These Signs Mean Your Yogurt Has Gone Bad

Forget what those kids at the elementary school lunch table said — yogurt is cool. For starters, per Healthline, it's rich in calcium, vitamin B12, magnesium, protein, and potassium. Those are all crucial minerals to a healthy body, but they also boost metabolism and aid against chemical symptoms of depression. Nice. But that's not all.

In his magnum opus "Steal This Book," 1960s counterculture icon and antiwar leader Abbie Hoffman shared a detailed self-refilling yogurt recipe to fuel his followers. "Yogurt is one of the most nutritional foods in the world," he wrote. "The yogurt simply grows until the whole bowl is yogurt. Yippie! It will keep in the refrigerator for about two weeks before turning sour, but even then, the bacteria will produce a fresh batch of top quality. Remember when eating it to leave a little to start the next batch."

Yogurt is quite literally the fuel of the revolution — and, like the revolution, it replenishes itself. Here are some telltale signs to look for to make sure you're only fueling your body and mind with the best yogurt possible. Let's make sure that yogurt stays fresh and that you recognize the signs if it's gone bad.

Abbie Hoffman was pretty accurate with his explanation of the science behind yogurt. The biologists/yogurt aficionados at Yogurt Nerd offer a thorough breakdown. According to them, yogurt is fermented milk processed with cultures.

To make yogurt, lactic bacteria or live starter cultures are added to any heated, pasteurized milk. (The ideal heating temperature is 160 degrees Fahrenheit, per Cultures for Health.) After heating, the yogurt is left at room temperature for around eight hours so the bacteria can grow and convert the milk sugar or lactose into lactic acid. Lactic acid is the key ingredient that turns milk into yogurt: it brings the milk to that thick, creamy consistency we know and love.

No superhero is without a weakness. As About Yogurt explains, the key indicator of yogurt that's gone bad is an excess amount of water. What's tricky about this, though, is that the excess fluid from expired yogurt can be mistaken for whey, a sign of healthy yogurt culture. Often when you open a container of yogurt, you'll notice a thin layer of water on top — that's the "whey," and it's where all the nutrients are. But be careful not to stir the pot and dig in without carefully analyzing that layer. Whey typically runs clear, so if that water on top of your yogurt is looking a little cloudy, better play it safe and toss it out.

An easy way to verify your yogurt's freshness is to check the expiration date. While it isn't a foolproof indicator, the expiration date is a reliable frame of reference. According to Eat By Date, unopened yogurt has a shelf life of two to three weeks in the refrigerator, or one to two months in the freezer.

Yogurt that's been opened lasts for much less time: roughly one week in the fridge or less than a month in the freezer, so keep an eye on your leftover yogurt. Greek yogurt, on the other hand, is culturized with a slightly different bacteria, so it only has a shelf life of one to two weeks in the fridge, and one month in the freezer.

Expired yogurt will generally exhibit signs your senses will pick up on that the food has gone bad: a rancid, unappetizing smell or visible mold growth. As it deteriorates, yogurt will also release gasses that cause the container to bloat. Make sure you keep your eyes peeled.

So, worst case scenario and it's early in the morning, you're in a rush, or your judgment is otherwise just a little off — is it OK to eat expired yogurt?

It's not the end of the world. Amande Yogurt reports that refrigerated yogurt can be safely consumed within 15 days of the expiration date. Since yogurt is already made from bacteria-rich milk, the vegan brand explains an additional two weeks on the shelf shouldn't introduce any new harmful bacteria to the mix. Any longer than that, though, should be avoided.

But what about unrefrigerated yogurt? We've all gotten home from the supermarket and forgotten to put away a stray bag of groceries. According to Undeniably Dairy, yogurt will keep fresh for two hours at room temperature and for one hour if the temperature is at 90 F or above. This is especially important to consider when packing yogurt in a school lunchbox: be sure to add an ice pack to make it till lunchtime.

With these methods, your fridge will stay stocked with only the freshest yogurt — fresh as in ready to eat, but also fresh as in cool. Yogurt is an unsung rock star. So, you can tell Andrew from the third grade with the frosted fudge brownie wrapped in plastic that no, he was the one with the "weird lunch." You knew what you were doing all along. (Even if you didn't. We won't tell.)