Milk is one of the most popular drinks in the United States, with people consuming about 134 pounds per year in 2021.
That’s a lot of milk, mainly because about 12% of Americans are lactose intolerant and tilt the average. And that’s not including other milk products (like cheese on pizza) either.
(For more information on the difference between lactose-free and dairy-free, check out our guide to that.)
That said, most people buy milk by the carton, usually in a half-gallon or full-gallon size, and I know I’m not going to drink that much milk in one sitting.
So, how long is milk good after opening it? Well, that depends on a few factors, including the type of milk and how long it’s been in the carton.
Let’s take a closer look at the fine details here.
Expiration Dates
The easiest way to tell when milk will go bad is by looking at the expiration date. Unfortunately, some companies aren’t very buyer-friendly about this.
Most manufacturers use one of four standard labels for their milk’s expiration date.
The first is Expires On, which lists a specific date the product is guaranteed to be good. Expires On is a user-friendly label because it tells you a minimum for how long you have. Most milk will last a little past this date because the manufacturer wants to guarantee that the date is valid. They set it a little early to cover themselves.
The next option is Sell By, which is mainly for the store. Sell By isn’t helpful because it doesn’t say when the manufacturer thinks it will go wrong, only that it’s likely to start spoiling soon. If you see milk with this label and the date is close, consider looking for a different bottle, especially if you don’t go through milk quickly.
Use By sounds like it’s another version of Expires On, but it isn’t. Instead, the Use By label indicates when the product is at peak freshness, and it will start to go down from there. However, milk usually lasts quite a while beyond its peak freshness, so it’s another label that isn’t helpful for quickly uncovering the date.
Best Used By is similar to Use By, but it means the product is still safe even a little after that date. It’s another case of manufacturers trying to cover themselves for potential problems.
However, all of these dates only apply to unopened cartons. Once you open the milk, the clock starts ticking faster.
Milk After Opening
Most milk brands, though not all, have an additional notation on the carton that says how fast you should use the milk after opening it. The most common label is seven days, but that’s not exactly an industry standard.
If you open milk more than a week before its expiration date, it’s probably fine until that point as long as there’s no contamination. If it is contaminated, it can be sour within a day of opening.
I’ve been there, and let me tell you, I wasn’t happy about losing most of a gallon.
As long as the milk still smells reasonably fresh, though, it’s probably safe to consume even if it’s been over a week. I wouldn’t leave an opened carton in the fridge for two months, though. Don’t open milk unless you’re planning to use it soon, and adjust your meal plans if necessary.
If you have trouble getting through milk, try buying smaller containers. It’s better than letting too much go to waste.
Checking For Spoilage
Most people run with the seven-day rule for drinking milk after opening it, but it’s best to check milk for spoilage every time you use it after opening it.
That offers an extra layer of security, and if you don’t notice anything, you can probably keep using it until something changes.
Here are a few things you can check for to see if your milk’s gone nasty.
Curdling
Curdling occurs when milk becomes acidic and form protein lumps. These gather together and rise to the surface of the milk. Your milk should always be smooth, so if you see any curdling, it’s too old, and you should get rid of it. The milk won’t get better if you try to strain out the clumps and put the rest back.
Odd Coloring
Milk is always smooth white until it goes sour. If there’s a problem, it usually turns yellow, and that means it’s time to get rid of it. If you see something even stranger, like a black color, that’s added reason to toss it. Black could be a sign of mold or other contamination beyond simply going bad, so try to avoid breathing any of that in.
Solid Chunks
Similar to curdling, you may find solid clumps of protein on the sides of the container. The difference is where they are rather than what they are, as protein from curdled milk usually floats on the surface instead.
Sour Smells
Taking a quick sniff each time you open your milk is a good idea. Milk usually has a mild smell, so you shouldn’t notice much. However, if anything smells sour or otherwise unpleasant, your milk’s probably gone bad. If in doubt, throw it out.
