Does Buttermilk Go Bad?

Buttermilk often smells and looks fine well beyond its expiration date, so how do you tell when it’s truly bad?

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I always keep buttermilk in the fridge, since I like to make pancakes and soda bread on a whim. More often than not, the buttermilk is well past its expiration date since the stuff always looks and smells perfectly fine for weeks. (Plus, we know those dates aren’t officially regulated and aren’t meant to convey anything about food safety.) I often joke with my family that buttermilk never goes bad.

Of course, it does eventually. There are obvious signs of spoilage like blue-green mold growth or when the buttermilk’s naturally sour aroma gets more pungent and its viscous body becomes gloppy. But does it start to spoil before those cues are obvious? 

In the test kitchen, we asked industry experts to weigh in on buttermilk shelf life and compared their input with our own experience. —Elizabeth Bomze

What Is Buttermilk? 

The term applies to a range of dairy products, but most commercial buttermilk is skim milk that manufacturers culture by adding lactic acid bacteria. The bacteria give the milk its thickness and distinctive sour aroma and acidity.  

How Long Does Buttermilk Last?

Buttermilk has a much longer shelf life than fresh milk because its abundance of lactic acid is hostile to the growth of harmful bacteria. But based on what we’ve learned from industry experts and our test kitchen experience, it doesn’t have a precise shelf life. 

  • The dairy farm that produces the buttermilk we use in the test kitchen told us to consume their product within five to seven days after opening. 

  • Guidelines from agricultural programs at various universities recommend consuming buttermilk within three weeks of the date stamped on the package. 

  • In the test kitchen, we’ve found that buttermilk won’t turn truly bad (signified by mold growth) until at least three weeks after opening.

Can You Freeze Buttermilk?

Absolutely. It freezes really well. Here’s an easy way to do it if you think you won’t finish the carton in time.

  • Pour buttermilk into an ice cube tray and freeze until solid.

  • Transfer buttermilk cubes to a zipper-lock bag and freeze until ready to use. 

Alternatively, there are so many good ways to use up buttermilk.

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