Curdled milk is one of those things that you recognize instantly when you see it. With those infamous clumps and lumps popping up in your glass of milk — or in your cup of coffee — it's hard not to notice curdling when it happens. But is curdled milk bad? Does it mean that the milk has spoiled? Or is it a sign of something else entirely? Here's the short answer to all those questions: It depends.
Is curdled milk bad for you?
To understand whether curdled milk is "good" or "bad," we must first understand the difference between intentional curdling and unintentional curdling of milk. Let's start with intentional curdling: According to Scientific American, intentional curdling of milk is essential for the production of popular dairy products such as cheese and yogurt. In fact, it's usually one of the first steps of the process of making these tasty foods. There are a variety of ways to make milk curdle — such as adding heat or acid or simply letting the milk age long enough — but we can all agree that we're grateful for cheese and yogurt producers for doing the hard work for us.
As for unintentional curdling, well, that looks more like those infamous lumps and clumps that come from the milk carton in your fridge that's been sitting there too long. It sure as heck doesn't look good to us, but does that necessarily mean it's bad for our health? Well, it all depends on whether the milk has actually spoiled or not.
First of all, spoiled milk can indeed curdle. And trust us when we say this: You definitely don't want to drink spoiled milk. You risk exposing yourself to harmful pathogens if you do — some of which can cause a nasty bout of food poisoning. To find out whether your milk has spoiled, you'll need to do a sniff test. One of the biggest signs of spoiled milk is a sour odor. Next, check out the appearance of the milk while it's still inside the actual carton. If it's curdling in there, that's another sign it's gone bad. And of course, if you do a taste test and the flavor seems off in any way, it's definitely time to toss it. You don't want to risk getting sick, after all.
But what about curdled milk in coffee?
Curdled milk in coffee may be different from curdled milk in the carton. If it passes all the "tests" in the carton — it smells fine, it looks fine, and it tastes fine — there may be something else happening with the milk once it actually hits your coffee. According to Science Notes, milk sometimes curdles in coffee and tea because the acidity is just high enough to alter the pH of the milk. This usually happens when you add milk to very hot or acidic coffee or tea.
As Buzzfeed reports, the heat and acidity can also affect non-dairy milks such as soy milks in a similar way. Although this curdling is not necessarily bad for your health, it's also not exactly ideal (who wants to drink coffee with chunky milk in it?). The good news is that you can fix this type problem pretty easily: Just cool your coffee or heat up your milk before putting your tasty morning beverage together.
But beware: Milk can also curdle in coffee right before the milk is about to turn sour. Always be sure to thoroughly examine milk before you put it in your cup. And remember the old saying: When in doubt, throw it out.
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