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.

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.