Food Engineering

Engineering a "fish-dry"

March 22, 2003
New world technology brings old-world practice into the 21st Century

For centuries, the art of drying fish hadn't changed much on the famed Gaspe Coast in Quebec, Canada, where a handful of fisheries dried their world-renowned North Atlantic cod by sunlight. But that was before a consulting engineer customized existing HVAC technology to improve the productivity, shipment, scheduling and taste of the cod.

Instead of depending on the unpredictable outdoor drying process, which requires at least a week of steady sunshine, fish processor Lelievre, Lelievre and Lemoignan (LLL), Sainte-Therese de Gaspe, Quebec, now uses two custom-manufactured DF-60 Dry-O-Tron dehumidifiers by manufacturer Dectron Internationale of Roswell, Ga. The dehumidifiers supply dry air to racks of fresh cod for 32 to 36 hours in dual custom-fabricated sheet metal drying tunnels inside LLL's 100,000-sq.-ft. headquarters. The air distribution design, 6-ft. by 6-ft. by 40-ft.-long tunnels and equipment specifications were handled by mechanical designer Le Groupe Prodapec Inc., a St. Jerome, Quebec-based consultant specializing in turn-key dehumidification and drying projects.

"We're fulfilling orders more accurately than ever because we can now depend on the product drying and being ready on a predetermined date," said LLL president Rock Lelievre.

In addition to improving product quality, the new high-tech drying process cut labor costs associated with outdoor drying by up to 80 percent. The former drying process required covering the fish every night. Additional labor was required during rainy periods in order to protect the fish from the inclement weather. Flash rains could reduce hundreds of pounds of fish from a potential Class A to Class C product rating, resulting in a 20 to 40 percent reduction in profit margins.

An alternative to outdoor drying is a standard furnace and tunnel arrangement. However, furnaces are inefficient for fish drying because of the large amount of exhaust air that's required. When the airflow absorbs moisture from the fish, half of the return air must be exhausted while the remaining half is mixed with dry outside air that requires additional heating.

For LLL, using dehumidifiers proved to be the best alternative. The entire process starts with a fish catch. The fish are prepared and split in half before the first-stage curing process of soaking them in a salt-water solution. They are then piled and rotated on pallets for another period during the second curing stage to begin the water elimination process. Finally, the fish are loaded on custom-designed portable racks before they are subjected to the tunnel process. There's no cooking danger with the mechanical process because drying is precisely controlled with a low temperature of 68 degrees F.

The dehumidifiers are controlled with Dectron's HT-800 microprocessor to provide three relative humidity stages ranging from 60 percent in the beginning to 25 percent at the end. "Although energy costs are constantly shifting because of the varying sensible heat ratio of the drier air throughout the cycle, our calculations tell us that 1-kwhr. is required to remove 4.25 pounds of moisture," said Jean-Guy Ferland, partner with Le Groupe Prodapec and designer of the LLL tunnel installation.

Dectron, Inc., 995 Mansell Rd., Suite B, Roswell, GA 30076. Tel. (770) 649-0102; fax (770) 649-0243; www.dectron.com