The date on the outside of the carton might not exactly reflect how fresh (or spoiled) your milk is. That's the "sell-by" date, which isn't an indicator of safety, and the milk inside still might be fresh in the days to follow, according to the USDA.
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That said, you could end up with expired or spoiled milk if your milk is stored or handled incorrectly — but there are a few key ways to tell.
Why Does Milk Spoil?
Milk doesn't last forever, so even if you suspect the carton of milk past its expiration date in your fridge is still fresh, it will spoil eventually.
"Milk spoils because of an overgrowth of microbes over time," explains registered dietitian Jenna Volpe, RDN, LD, CLT. "The microbes start to ferment particles in the milk, which allows them to multiply and compromises the quality and taste." You may notice milk smells or tastes sour when it's spoiled.
Most milk sold at grocery stores has been pasteurized — a process of heating the milk to kill off pathogens, according to the Food and Drug Administration (FDA). But even this process can't kill all the bacteria, and when the bacteria left behind continue to grow, they eventually cause milk to spoil, according to August 2018 research in the Journal of Dairy Science.
The sugar in milk also makes it susceptible to spoiling. Milk contains lactose, a sugar that allows bacteria to grow and multiply, which leads to spoiled milk, according to the Missouri Poison Center.
Though refrigeration delays milk from spoiling, it can only preserve milk for approximately seven days, according to the USDA. "Milk spoiling is inevitable, even when pasteurized and when stored at refrigerated temperatures," Volpe says.
How Long After the Expiration Date Can You Drink Milk?
When you buy milk from a grocery store, it's usually labeled with a "sell-by" date, which informs the store of how long to keep the milk on store shelves. These dates aren't indicative of safety but rather refer to quality, so it's generally safe to drink milk a couple of days beyond these dates, according to the Dairy Council of California.
You can drink milk up to a week past its sell-by date, according to Washington State University. Be sure to give it a taste and smell test before drinking.
Those with compromised immune systems may want to practice an even stricter policy. Volpe doesn't recommend drinking old milk out of the refrigerator if you have gut or immune system issues. Instead, try incorporating it into cooked dishes like frittatas or muffins, which may help sterilize any harmful bacteria, she says.
How Long Does It Take for Milk to Spoil?
Milk that is stored properly can last for several days past the printed sell-by date before it will spoil, according to Northwell Health.
You'll want to keep the refrigerator temperature at or below 40 degrees Fahrenheit, according to the FDA. Refrigeration at this temperature slows the growth of bacteria, which leads to spoilage.
You should also store milk in the coldest part of the fridge instead of the door, per the Academy of Nutrition and Dietetics.
Milk spoils much faster at room temperature. Perishable foods like milk have a two-hour rule — they shouldn't be left at room temperature for more than two hours, per the FDA.
For the widest window before milk spoils, choose one with the furthest sell-by date at the grocery store. It's freshest until that date, but since that date doesn't indicate safety, it may be safe to drink up to a week later if stored in a cold refrigerator.
How to Tell if Your Milk Is Spoiled
After the sell-by date has passed, you'll want to use your senses to determine whether the milk is still safe to drink. "Spoiled milk will usually have a sour odor and taste," Volpe says.
A good way to check milk for freshness is to give it a sniff. When milk spoils, the odor is typically strong and pungent. Even taking a small taste can help you determine if milk has gone bad. Other sure signs of spoiled milk are a moldy appearance and lumpy texture, according to the Cleveland Clinic.
After you buy your milk from the grocery store, try to refrigerate it immediately. Don't leave it in the car, especially if it's a hot day. Also, avoid leaving milk containers out on countertops or tables for long periods of time.
If you're ever unsure as to whether or not your milk is spoiled, it's probably wiser to toss it — better safe than sorry!
What Happens if You Drink Spoiled Milk?
Unfortunately, drinking spoiled milk can take quite a toll on your digestive system. Food poisoning is no joke and can cause vomiting, stomach cramps and diarrhea, per the Missouri Poison Center.
Symptoms can occur several hours — or even several days — after drinking spoiled milk. Most often, food poisoning is mild and symptoms will pass within a day or two. Reach out to your doctor if you think you have food poisoning from spoiled milk and your symptoms persist.
In some cases, especially if you drink raw milk, food poisoning can be more concerning, according to Kids Health. If the symptoms persist or you begin to experience signs of dehydration, it's probably best to take a trip to the doctor.
Your doctor can test for potentially harmful germs like salmonella or E. coli and recommend different treatments depending on the results.
- Dairy Council of California: "Milk Handling and Food Safety"
- KidsHealth.org: "Food Poisoning"
- FoodSafety.gov: "Drinking Raw Milk: It's Not Worth the Risk"
- Food and Drug Administration: "The Dangers of Raw Milk: Unpasteurized Milk Can Pose a Serious Health Risk"
- Journal of Dairy Science: "Psychrotolerant spore-former growth characterization for the development of a dairy spoilage predictive model"
- AskUSDA: "How long can you keep dairy products like yogurt, milk, and cheese in the refrigerator?"
- Missouri Poison Center: "Spoiled Milk"
- Dairy Council of America: "Drinking Milk Past Its Use-By Date"
- Washington State University: "Decoding Food Dates"
- Northwell Health: "Has My Milk Gone Bad?"
- FDA: "Are You Storing Food Safely?"
- Academy of Nutrition and Dietetics: "Keep Your Dairy and Egg Products Safe"
- Cleveland Clinic: "Trash It or Eat It? The Truth About Expiration Dates"
- USDA: "Food Product Dating"
- Dairy researchers identify bacterial spoilers in milk
- Milk, Cheese, and Dairy Products
- Can You Drink Milk Past Its Sell-by Date?
- Food Poisoning