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I've got about 15lbs of saphire unbleached white flour left from my 25lb bulk purchase from 2 weeks ago. While preparing a wonderful zucchini bread recipe I noticed a "sour" smell from my flour.

It's been tightly sealed in the heavy duty bag I purchased it in and stored in the pantry at 70-85°F.

  1. Has my flour spoiled?

  2. What are the storage guidelines for flour?

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up vote 6 down vote accepted

The smell is of rancid fats in the flour. It is a very distinct smell, but hard to describe. I would agree that "sour" is part of it. The best way to learn is by comparison. Smell some fresh, clean flour and remember what it is like. Any kind of unpleasant odor than that is rancidity. You may have smelled it also if you opened a box of cereal that has been around too long, or even poppy or sesame seeds - anything with fats that sits around at room temp will eventually go rancid.

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So...toss it? And next time freeze/fridge it? – Michael Haren Aug 21 '10 at 15:55
It depends on how fast you go through it. For whole grain flours, which have more fats left in them, I recommend the freezer unless you use them quite quickly. And yes, definitely dump any rancid flour. It tastes horrible and it is bad for you. – Michael at Herbivoracious Aug 22 '10 at 3:19

I have also had flour go moldy (actually last week) and it was held in a pantry area I think that was a bit too warm and humid. It had a funky smell and then I noticed there was some actual discoloration.

When in doubt, throw it out. If it doesn't smell like when you first used it, then there is probably something going on with it whether it is rancid, moldy, etc.

And yes, the best way to keep specialty flours if you have the space is in your fridge or freeze in an airtight container.

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The flour has turned bad when it starts to have a slight minty odor. It's developing a fungus.

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I believe that flour wouldn't go rancid nor spoiled for just two weeks. Spoiled flour smell like paint tho, and it taste quite bitter

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It's easy for me to tell how it smells. Trust me it smells like pigeon. I had an craft made up of flour. Once that was rotten, it started to smell. When ever I entered the room, I felt like a pigeon had been there already, but then I discovered that craft stank so bad, I had to take it out since it was the source.

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