Time Outside The Fridge
Milk starts going sour in about two hours at room temperature or one hour at ninety degrees or more. The bacteria naturally present in milk grow the fastest in warmer temperatures, and the longer your milk is out, the worse.
This is one of the main reasons you should keep your milk in the fridge as much as possible rather than leaving it out during a meal.
What Makes Milk Go Bad
The primary thing that makes milk go bad is an increase in any fungi, bacteria, or parasites present. That may not sound tasty, but don’t freak out just yet. Our bodies will be well if these are only present in small amounts. It’s only when you consume too many of them that milk is dangerous.
When these infestations grow, they start metabolizing the stuff inside the milk, especially the proteins. In doing so, they’ll change milk’s smell, appearance, texture, and flavor, which is why we can use those to judge when the milk’s gone bad.
Most modern practices follow a set protocol for making milk safe. Once it’s milked, the producer stores it in a refrigerated tank, allowing the low temperatures to limit the growth of microbes.
Of course, as we know from the way milk goes bad in the fridge, just keeping the temperature low only does so much. That’s why companies pasteurize it, which involves heating it to a little under boiling to help get rid of bacteria. Pasteurizing doesn’t eliminate bacteria, but it does get rid of most of them.
After that, companies usually homogenize milk, which evens out the size of fat chunks to create a consistently smooth texture. After that, as long as the milk stays cold, it’s ready to ship.
Effects of Spoiled Milk
Most people can tolerate drinking a small amount of spoiled milk. For example, if you open a carton and drink straight from it, only to realize the flavor is off, you’re probably fine if you spit out what you haven’t swallowed and toss the rest.
If you drink more, you can expect some stomach pain, nausea, and diarrhea as symptoms. Some people also find themselves vomiting, which is usually your body’s way of trying to get rid of pathogens.
Most symptoms of drinking spoiled milk will pass in a day at most. However, if you’re feeling too sick, make sure to contact your doctor.
Extending Milk’s Shelf Life
How long is milk good for after opening, but more importantly, can we do anything to change that time? There are several ways to extend milk’s shelf life and ensure it stays fresher in your fridge. You can’t do this forever, but it can serve in a pinch.
Freezing
Most milk can survive freezing for about six months, though you should make sure it’s in a container that can handle it. Frozen milk tends to turn a little yellowish because the ice chunks push the protein and fat together, but it’s still safe to drink once you thaw it out.
Freezing is also great at inhibiting the growth of bacteria. Milk isn’t a good candidate for things like flash freezing, but since it’s usually cold to start with, getting it just below freezing temperatures rarely takes long.
Storage
The best place to store milk in a fridge is towards the back. This area is the most consistently cold, unlike the front areas of the fridge, which see frequent temperature fluctuations. Incidentally, this is the same logic for why it’s better to store frozen meat in the back of a freezer.
Unfortunately, many people prefer keeping milk at the front of the fridge for easy access. That’s fine if you go through milk quickly, but if you expect to use it slower, keep it at the back.
Salt It
Yes, I’m serious, and no, I’m not crazy.
Salting may sound wild, but sodium can bind to water molecules. This limits bacteria’s ability to access it, slowing down the growth of pathogens. It’s not a good long-term solution, but for a short inhibitor, salt is surprisingly effective.
What About Plant-Based Milk?
Plant-based milk arguably doesn’t deserve the name because they don’t come from animals. On the other hand, many of them are quite healthy, and they’re worth considering as options.
Plant-based milk has different expiration speeds, so it’s best to check the packages for more information. As a general rule, however, plant-based milk almost always lasts far longer than traditional dairy options. This makes them an ideal choice if you tend to go through milk slowly.
As a rule of thumb, almond milk is usually good for at least four weeks past any Sell By date on the label.
Final Thoughts
So, how long is milk good for after opening?
Most milk is safe for at least a week after you open the carton, assuming no additional contamination and good storage conditions.
It can last significantly longer, but it’s always better to check the milk for spoilage each time you use it.