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I just came back from a long trip and I was cleaning out my fridge, and I noticed that there is an expiration date on the butter. It expired about two months from when I bought it. The butter doesn't look any different than normal butter.

How strictly should I follow the date on the box? Is there a way to test to see if the butter has actually gone bad?

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Butter can go bad. The oils will go rancid if exposed to too much light and heat for too long. This accelerates the process of oxidation, which happens even if you keep the butter in the fridge. Even in the fridge your butter will eventually go bad.

Personally I follow the dates on all packages. I do so with an awareness that they usually tend to be conservative, which keeps me comfortable. Rancid butter in a taste test won't kill you, though. It'll just taste bad. So you should be able to taste this butter to see if it is bad.

While I recommend following the dates on packaging, here are signs that your butter has actually gone bad:

  • discoloration
  • melting (which will happen outside of the fridge, you probably wouldn't see it)
  • sour smell
  • sour and unusual taste
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    +1, as I've had butter go bad in the fridge myself. Took a LONG time though (no clue how long). Generally I toss butter when discoloration get's too bad. Sour smell or taste is an immediate toss. – Tobias Op Den Brouw Aug 26 '10 at 12:56
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    I've kept it in the fridge for up to a year with no problems (it goes on sale between Thanksgiving and Christmas). Some recommend freezing for anything longer than six months: eatwisconsincheese.com/wisconsin/other_dairy/butter/… Of course, when cold-storing large quantities of butter, you should take fire-safety into account too: madisoneast.channel3000.com/news/news/… – Wayfaring Stranger May 13 '14 at 15:37
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    Also consider salted vs unsalted. Unsalted butter will maybe last a week or so during the summer before it goes bad on the counter (or in the winter, if you keep your house too warm). Salt acts as a preservative and can give you more time, maybe another week or so. The preservative properties of salt can also work in the fridge. FWIW, I still have a pound of butter in my fridge from last xmas, and it is discolored but not quite bad. I will probablly toss it soon and buy a pound to hold me over until baking season... – JSM Oct 8 '14 at 18:18
  • Since I buy my butter when it goes on sale, and keep it in the freezer, I don't think I ever even look at expiration dates. But I only have one stick salted, one stick unsalted, ever in the fridge at a time. Also, if you keep your butter not in a sealed container in the fridge, even if it doesn't go "bad," it's going to pickup odors from all the other foods, over time, and will taste off, even if it's not "bad" for you. – PoloHoleSet Aug 23 '16 at 20:08
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Yes, butter can go bad. Rancid, for instance.

This question has been treated before in this possible duplicate - does that help?

  • @Tobiasodenbrouw - seems like a somewhat different question (with related answers), since one was about leaving butter out and this butter was in the fridge. – justkt Aug 26 '10 at 12:53
  • Yeah, it's a bit different. Still, the link doesn't hurt. – Tobias Op Den Brouw Aug 26 '10 at 12:55
  • @Tobiasodenbrouw - definitely, just wasn't sure how to take the phrase "possible duplicate" – justkt Aug 26 '10 at 12:58

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