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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?

FvD
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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 07:02
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    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. – Cascabel Nov 15 '13 at 15:15
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    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 03:38
  • 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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    I'm wondering if it has to do with the fact that butter goes bad much quicker than oil does. You could conceivably have oil for a few months and it would still be ok, but butter would go rancid, so maybe garlic butter will go rancid before it's likely to have any botulism in it? – Daniel Chui Feb 20 '14 at 20:53
  • More people are likely to place butter in fridge than oil, so it is "more safe" – TFD Apr 21 '14 at 22:39
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    Botulism is still quite rare in most countries. Many people are ignorant of it, yet there are very few documented cases of it – TFD Apr 21 '14 at 22:40
  • Fresh vs granulated ---Both seem to be naturally able to contaminate the mixture, oil or butter. I decided to make a "quick and dirty" garlic spread using granulated garlic. Within a week, the garlic caused the combination to turn green. From now on, I'll just make it fresh, or make a batch and freeze small packs. Why take the chance with butter when you can freeze it? – DaaBoss Feb 25 '15 at 02:03

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I suspected that @FuzzyChef's answer was essentially correct, but I felt that the question was not conclusively answered without sources, so I ended up never accepting an answer. Thankfully, Linda Harris published this very comprehensive summary (which I recommend you to read if you are a fan of garlic), from which these parts stand out:

Garlic is a low-acid vegetable. The pH of a clove of garlic typically ranges from 5.3 to 6.3.
[...]
Adding wine or vinegar to garlic provides an acidic environment (less than pH 4.6) so that Clostridium botulinum cannot grow.

A quick Google search reveals that butter has a pH of 6.1 - 6.4, so there is indeed no reason to believe that garlic butter is safer than garlic in oil.

As the summary says that garlic in oil is safe for up to 4 days in the refrigerator, it should be safe to assume that the same would hold for garlic butter.

Most interestingly, however, the document explains a method to acidify garlic for long-term storage in oil, based on research that was published a year after this question was originally posted. The method should be just as valid for garlic butter. In short:

  1. Prepare 3 parts of 3% citric acid solution (about 15 g citric acid / 500 ml water) per part of garlic to be acidified (and don't change this ratio, obviously)

  2. Coarsely chop the garlic into pieces no longer than 6 mm (1/4 inch) in any direction

  3. Put the garlic in the solution, mix, cover and let soak for 24 h at room temperature, then drain/sieve.

This acidified garlic is safe to use in oil (and presumably butter), according to science. Enjoy!

FvD
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There's no reason to believe it's safer.

Garlic in oil is "unsafe" by FDA standards. Which means that roughly one in 100,000 bottles of homemade garlic oil kills someone. Before reading about the botulism risk, my friends and I used to make garlic oil at home and hand it out; I'd say we distributed probably 100 bottles, some of which stayed on the shelf for years before being used. In that time, nobody got sick from it (most bottles went to friends, so we'd have heard).

So the fact that your garlic butter hasn't killed anyone yet just means that you're playing the odds. Chances are, unless you get really sloppy, you could go on making garlic butter for the rest of your life and never get botulism poisoning. But not everyone is comfortable with that risk.

EDITED PER BELOW: You can improve your odds of avoiding botulism by straining the oil/butter through cheesecloth (to eliminate solids which would hide spores), and heat-treating it to 160F or more for 45 minutes. This will not eliminate all risk of botulism, but will improve your odds.

FuzzyChef
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    I agree that unless we find a reason why garlic butter isn't mentioned alongside garlic-in-oil in those health warnings, it should be assumed that both are equally dangerous. However, I can't see how that would imply better food safety when straining butter through a cheesecloth. The environment would still be anaerobic, and the spores are heat resistant. Is there any source for this? – FvD May 07 '14 at 13:44
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    The straining through cheesecloth is to eliminate hydrous solids which could protect spores from the heat-treatment.

    However, you are correct that my recommentations for heat treatment duration are inadequate. Edited entry.

     – FuzzyChef Aug 11 '14 at 22:29
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Clostridium botulinum grows best around body temperature.

Typically, butter — as opposed to oil — is stored in a cool place which significantly reduces bacteria growth in general, including the growth of Clostridium botulinum. The CDC in 2010 specifically recommended cooling as a means to prevent Botulism.

Botulism is rare to begin with (the CDC page gives a number of 110 annual cases in the U.S. of which only 25% are food-born.1).

I'd be totally cool about food in the fridge ;-).

As an aside, the whole issue is moot (for adults) if the food is cooked for a few minutes before consumption. Botulism in adults is not an infection (our acidic stomach sees to that) but caused by the toxin already present in the food. The toxin is destroyed at boiling temperature. You can cook with your garlic oil no matter how old, just don't put it in the salad.

1 It is perhaps worthwhile to put the numbers in perspective. In the US, about 5,000 people each year die from choking, as opposed to three or so from Botulism. The best advice is "we don't care how you store your garlic as long as you chew it properly" ;-).

Peter - Reinstate Monica
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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.

Pete
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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
  • 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 07:44