The real purpose of aluminum or plastic food seals

A a quick search on Reddit will tell you that a lot households spend their time debating the purpose of aluminum or plastic seals on food items like yogurt and sour cream and whether they should be removed or kept after opening for extra cover. It was a lingering thorn for a couple for a decade until the husband found the solution in the most unlikely place: under the disposable seal that had sparked the debate. “A 10 year argument with my wife is finally over,” the Reddit user wrote at the time, sharing a photo of a seal the company had printed on: “To prolong freshness, completely remove and throw away that aluminum seal.”

It’s hard to argue with a guideline straight from the source, but it still raises a few questions. What is the purpose of aluminum or plastic seals on food containers in the first place? And how do you leave one on an open container spoil its freshness? In search of answers, we reached out to two germ experts.

The purpose of plastic wrap or seal on food containers

“There are two reasons for the seal,” says Jason Tetro, microbiologist and author of Germinal files. “First, it helps increase shelf life – the container is usually flushed with nitrogen before sealing, which reduces the amount of oxygen inside.”

According to Tetro, the second reason is to protect the contents of the container. “This helps prevent the introduction of chemicals and microbes that could spoil produce and/or cause illness,” he says.

Microbial ecologist Jack A. Gilbert, PhD, a professor at the University of California, San Diego, further explains that the seal is a safety and quality mechanism because it creates a barrier between the product and the external environment, while indicating to consumers that the product has not been altered before purchase.

Why do you want to remove the seal from your food container after opening it

“Break the seal”, a common term for the first time you go to pee while drinking alcohol to indicate that you’ve opened the floodgates – and there’s no turning back – is also applicable in this context as well. “Once the seal is broken, surrounding air and oxygen can enter the product and this will trigger microbial growth,” Tetro explains. “Whether the seal is still there or not is not a factor. Its sole purpose is to get it from the factory to your kitchen safely.

Additionally, keeping the seal on after opening the product can lead to an increased risk of contamination through continued contact, according to Tetro, which recommends removing the seal as soon as you open the product. If you have to leave it on for some reason (ahem, I can’t admit defeat), he advises you to wash your hands before touching it. But you’d better just accept that the seals were meant to be broken…and thrown away.

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