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I've been making garlic butter for years, storing it for months at a time. When I read that garlic-in-oil can grow dangerous amounts of botulinum toxins after similar lengths of time, I wondered how safe garlic butter is and why.

Evidently, the safety warnings specifically target storage in oil. I couldn't find a satisfactory explanation for butter not being mentioned with a preliminary search. The first Google result turns up a grossly unhelpful Yahoo! Answers page whose sources do not mention butter at all.

To the point: is garlic butter safer than garlic-in-oil, and why? Is butter not also an anaerobic environment, so that the same precautions should apply as with oil?

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Are you storing it in the refrigerator? –  Aaronut Nov 14 '13 at 13:02
Yes, naturally. However, I never minded keeping it out for up to about 4 hours to spread it more easily or use it in longer cooking sessions. –  FvD Nov 15 '13 at 7:02
Garlic oil is also much safer in the refrigerator (though still not great for long term storage). The really strong warnings are for the people trying to bottle it and keep it on the shelf. –  Jefromi Nov 15 '13 at 15:15
A common recommendation from health authorities seems to be 1 week max in the refrigerator for garlic-in-oil. It'd be good to know if butter is safer for chemical reasons, or if I just got lucky. –  FvD Nov 18 '13 at 3:38
This question is close to home. Not finding anything online myself, I just sent an email to a distinguished doctor of Food Science, and will reply (if he does not himself) with any forthcoming information. –  ipso Dec 12 '13 at 22:03
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3 Answers

Garlic butter should be safer because you make it by chopping up garlic and cooking it in butter. The cooking reduces the water content in the garlic to low enough levels that botulism bacteria should no longer an issue.

The garlic in oil issue is that at the water content and pH of garlic, oil blocks the oxygen, allowing the anaerobic bacteria to thrive. But if you change either the water content, by cooking, or the pH, by pickling, then the bacteria can't grow.

Of course, either cooking or pickling will change the taste of the garlic, but both are delicious, so it's fine. :)

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Not only does butter contain more water than oil, this well-researched answer states that botulinum spores would grow on dried garlic immersed in oil. Butter would be more dangerous if water content was the deciding factor. Also, the garlic butter recipes I know don't involve cooking. –  FvD Feb 26 at 2:41
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Unlike oil, butter isn't pure fat. Typically, it's around 80% fat in an emulsion with roughly 20% water and dissolved milk solids. So, no, it's not a truly anaerobic environment. If it were melted or clarified, it may be a different story. Furthermore, butter's crystaline structure -- at room temperature and below -- is bound to be aerated to some degree or another.

Also unlike oil, which is usually stored at room temperature, butter is usually stored at or below 40 degrees F, which retards bacterial reproduction of any kind. The botulism bacteria itself isn't inherently dangerous. It's pretty common in soil and also, therefore, in agricultural products, especially root crops like onions and garlic. When the bacteria reproduces under anaerobic conditions, however, there is a toxic chemical by-product of that specific process. Since low temperatures retard bacterial reproduction, they also reduce the risk that the toxin will be produced.

Realistically, the risks of garlic-in-oil preparations are probably mostly over-stated, but it can be a complex issue, and the consequences of botulism poisoning are too grave to take any chances.

That said, if you're making garlic butter with fresh garlic and storing it anywhere but the freezer, "months at a time" seems like too long, from a quality perspective if not a food-safety one.

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The water and dissolved milk solids may make it not a pure fat, but they don't make it a non-low oxygen environment. Storing garlic in oil in the refrigerator is also discouraged because some of the botulism strains are active below 4 C, and since most refrigerators cycle up and down around their target temperature, growth is possible. While the risks may be exaggerated for garlic in any fat, you have not distinguished the butter case in any meaningful way. –  SAJ14SAJ Nov 14 '13 at 21:58
1) I'm not sure the structure of butter can be called crystalline, even if it solidifies at room temp. Even then, this link suggests that oxygen levels in processed fats like butter would be kept low to increase its shelf life. Water would not inhibit bacterial growth, so I don't see how this would explain a difference to other oils. 2) From a personal taste perspective, the garlic butter becomes more potent over the weeks (as the aroma diffuses into the fat, presumably). Quality doesn't seem to suffer until the butter turns rancid. –  FvD Nov 15 '13 at 7:44
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3 days if not refrigerated. 14 days in a fridge. Freezing is not recommended.

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Is there some documentation or reasoning for this? –  SAJ14SAJ Nov 28 '13 at 23:50
My husband is head chef at Veritas and I asked him. He's been a chef for nearly 30 years. –  Amanda Nov 29 '13 at 0:02
And can he provide you with some documentation or reasoning? This is a safety question; making assertions without backing is not really a good thing. –  SAJ14SAJ Nov 29 '13 at 0:03
ehow.com/how_8289511_make-garlic-butter-compound.html if you read it at the end it says it has shelf life of one week. You can freeze if you wish but fresh is always tastier –  Amanda Nov 29 '13 at 0:12
Why is it different from oil? (And I know you meant well, but ehow isn't really the most trustworthy source - that article was written by someone who didn't cite sources, and doesn't have a culinary or food safety background, so she might well have just picked the amount of time it seemed to stay good for.) –  Jefromi Nov 29 '13 at 5:05
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