quadrant, so the same sanitary design principles will be applied to both.

There’s no shortage of sanitary guidelines for food processing equipment — AMI for meat and poultry, 3A for dairy, BISQ for bakery, etc. — and that creates confusion for OEMs and a mix-and-match approach by individual food companies. “You can’t apply 3A specs to low-moisture drying equipment because it would then be overdesigned and very expensive,” Blackowiak points out.

By bringing major purchasers such as ConAgra, Kellogg and MOM Brands (formerly Malt-O-Meal) together to develop consistent guidelines, Buhler Aeroglide was able to design five standard dryer models, including the cereal dryer that will require modest modifications for individual purchasers.

Food safety, maximum production and energy efficiency drove Ceres’ design. Direct-drive fans replace the belts and pulleys in earlier dryers, a change that addresses all three goals by making it easier to clean the more efficient fans and helping shrink cleaning cycles. Cereal makers reported spending 8-14 hours on dryer cleaning. Ceres can be cleaned in two hours, giving users 6-12 additional hours of uptime.

The single-plenum design delivers significantly greater air velocity, which allowed engineers to shrink the machine’s footprint by about a fifth while delivering comparable throughput of about 8,800 lbs. per hour. Chainless conveyors, elimination of side rails and greater use of CIP (some manual cleaning still is required) are among other improvements.

A better understanding of material science is leading to game-changing refinements in dryers. A recent example is the Ecothermatik dryer for long-goods pasta from Blackowiak’s Swiss colleagues at Buhler AG. Scientists began by studying the starch-protein structures within the dough so they could better control glass transition, the point at which a rubbery consistency becomes hard and brittle. The result is a dryer that consumes 40 percent less thermal energy and 10 percent less electrical energy than Buhler’s previous model.

The dryer, which will share the spotlight March 24 at a resource efficiency conference held in conjunction with Anuga FoodTec trade show in Cologne, Germany, was honored with an International FoodTec Award in 2012, the last time the triennial show was staged. The award “recognizes innovations that assist food manufacturers with improving their processes,” according to Matthias Schlueter, the show’s project manager (www.anugafoodtec.com).

Benchmarking against its high-volume conventional dryer with a capacity of 2,750 lbs. per hour, Buhler engineers calculated the new system reduced overall operating costs about 30 percent. Instead of simply exhausting humid air from the pre-dryer and main dryer, the air is routed through heat exchangers to recirculate the heat. Because the pasta stabilizes more quickly, total drying time is reduced 20-25 percent, and the dryer’s footprint is reduced.

Fresh powder

Spray dryers are among the biggest energy consumers in the food industry. Officials at GEA Process Engineering believe the spray dryer that began producing milk powder in 2013 at Fonterra Co-operative Group’s plant in Darfield, New Zealand, is the world’s largest. The unit produces 30 metric tons (66,000 lbs.) of powder an hour.

A twin to this tower of drying power will go into production this year. While declining to comment specifically on the Fonterra units, officials at GEA in Soeburg, Denmark, (www.gea.com) note that the use of computational fluid dynamics (CFD) for chamber sizing and advanced understanding of glass transition have contributed to reductions of 5-10 percent in energy consumption of large-scale spray dryers in the last few years.

“Over the past 10 years, the performance of powder production has improved strongly, primarily by focusing on fewer products per dryer and (producing) products for a long time without interruptions, using 24/7 operation capability,” writes Thorvald Ullum, vice president-technology in an e-mail response. “In that way, a minimum amount of out-of-spec product is made during start and stop or during product changeover.

CFD helped GEA optimize the size and shape of drying chambers, reducing the amount of air needed. Reuse of the evaporator’s cooling water to preheat the main dryer’s air further reduces energy use. “Up time is today very high, especially for plants with a structured approach to plant maintenance,” he adds, with some dryer operations operating “very close to an OEE of 100 percent.”

Most equipment improvements yield only incremental improvements, but by applying design tools like CFD to a better understanding of phase changes in the food itself, dryer builders are realizing significant advances in performance and energy consumption.