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My girlfriend and I are thinking of preparing some flavored oils for Christmas presents this year (don't tell anyone!). We've read online that fresh garlic presents a health hazard when stored at room temperature, because the low-acidity, oxygen-free environment is perfect for the botulism-causing spore to develop.

In order to avoid this, we've used dried, minced garlic (bought at the store). However, I haven't found any substantial evidence that this mixture is safe for storage at room-temperature. One site mentioned that the lack of water in the garlic removes the "food" for the spore, and therefore the risk.

Do you know if dried garlic (or any other easily available garlic type) can be stored for longer periods at room temperature?

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Not that I doubt my own answer, but typically you should wait at least a few hours (most of us wait a day or two) before accepting an answer, just in case somebody more knowledgeable comes along. I know that the system kind of prods you into it, but in practice it's best to give the community a chance to weigh in before making up your mind. Just wanted to let you know that for future reference. Welcome to the site by the way! :) –  Aaronut Nov 15 '10 at 20:52
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(Somewhat off-topic:) A few years ago, I tried to make garlic oil by just dumping fresh garlic into oil, and had the cloves turn bright blue after a few days. I called the Dutch Centre for Nutrition (a government agency that informs citizens on nutritional issues) and they didn't have any idea what it could be. I now realize it may have been botulism... –  Erik P. Nov 15 '10 at 22:11
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@Erik: Is botulism blue? I thought it was basically invisible, odourless and tasteless, which is part of the reason it's so dangerous. If your garlic turned blue, that's more likely to be a chemical reaction - probably with copper (raw garlic contains a lot of sulfur). –  Aaronut Nov 16 '10 at 2:08
    
@Aaronut: you may well be right. It was just the idea of botulism apparently not being uncommon on garlic (and your answer indicating that it might grow in oil) that inspired the idea. –  Erik P. Nov 16 '10 at 15:24
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@ErikP., garlic pretty regularly turns blue depending on the strain when it's put into an acidic environment. see extension.psu.edu/food/preservation/news/2012/garlic-turns-blue –  dax Aug 29 '13 at 14:08

6 Answers 6

up vote 12 down vote accepted

The most common data point seems to be that any moisture level below 35% will inhibit growth of the C. Botulinum spores that cause botulism. It's hard to point to true scientific sources because they tend to be protected, but if you spend a few minutes on Google (try this query) you'll see that it is in fact confirmed in several of the scientific journals.

I seem to be seeing snippets of references (which I can't view the full text of) that suggest possible growth at moisture levels as low as 16%, but most garlic flakes have 6% moisture or lower, which is way too low for botulism.

If you are seriously concerned - perhaps you live in a very humid climate and don't have air conditioning - then toss a desiccant into the container to be sure that the moisture level stays down. The most popular are those little packets of silica gel (don't open them!), but there are many more - see Wikipedia's list of desiccants.

Honestly though, chances are your flaked garlic is already free of C. Botulinum spores after the dehydrating process, and nothing's going to grow no matter how you store the dried stuff. The above paragraph is only included for the hyper-paranoid. Powdered/flaked garlic is safe to store at room temperature.

If you're actually storing this garlic in the oil (it's not entirely clear from your question) then that's another story, and theoretically you're making it possible for the spores to grow again. So it comes down to a question of whether or not the garlic flakes are already clean. That's extremely likely to be the case, but not a sure thing, and personally, I don't know if I'd chance it; best to follow the same precautions as those for fresh garlic and soak them in vinegar for 24 hours to kill any spores (although you might as well use fresh garlic in this case).

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Thanks Aaronut! Yes, I'm actually thinking of putting the garlic (not just, also some other dried spices, etc.) into oil, in order to give it flavor. I'm not a chemistry expert, but based on your answer I guess that oil does not count as a source of "moisture", and the mixture should be safe for use... –  Miguelón Nov 15 '10 at 20:49
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@Miguelón: I think you may have misinterpreted my answer; my last paragraph should make it clear that oil is moisture and can promote botulism, if there's any on your garlic flakes to begin with. That's a pretty big "if", but be aware that there may still be some risk with what you're planning to do. –  Aaronut Nov 15 '10 at 20:54
    
Thanks for the precission... better safe than sorry, as they say :) –  Miguelón Nov 15 '10 at 21:03
    
You may want to cite this paper from the American Journal of Public Health (free access): Garlic-in-oil associated botulism: episode leads to product modification. –  nico Aug 30 '11 at 21:09
    
@nico: I'm not quite sure how that relates to dried garlic. Does that paper state somewhere that spores can survive dehydration? –  Aaronut Aug 30 '11 at 22:14

I've seen people have a lot more success making infused vinegars than infused oils. None of the oils seem to keep long--even when it's something like rosemary or thyme instead of garlic--maybe there's something about the process that makes them go rancid faster.

