The Weird, Underappreciated World Of Plastic Packaging
Like it or not, plastic packaging has become an ingrained part of the food system. And behind many of those packages that allow us to eat on the go or savor perishable cookies or fish imported from the other side of the globe is a whole lot of science and innovation.
“But there is no such thing as the perfect plastic material,” says Aaron Brody, a food packaging consultant and an adjunct professor of food science at the University of Georgia. So a lot of our packaging is made by combining different types of food-grade plastic.
Potato Chip Bags
Take a bag of potato chips. It’s mostly made out of a plastic called oriented polypropylene. “It’s an excellent moisture barrier,” Brody notes. And that’s key, “because potato chips first start to deteriorate by absorbing moisture. People don’t like soggy chips.” To further strengthen the material, many chip bags have a thin aluminum coating on the inside. A layer of polyethylene (the stuff plastic grocery bags are made of) is sandwiched between this inner layer and the outer layer, which displays the brand and nutrition info.
Like chip bags, bags of ready-to-serve salad are made of polypropylene, and packed with a bunch of nitrogen gas. But unlike chips, salad leaves need to breathe with a little bit of oxygen. That’s why salad bags have microperforations, Brody says. “The holes let oxygen come in and carbon dioxide get out.”
Have you ever left a plastic bottle of water in a hot car for too long? It’ll probably taste funny. But despite what you might think, that’s not because chemicals from the plastic are leeching into the food. Tiny amounts of air can pass though plastic — and when it’s hot, the air starts moving faster, says Herbert Stone, a consultant for the food industry and a past president of the Institute of Food Technologists. Heat also speeds up chemical reactions. And when chemicals inside the bottle react with each other, or with chemicals from the outside environment, your water can start to taste pretty funky, he says.
We are getting better at making effective and environmentally friendly plastics, Stone says. We’re even figuring out how to take waste products like whey protein and turn them into plastic.