Photo by: Kassa Zakadi/NBC
In Too Afraid to Ask, we’re answering food-related questions that may or may not give you goosebumps. Today: How long does milk last on the counter?
You’re basking in your daily dose of dopamine, mindlessly scrolling Instagram as you slosh some milk into your morning coffee. After what feels like hours, your thumb exhausted from double-tapping, you realize the carton of milk has been sitting on the counter this whole time. Panic sets in. You wonder, How long has it been? And then, naturally, Wait, how long can milk sit out?
Milk, the creamy cornerstone of countless breakfasts, beverages, and baking projects, isn’t immortal. It has a life span, and like all good things, eventually meets its demise. When it’s spoiled, you’ll probably know: Sour milk is a sensory assault. Signs of spoilage can include sharp, vinegary smells and a curdled and clumpy appearance. “The yuck factor is high,” says Nicole Martin, PhD, a food scientist and dairy researcher at Cornell University’s College of Agriculture and Life Sciences.
The good news: How you treat your milk—whether it’s cow’s milk or nondairy milk—can influence its mileage. Here’s how to keep your current bottle fresh.
How long can you leave milk out of the fridge?
The Food and Drug Association’s (FDA) general rule for most perishable foods is: Don’t leave them out of the fridge for more than two hours—even less if the room temperature where you are is hot. But it’s not a perfect science; there are ample factors that determine how fast your milk might spoil.
Why does milk spoil?
Milk’s vulnerability to spoilage stems from the fact that, in its raw form, it’s thronging with microbes. The main types present in dairy are:
Lactic acid bacteria: These friendly microbes are the workhorses of the dairy world. They convert milk sugar (lactose) into lactic acid, giving yogurt, cheese, and buttermilk their tang and gut-health benefits.
Thermophiles: Heat-resistant bacteria that, though mostly harmless, can throw a feral house party in your milk when you leave it out—producing those classic fart flavors and clotted textures.
The majority of milk you’ll buy in US supermarkets is pasteurized, meaning it’s been heated to temperatures that kill most pathogens. There are different types of pasteurization, but the most commonly used in the US is High Temperature Short Time (HTST), which reaches a temperature range of 161–165°F (72–74°C) for 15 seconds, says Michael Doyle, a Regents Professor of food microbiology at the University of Georgia. Pasteurization won’t kill all bacteria, though.
Known as spoilage bacteria, strains like Bacillus and Clostridium have a special trick up their sleeves: They can form heat-resistant spores, essentially dormant versions of themselves encased in a tough, protective shell. These spores tend to survive harsh conditions like extreme temperatures (pasteurization), drying, and even some disinfectants. The spores struggle to proliferate in the cold, but can come to life and rapidly multiply in temperatures between 40°F (4°C) and 140°F (60°C), what’s known as the “danger zone,” increasing the risk of spoilage.
Raw milk will go bad even faster. I’m talking about the unpasteurized stuff straight from the cow, which, despite being illegal in some states, is growing in popularity in the US due to claims that it’s more nutritious. Raw milk can also lead to serious illness. That’s because it’s more likely to contain pathogenic bacteria, the baddies that cause foodborne illness. Generally, due to a higher bacteria content, it’ll also spoil faster when left out of the fridge.
“I am a strong proponent of consuming only pasteurized milk, especially in regards to children and those with compromised immune systems,” cautions Jeff Bender, DVM, MS, ACVPM, a professor and public health veterinarian at the University of Minnesota.
Unopened milk, if stored correctly, can also last longer than opened milk. “Open containers are a bit like the wild west,” says Martin. “They are exposed to the environment in your home, so they may pick up additional microorganisms when the cap is off.” These interlopers can contribute to faster spoilage, especially when exposed to higher temperatures. A full bottle of milk will also stay colder longer than a half-finished one.
And if your mom told you not to slug milk straight from the bottle, there’s a good reason. It’s basically like double-dipping at a party; some of your mouth bacteria are almost certainly going to swim back into the milk.
Do alternative milks, like oat milk and almond milk, spoil out of the fridge?
The short answer is yes. While vegan alternatives to milk typically do not have residual bacteria, because they’re processed at higher temperatures than most dairy milk, leaving your oat or almond milk out of the fridge “accelerates enzymatic processes that can result in spoilage,” Martin says. (Enzymes are nature’s catalysts, which can speed up the breakdown of foods.)
It’s important to note that some alternative milks, and regular dairy milks too, are shelf-stable due to processing techniques like ultra-high temperature (UHT) pasteurization. You’ll find these cartons in unrefrigerated supermarket aisles, and they are generally fine to leave out until opened (just check the expiration date). But once opened, they still need to be refrigerated and the spoilage rules apply.
Is drinking spoiled milk unsafe?
Here’s the thing: You’re probably not going to drink spoiled milk because it tastes completely foul. Doyle says spoilage is “kind of a built-in safety measure.” If you did drink a little, though, “there is very little risk of it making someone sick,” says Martin.
To be clear, consuming milk that’s contaminated with pathogenic bacteria (like Salmonella, Listeria, or E. coli)—whether unpasteurized or adulterated somehow post-production—can lead to more severe food poisoning. But these bacteria “do not cause perceivable changes in the quality of the product,” says Martin, meaning they won’t affect the taste or smell, and it’s impossible to gauge the risk factor.
What’s the best way to store milk?
Ensuring milk stays fresh and safe for consumption involves more than just tossing it into the fridge. Here are some practical tips:
Avoid storing milk in the refrigerator door, where the temperature fluctuates more than inside the fridge on a shelf.
Keep your fridge cold. Monitoring the internal temperature ensures it consistently hovers around the recommended 37°F (3°C). Any deviation can compromise milk’s freshness.
Sterilize your containers: If you are, for any reason, transferring milk from the carton or bottle to another container, ensure it’s clean and sanitized first.
Keep the spout clean: After pouring milk, wipe the cap and opening to prevent residue buildup, which can harbor bacteria that’s transferred inside the bottle.
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Originally Appeared on Bon Appétit
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