Food Packaging:
Retort pouches with zip

First commercial food applications are expected sometime this year.

RECLOSABLE CONTAINERS FOR RETORT MAY BE THE FINAL frontier for the flexible pouch. With development time lines that resemble NASA projects behind them, zipper manufacturers have crossed that frontier and anticipate the first commercial food applications sometime in 2004.

Standard resealable pouches don’t stand up well to the retort process (above), so Zip-Pak engineered a new zipper for those foods.
Conventional zippers are made of low-density polyethylene that won't withstand retort temperatures, forcing zipper manufacturers to design zippers made from polypropylene resins and match them with compatible pouch film. It also meant gaining FDA approval because of the residuals produced by the resins used. For Zip-Pak International, it added up to a five-year development process, according to Robert E. Hogan, director of sales and marketing at the Manteno, Ill., firm. The extruded closure is very stiff until it is retorted, after which it becomes supple, he says.

Aesthetic considerations also had to be addressed. Because food migrates to the edges of the pouch during retorting, engineers had to design a secondary barrier to shield the zipper and prevent food from crusting around it. Both Zip-Pak and Presto Products in Appleton, Wis., addressed the issue with multiple designs, depending on how the pouch is filled.

For top-fill pouches, Presto's Fresh-Lock engineers came up with an elongated flange that is sealed to the pouch wall and creates a barrier to product migration, according to Product Manager Tom Winter. For bottom-fill pouches, a unique membrane is incorporated into the design.

An elongated flange prevents product from leaching into the closure of Fresh-Lock's retortable zipper.
"Several products using the retort zipper are currently in test in Mexico, Europe and Japan," says Hogan. "There's a lot we still need to do in terms of testing the pouch production process to make sure it's suitable for commercial application." Zip-Pak is working with several converters of pre-formed pouches, including Kapak Corp. and Valley Packaging.

Fresh-Lock's partner in reclosable retort pouches is Pyramid Flexible Packaging. "There's major interest from U.S. manufacturers of soups, stews and other foods, but pet food is probably a safe bet" to be the first commercial product in the U.S. market, predicts Winter.

Pet food was the first non-MRE application of the retortable pouch, Hogan points out. Even greater potential may exist with large pouches for foodservice operators, he believes.

For more information:
Thomas A. Winter, Presto Products Co., 920-738-1747,

Robert E. Hogan, Zip-Pak International, 800-488-6973,

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