There are about four different ways to make your own buttermilk, and the best method for you will depend on what you need it for, and how soon you need it.
Using the first two methods described below, you can make your own buttermilk in 10 minutes or less. The second two methods will take longer.
If you want to make a true cultured buttermilk, which is what you buy at the store, it will take about 24 hours, and you will need to start with either an active buttermilk culture or a cup of actual cultured buttermilk.
But if I had buttermilk, I wouldn't need to make my own buttermilk!
Quite right. So if you are looking at a recipe that calls for buttermilk, and you need some buttermilk right now, there are a couple of things you can do.
The main reason a recipe will call for buttermilk, apart from the tart flavor and creamy thickness that the buttermilk provides, is the acid. The acid in buttermilk is a byproduct of the fermentation process, and it will activate baking soda or baking powder, causing your bread or muffins or pancakes to rise.
If this is what you need, you have two techniques to choose from.
How to Make Buttermilk Quickly (Method #1):
This is a really easy method. Just add one tablespoon of lemon juice or vinegar to one cup of milk, and let it sit out at room temperature for about ten minutes. If you need more than a cup, just keep the ratios the same. For two cups, use two cups of milk and two tablespoons of lemon juice or vinegar.
As I noted, this method will not give you a true cultured buttermilk, but rather, acidified buttermilk. This means you can use it in a recipe for biscuits or pancakes or whatever and the acid will activate the baking powder or baking soda just as it should.
How to Make Buttermilk Quickly (Method #2):
Also a really easy method.
Just take ¾ cup of yogurt or sour cream and thin it out with ¼ cup of milk (or even plain water). This will make a cup of "buttermilk," although just like the first method, it's not a true buttermilk, but it will be an adequate substitute in whatever recipe calls for buttermilk.
If you aren't in a big hurry, or if you're just interested in the process, here are two ways of making your own cultured buttermilk. Unlike the two methods described above, which simply involve adding an acid to milk and letting it curdle, the methods described below will give you true, cultured buttermilk.
How to Make Real Cultured Buttermilk (Method #3):
The easiest way to make your own cultured buttermilk is if you already have some cultured buttermilk on hand. Here are the steps:
- Start with a ¾ cup (6 oz.) of cultured buttermilk in a very clean glass quart jar. Add 3 cups of whole milk. It does help if the buttermilk is fresh, because the live buttermilk cultures are more active in fresh buttermilk.
- Seal up the jar tightly, give it a good shake to blend everything together, and then let it sit at room temperature, like in your kitchen, for 24 hours. The ideal temperature range is 70–77°F. Up on top of your fridge can be a good spot.
- After 24 hours, the buttermilk will have thickened to where it will coat the inside of a glass, and it should have a pleasantly tart flavor. Refrigerate to chill or use right away, and store in the refrigerator, where it will keep for several weeks. Repeat the process as often as you like when you get down to the last 6-8 ounces of buttermilk.
The key here is the ratio of 4:1. You could use one cup of buttermilk and four cups of whole milk, but that won't fit in a quart jar. Even if all you have is two tablespoons of buttermilk left at the bottom of a carton, you can add four ounces of milk and wind up with five ounces of buttermilk, and you can just keep increasing it from there by repeating the process.
Or you could buy a quart of buttermilk and combine it with a gallon of milk to make five quarts of buttermilk.
The nice thing about this method is that you can keep repeating the process and theoretically never run out of buttermilk again. But you'd need to make sure that the buttermilk you use as your starter is always fresh.
How to Make Real Cultured Buttermilk (Method #4):
You can purchase active buttermilk cultures, usually in freeze-dried form, and use them to make your own buttermilk, basically by combining the culture with whole milk and letting it sit out for 12–24 hours, much like in Method #3 above. As with Method #3, you can keep repeating this method, using the last little bit of buttermilk to start the next batch.
Also see: What is Crème Fraîche?