Infused vinegars are better, I think. The vinegar is acidic enough to be hard on bacteria, it doesn't go rancid, and infused vinegars are dynamite in salads and such.

That's how I'd go if making infusions as gifts. Well, that or making alcohol infusions like limoncello, which is what I'm doing this year.

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As far as I am aware, The only safe way to store non-acidulated garlic in oil is to do so at 38 degrees F or lower.

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Bad idea....
This is one of the major causes of food poisoning, in homes and in restaurants. And people have no idea, in fact in know people who have a bottle of garlic in oil in the fridge thats been around for a year... They really should throw it out.

My understanding is that the low fridge temperatures don't stop the growth, just slows it down. The Botulinum can still grow. Besides, what happens when they take it out and leave it on the counter for a few hours and put it back in the fridge. And then repeat a few dozen times. If any Water were to get in there...say from a just rinsed spoon...

You cant detect Botulinum by smell, or sight. You just get sick.

Yes it does need moisture, the flakes and oil might be safer than the alternative, but this is a big problem that most people dont realize...

People really should be chopping fresh garlic regularly, or at least throwing out garlic oils every few weeks... ( from the fridge)

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Wow, a LOT of random incorrect information in all these answers! Sorry, but it's true. Each answer is WAY off base!! There is so many rumours about garlic in oil, it's almost like TMZ's enetertainment "reporting" LOL!

Go here. Read the ENTIRE article. The Canadian Food Inspection Agency & Health Services are superior in their information & food safety rules. They're awesome! It explains everything about the spore that releases a toxin (let's call it "spore poop")... the more spores, the more poop. Oxygen does NOT kill spores, it simply prevents them from multiplying. When you remove the air from the equation (you seal the garlic off from the air when you pour oil on it), you start the process if the spore is present. Because it's invisible, odorless, colourless and food with the spore & toxins do not look or smell spoiled or contaminated, there is just no way to know if it is safe -- why risk it?

You can do a garlic in oil, but you CANNOT leave it at room temperature, and you CANNOT keep it safely for more than one week in the fridge. After that point, even kept in the fridge, the toxins can be building up into dangerous levels. Because it's a toxin, it's not something we can build immunity to, like we do with salmonella.

The botulism toxin causes, among other things, paralysis, which is why they use it in those cosmetic procedures (BoTox which is the brand name, it was named such by the inventor of it,7, simply shortened "botulism toxin"). It paralyzes the facial muscles in the wrinkle-zones, so the face doesn't move to create wrinkles in the skin.

The original question was asking about dried garlic -- it is no different than regular fresh garlic. As soon as you seal it off from the air, the spores can multiply & grow. This is also why those vacuum sealers have big warnings not to use their system to preserve garlic. I doubt that dehydrated garlic or garlic salt or garlic powder/dust would have a good enough flavour for an infused oil, for starters. It would make the oil cloudy which would make it look yucky. It's just not worth the hassle to make things like that as gifts because who is going to trust it or be able to use it within a week of it's making? If you really really want to make something, make little herb planters for everyone! If you're on a tight budget, chives are great, they grow like mad from seed & are hard to kill. Or, just get a $2 lotto ticket for each person on your list -- it's safer and you might just get something good back from it. ;)

I hope all of this helps anyone who happens upon this page! :)

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Botulinum forms a spore. Think of the spore like a walnut shell that protects the organism inside. It has been shown to protect the organism from heat and cold. Did you know scientists store live Botulinum in liquid nitrogen? It is one tough bug. Botulinum is anarobic. This means oxygen is an enemy. It goes into spore form when in the presence of oxygen to survive in a domant state.Dried Garlic. Adding oil will provide the anaerobic environment it needs to live. Adding oil to dried garlic will give the Botulinum what it needs to muliply. It will continue to muliply even in your refrigerator. Most people associate Botulinum with mayonnaise but food science has improved our store bought mayo by lowering the pH to below 4.6. Low pH helps control Botulinum. Water content also controls growth. The drier the better. Home made garlic in oil should be treated as a potentially hazardous food in regards to time as a control. 4 hours and it should be tossed.

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Botulinum is a toxin. I gues you are meaning Clostridium botulinum, the bacterium that makes it. –  J.A.I.L. Nov 13 '12 at 8:50

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