Is There A Difference Between Sour And Spoiled Milk?

Understanding the differences between sour milk and spoiled milk can be a bit confusing. After all, the word "sour" often refers to something that's gone bad, especially in the case of food. Still, sourness isn't always a bad thing, as we see with milk. In fact, some recipes even call for sour milk. So, what exactly is it?

Even though the words "sour" and "spoiled" are often used interchangeably when discussing milk, sour milk is technically unpasteurized raw milk that has begun to ferment (via Healthline). There are people who believe this type of sour milk may have certain health benefits since some species of bacteria that ferment it are natural probiotics. However, in the kitchen, sour milk can also be milk that's been soured with the addition of an acid, such as lemon juice or vinegar. It's the perfect substitute for buttermilk.

When milk has gone sour, there's no need to throw it away. Spoiled milk, however, is a different issue. Once your milk has spoiled, it may not be safe to drink or use.

When milk is spoiled, it is no longer useful and can even be harmful. Niket Sonpal, MD, a gastroenterologist and internist, told Well + Good, "Typically, if you ingest enough spoiled milk, it can basically take a really, really bad toll on your gastrointestinal tract." Most brands of milk you buy in the grocery store are pasteurized, making them safe to drink. Still, there are always some bacteria left that are not killed off. As the milk ages, these bacteria multiply and eventually lead to spoilage. Understanding the signs of spoiled milk is important so you don't accidentally consume it or ruin a recipe with it.

You'll likely know quickly if your milk is bad. First, your nose will tell you. Spoiled milk smells gross. It's beyond sour and can have an almost sewage-like odor to it. When you pour spoiled milk, chunks or curds may come out. That should be enough to make it clear and stop you from drinking it. If not, the last test is to sample it. A small taste of spoiled milk is all it takes to know that it's no good.