Making sour milk at home is quick and easy.
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The Two Ways to Make Sour Milk

There are two ways to make sour milk at home: by acidification and by fermentation.

Acidification is the easiest and most economical way to make sour milk, as it only requires milk from the grocery store, an acidic ingredient (vinegar or lemon juice), and a little bit of time.

Making sour milk by fermentation is a lengthier and more involved process. It requires a starter culture and several hours of incubation in a controlled temperature environment.

Buttermilk is the most common type of cultured sour milk, made by fermentation. You can purchase buttermilk starter cultures for repeated or one-time use, or you can make buttermilk from milk and a small amount of store-bought buttermilk.

In the typical situation where you want to make sour milk as a quick substitute for buttermilk, making sour milk by acidification is the way to go.

sour milk going into blue bowl
Credit: Nadia Hassani

How to Make Sour Milk

Ingredients
1 cup milk
1 tablespoon white distilled vinegar or strained lemon juice

  1. In a jar or a small bowl, combine milk with vinegar or strained lemon juice. Stir and let it sit until the mixture thickens or curdles, about 15 minutes, or a few minutes more.
  2. Once the milk has the desired consistency, use it at once, or cover with a lid and refrigerate. Use within a couple of days and stir well or shake before using.

Makes 1 cup

sour milk in a jar
Credit: Nadia Hassani

Tips

  • You can make sour milk with fat-free, reduced-fat, or whole milk.
  • Use lemon juice or white distilled vinegar with 5% acidity, which has a neutral in taste and is colorless. In a pinch, you can use white wine vinegar. Any other vinegar is not suitable because it will give off its taste and color to the sour milk.
  • The lemon juice can be freshly squeezed or bottled. When using fresh, strain it to remove pulp and seeds.
  • Some recipes for sour milk list cream of tartar as an acidifier. While it does the job as a leavening agent, cream of tartar does not have the typical tanginess that you want from sour milk.
  • It is best to start with milk at room temperature. If the milk is straight from the fridge, it will need extra time. The amount of time depends on the ambient temperature, and the milk will thicken and curdle further if you give it more time. But it is not a good idea to let the milk sit on the counter for hours on end or overnight to sour, like it was done in the old days. The milk may go from sour to spoiled.
  • The acidification of the milk prevents the growth of harmful bacteria. But even if you turn milk into sour milk, the sell-by date on the bottle is still an indicator of when to use it. As a rule of thumb, any soured milk product should be consumed within one week after the sell-by date.
jar of homemade sour milk
Credit: Nadia Hassani

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