Whether you like it or not, plastic packaging has become an integral part of the food system.
When we buy salads, sandwiches, and potato chips, we immediately throw away the outer layer of plastic packaging, which is really wasteful; but it is also this layer of plastic that keeps a lot of our food fresh during transit, and We never delve into this.
Many plastic packages allow us to eat while walking, or taste the perishable cookies and fish from the other side of the earth. There are actually a lot of scientific principles and inventions hidden behind them.
According to Aaron Brody, a food packaging consultant and associate professor of food science at the University of Georgia, the plastic revolution in food packaging began in the 1960s. So I chose plastic because it is lighter than glass, stronger than paper, and cheaper.
But Brody also pointed out: "Universal plastics do not exist." Many of the packaging bags we contact are made of different types of food packaging plastics.
Potato chips packaging bag
Take potato chips, for example, whose main ingredient is a plastic called "oriented polypropylene". Brody explained, "That's a good moisture barrier." Moisture barrier is very important in the packaging of potato chips. "Because potato chips absorb moisture, they will start to deteriorate. Wet potato chips won't Some people like it. "To further strengthen, many potato chip packaging bags also added a thin layer of aluminum to the inner layer.
The product name and nutrition information are printed on the outer layer, and a layer of polyethylene (the material used to make plastic shopping bags) is sandwiched between the inner and outer layers.
Brody also revealed that most companies will inject nitrogen into the bags before they are sealed. "This will prevent the potato chips from crushing." Oxygen will oxidize the fat in the potato chips and produce a strange smell, but nitrogen will not cause any chemical reaction that destroys the taste.
Brody also said that food companies often spend a lot of time designing packaging in order to best preserve every product they sell. This is also the practice of the military. In previous reports, the Army used a packaging to extend the shelf life of sandwiches to two years (read more: Sandwiches that have been kept fresh for two years, taste good).
Like the potato chip packaging bag, the ready-to-eat vegetable salad packaging bag is also made of polypropylene, and a packet of nitrogen is also injected. Unlike potato chips, salad leaves need to breathe a little oxygen, which is why there are small holes in the salad packaging bag. Brody pointed out: "The small holes allow oxygen to enter and carbon dioxide to exit."
He added that these bags often have a thin layer of anti-fog inside, "so that no condensation will occur and consumers will see the beautiful green leaves."
Ice cream bucket
When making many plastic packages, manufacturers worry not only about how to keep the air out, but also how to keep water vapor inside. For example, Brody said, this is important in the packaging of ice cream. A bucket of ice cream must be easy to open and close, but it must also have a tight seal that locks in moisture to maintain a smooth mouthfeel.
When stored in a refrigerator, sublimation sometimes occurs, that is, the phenomenon that water directly changes from a solid state to a gaseous state. "Once the sublimated moisture is lost, it cannot be recovered, and if the ice cream loses moisture, it will become sandy and agglomerated," Brody said.
He also pointed out that this is why a layer of polyethylene is added to the paper bucket that holds the ice cream. And the high-quality ice cream bucket is made of thick and strong materials.
Of course, as Herbert Stone, a food expert, puts it, even after all sorts of research and development, most plastic packaging still can't store food in extreme environments. Stone is a food industry consultant and a past president of the Food Technician Institute.
Stone pointed out: "When food companies use plastic containers, they must ensure that they do not change the taste of the food." He added that plastic is not an inert material and it can react with other chemicals. And unlike many glass or metal products, it allows air to pass through.
Have you ever left a plastic water bottle in a hot car for too long? Then it tastes weird. But the reason is different than you think: It's not because the chemicals in the plastic have penetrated the water.
Stone explained that trace amounts of air can penetrate the plastic, and when the temperature rises, the movement of the air will accelerate. Heat also accelerates chemical reactions. When the chemicals in the bottle react with each other or with the external environment, the water in the bottle will smell strange.
Leave a bottle of soda in the hot car and the carbonic acid in it will quickly escape from the bottle. "The rest is sparkling water," Stone said. "Plastic is convenient, but it is not a panacea."
In addition to its technical limitations, all the plastic packaging we use today generates a lot of waste. In 2012 alone, the United States produced 14 million tons of plastic waste that was once bags and containers. Plastic cannot be easily biodegraded, so it sometimes enters the ocean, which not only harms the creatures in the sea, but even pollutes seafood.
Although many types of plastic are already recyclable, bright packaging that contains multiple layers of plastic is difficult to recycle because different types of plastic are handled separately in the recycle bin.
But Stone revealed that we are also getting better at making plastics that are both easy to use and environmentally friendly. We're even trying to turn waste products like whey protein into plastic.