Oat Milk Left Out Overnight: Is It Safe to Use?

So, you had a late-night cereal eating extravaganza, and a great time was had by all (mostly just you, alone). But there’s one problem: You left out your oat milk! Now it’s morning, and you’re wondering: Is this oat milk still safe to use?

Oat milk left out for more than two hours (including overnight) should be discarded unless it is in an unopened, shelf-stable package. Even if the oat milk does not show signs of spoilage, it could have unsafe levels of bacteria and toxins produced by those bacteria.

Below, I’ll give you the full explanation of why it’s potentially unsafe to use oat milk that was left out overnight. I’ll also clarify which oat milks are shelf-stable, how long they can be refrigerated after opening, and more.

Shelf-Stable vs Refrigerated Oat Milk

The first important thing to realize with this issue is that there are two types of oat milk you can buy in the store: Shelf-stable and refrigerated.

  • Refrigerated oat milk is found in refrigerators or “cold” areas in the store. It usually has a cardboard carton, like an old-school milk carton. You need to keep it refrigerated at home, even if it’s not opened yet.
  • Shelf-stable oat milk is found on the shelf in the store, not refrigerated. It usually has a “Tetra Pak” container, and it’s usually smaller than the refrigerated ones. You don’t need to refrigerate shelf-stable oat milk until it’s opened.

Keep in mind that most of this blog post is about (1) refrigerated oat milk and (2) shelf-stable oat milk after it has been opened. Those are the cases in which your oat milk is perishable.

If your oat milk is still unopened in a shelf-stable Tetra Pak, then you don’t need to refrigerate it yet. It’s fine to leave it out at that point, even for weeks or months.

So now, let’s answer some questions about how to handle your perishable oat milk.

How Long Can Oat Milk Sit Out Unrefrigerated?

Here is the official answer, based on USDA recommendationsOat milk should not be consumed if it was left out for more than two hours. This applies to refrigerated oat milk or shelf-stable oat milk after it has been opened.

Temperatures between 40 and 140 °F are often referred to as the “Danger Zone.” In this temperature range, bacteria multiply quickly, and these bacteria can make you sick. (source)

If it’s extra hot in your house (over 90°F or 32°C), then the rule is only one hour. After merely one hour left out in those hot temperatures, oat milk should be discarded. This applies if you leave a carton of perishable oat milk in a hot car, for example.

“But I Do It All the Time…”

If you ask friends about this topic or read on Internet forums, you will hear from people who say it’s fine to use oat milk that was left out. Some will say they do it all the time and they’ve never gotten sick.

However, the FDA estimates there are 48 million cases of foodborne illness each year in the United States. Many people mistake food poisoning for something like the stomach flu.

So, it’s possible that many of these reckless folks have gotten sick from eating foods that were left out. They just didn’t realize the connection.

Some people may also tell you that if you boil the oat milk, that would kill any bacteria that had grown. First, that seems weird to boil oil milk. But secondly and more importantly, this is misleading.

Boiling will not rid oat milk of all possible toxins that were created by bacteria—even if the boiling kills the bacteria itself. Some bacteria, like Staph, produce toxins that are heat resistant.

Therefore, if you want to be on the safe side, you should just throw out the oat milk if it’s been left out overnight (or more than two hours).

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Can Bad Oat Milk Give You Food Poisoning?

What happens if you drink bad oat milk? Can you get seriously sick? Drinking bad oat milk could cause symptoms like nausea, vomiting, diarrhea, fever, and stomach cramps. (source)

As noted above, cases of food-borne illness are often mistaken for the stomach flu—so, think of those kinds of symptoms. However, depending on which bacteria have multiplied, how many there are, and other factors, the health consequences could potentially be more severe yet.

Personally, I do not recommend testing the boundaries with bad oat milk or any food products that have been left out. Remember, it’s just a few dollars to buy a new container.

Does Oat Milk Go Bad If Not Opened?

Oat milk will eventually go bad, even if not opened. However, shelf-stable oat milk will often last for months or years, much longer than refrigerated oat milk.

Unopened shelf-stable oat milk may have a “use by” date years in the future, while refrigerated oat milk will have a “use by” date only weeks or months in the future. Check the “use by” date for your specific oat milk container.

How To Tell If Oat Milk Is Bad

You may have heard some of the following common-sense ways to check if your oat milk has gone bad:

  • If the carton is bloated
  • If it smells bad
  • If there are clumps forming
  • If the color has changed
  • If the taste has changed

These may help you identify some cases of spoiled oat milk. But I would not rely on these signs alone to check my oat milk.

When it comes to oat milk that was left out unrefrigerated, you shouldn’t try to judge if it’s bad by using your senses. Instead, make the decision based on the number of hours it has spent in the “danger zone” of 40 to 140°F.

If it was in the “Danger Zone” for more than 2 hours, it should be thrown it out, according to USDA recommendations. Additionally, if it’s been open in the refrigerator for more than 7-10 days, it should also likely be thrown out.

Unfortunately, you cannot rely on your sense of smell and taste to know for sure whether oat milk has gone bad. As WebMD’s guide explains, “Food contaminated with the staph toxin may not look or smell bad, so you may not know to avoid them.”

This is further explained in a fact sheet from the FDA:

“You may be surprised to learn that food can make you very sick even when it doesn’t look, smell, or taste spoiled. That’s because foodborne illnesses are caused by pathogenic bacteria, which are different from the spoilage bacteria that make foods ‘go bad.'”

The document goes on to explain that many foods contain a small amount of pathogenic bacteria when you buy them from the store. So, all it takes is a few hours in the “danger zone” (40 to 140 degrees Fahrenheit), and those bacteria can multiply many times.

Here’s the takeaway: Don’t try to “figure out” if your oat milk went bad by looking at it, smelling it, or tasting it. You cannot accurately judge the levels of pathogenic bacteria that have multiplied by using your senses alone.

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Does Oat Milk Really Go Bad 7 Days After Opening?

Many oat milk containers may advise drinking it within 7 or 10 days of opening. But often, it will still look and smell fine at that point. So, what’s the deal? Is it okay to drink your oat milk on day 11 and beyond? Or not?

According to several experts who work for plant-based milk companies, 7-10 days is just a general, conservative guideline for perishable foods. If you’ve been diligent about keeping your oat milk closed tightly in the refrigerator, then it may last longer.

For example, a representative from Ripple Foods explained why they only guarantee their product’s safety for 7-10 days after opening. It’s likely that the product will still be safe after that, but it depends too much on environmental factors.

So, it may be a bit of a risk to consume oat milk more than 10 days after opening… But most of the time, it will still be fine if there are no signs of spoilage (covered above).

Keep in mind, as well, that homemade oat milk will only typically last around 3-5 days—not as long as store-bought oat milk.

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