The answer depends on when you’re asking! First, let’s go back in time. A long time ago, people made butter at home. They got milk from a cow and churned the milk to make butter. Churning means that they mixed it for a long time. After mixing the milk for a long time, it would begin to separate. You would begin to see clumps of yellow, sticky butter. The liquid left over was buttermilk.
This traditional buttermilk was thin and watery. If made from fresh milk, this buttermilk would be sweet. Often, though, people would make butter from milk that was not very fresh. Without refrigerators, milk would go bad quickly. It would taste sour. Bacteria from cows would go into their milk. If people made butter from milk that was not fresh, the buttermilk would be sour.
This kind of buttermilk is an acid, which is what makes it taste sour. People began to use this sour buttermilk, along with baking soda or baking powder, as a rising agent in baking. A rising agent is something—like yeast—that helps a bread rise. Little air pockets in bread, pancakes, cake, and more, are due to rising agents. When we mix an acid (buttermilk) with a base (like baking soda), we get bubbles. These air bubbles are carbon dioxide created when the acid and base combine. The acid in buttermilk makes it a great rising agent.
Without a rising agent making air pockets, bread would be flat. Bread made with rising agents is also called “leavened” bread. Not all bread has to be leavened. Tortillas, roti, pita, and matzo are some examples of unleavened bread. Crepes—a kind of flat pancake—are unleavened, also.
Today, we mostly use buttermilk as a rising agent and do not drink it. If you have ever tried to drink it, you’ll know it is sour! But as our modern buttermilk has gone bad? No. Modern buttermilk is not made from churning butter. Instead, it is made by adding bacteria to milk. This bacteria causes milk to ferment. So while buttermilk itself isn’t alive, it is full of tiny living organisms—bacteria.
You may be wondering, why would anyone add bacteria to food. Aren’t bacteria bad for you? Some are, and some are not. Many bacteria are actually good for you! Good bacteria in our intestines play a vital role in helping us digest food. In fact, there are about 100 trillion “good” bacteria in our bodies! They help keep us healthy. Many even make important vitamins for us, like folic acid, niacin, and vitamins B6 and B12.
What happens without these good bacteria? Well, have you ever gotten diarrhea after taking an antibiotic? It’s a common side effect for many. The antibiotic kills off “bad” bacteria making you sick, but it also kills off a lot of “good” bacteria. Too few good bacteria can upset your stomach and give you diarrhea. You can give your intestines more good bacteria by eating certain foods. These include fermented foods like miso, tempeh, or kimchi. You can also eat yogurt, some kinds of cheese, and even—you guessed it—buttermilk!