Food Engineering

Susceptors and the safety challenge

June 1, 2011
With the microwave supplanting the convection oven, package engineers eye susceptor systems to better protect frozen-food consumers from undercooked products.

Freezer abuse that can warp susceptor patches is overcome in containers of Red Baron pizza singles, an advancement that netted Graphic Packaging International the technical award in food packaging from AIMCAL.


More than nine in 10 US homes are equipped with a microwave oven, a saturation level that greatly enhances the convenience of frozen foods. That category is experiencing uneven growth but positive results where microwave product and package innovation have been strong, according to Mintel International Group Ltd., which pegs sales of frozen pizzas, entrées and snacks at $12.5 billion.

But uneven heating and the limited temperatures achieved by home microwaves can pose a public health risk, particularly when the ingredients in a microwavable meal are partially cooked or blanched. In the wake of 2007’s Salmonella outbreak linked to turkey and chicken pot pies that sickened more than 400, frozen-food marketers added explicit cooking directions, including a recommendation to use a food thermometer when microwaving to verify temperatures reach 165°F.

“It’s an impossible instruction,” frets Mark Etzel, associate professor in the Department of Chemical and Biological Engineering at the University of Wisconsin-Madison. Most Americans don’t know their microwave’s wattage, he observes, very few own a food thermometer, and “almost nobody obeys the standing-time” requirement. Admonishing people to “cook thoroughly” is a legal disclaimer that doesn’t address food safety, Etzel says. Without better food and package engineering, “it’s just a matter of time before there are [microbial] poisonings.”

Crisping and browning are the main microwave benefits of susceptors, though their ability to increase temperatures by focusing electromagnetic energy and causing greater friction of charged molecules is a functional advantage. Fully metallized film produces one heat output and is prone to undercooking the center and overcooking the edges of food. Demetallized film reduces the likelihood of overcooking but results in less browning and relatively low heat. Printed susceptors are prone to runaway heating, though engineers at Inline Packaging Inc. believe they have overcome the problem by including a metallization layer that cracks at high temperatures, thereby limiting or preventing the phenomenon.

“We’re designing the susceptor around the food,” says Jon Wolfe, application specialist at Princeton, MN-based Inline, allowing manufacturers to address a variety of quality and safety issues.

“There is a food safety component to susceptors,” allows Bob Babich, GPI’s business development manager, with their ability to achieve 165°F kill temperatures an important benefit. But browning, crisping and removal of excess moisture remain their primary functions.