How to Make Buttermilk (sour milk)

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Picture this… you find a recipe you want to make… something that requires buttermilk… for example:

And you happen to be fresh out of buttermilk… or better yet, you have never bought buttermilk in your life. It happens to the best of us! But… what you may not know is making buttermilk (aka sour milk) is super simple and you probably have the ingredients for that!

What is Buttermilk?

Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream; most modern buttermilk is cultured, however. It is common in warm climates where unrefrigerated fresh milk sours quickly. What is sold in stores today is cultured buttermilk. They make this by adding lactic acid bacteria to regular milk. Buttermilk has a “sour” taste to it. This is why the substitute can be referred to as sour milk. It can be drunk straight (although most don’t) or used in cooking and baking to give a nice tang to your food.

Can I substitute Milk for Buttermilk?

Well… yes and no but more so no. First off, buttermilk is less liquidy than milk so if you substitute buttermilk for milk, you need to add a few more tablespoons of buttermilk. On the flip side… if you require buttermilk and use regular milk, you’ll have to remove those couple tablespoons.

But here’s the real kicker, especially in baking… Buttermilk reacts with rising agents, like baking soda and baking powder, to form carbon dioxide and act as a leavening agent. If you have a recipe that calls for both buttermilk and a rising agent, you shouldn’t substitute regular milk. This is where you can either buy Buttermilk from the store or make your own.

Things to Consider before buying Buttermilk

  • How much do you really need? Is it cost-effective if you throw the rest away?
  • Do you have milk and either vinegar or a lemon at home?
  • Do you have the right type of milk at home to make your own?

These are all good things to consider. There is also an option of buying powdered buttermilk to keep in the pantry so you can make it up as you need it. Definitely do what is best! But in a pinch, let’s just make our own Sour Milk.

How Long does Homemade Buttermilk Last?

So you’re looking at the same shelf life for your homemade buttermilk (sour milk) as your regular milk. So look at the expiration date on the carton. I have read that if you have store-bought buttermilk, it lasts longer than the expiration date on the carton, but I’m not sure how valid that is… so do research on that before you believe that! Remember, if it’s on the internet it has to be true, right?

How to Make Sour Milk


  • 1 cup less 1 tbsp milk (this can be skim, 1%, 2%, or even full fat)
  • 1 tbsp white vinegar or 1 Tbsp Lemon (not both, just 1 of either)

Place the milk in a measuring cup. It is best to remove that 1 tbsp of milk so you have room for your vinegar or lemon juice. Then add the 1 tbsp lemon juice or white vinegar. Allow to sit for about 5 minutes. Stir and use. Simple as that!

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