The query above comes from the former editor of a New Mexico magazine that ran a story about a garlic oil made by the Valley Garlic Co., a small firm in Placitas, N.M., that makes garlic-infused oil and distributes it to local restaurants and markets. She says, “I've used the oil quite a bit and I think it has great flavor. Also, it hasn't killed me.”
Here is the e-mail message she forwarded to me:
“We produce [brand name deleted] Cold Pressed and Roasted Garlic Juice. … The article about olive oil mixed with garlic juice ([the] article calls it garlic oil) is not quite right and can be [an] extremely dangerous mixture. Oil and garlic juice can develop, under [the] right circumstances a botulism [sic]. It is against the law in most states to have oil and garlic juice premixed and on tables in restaurants, etc. Actually, garlic oil is not edible and is created through steam distillation of garlic juice and is so caustic it must be handled with special gloves. If it touches your skin you can lose some skin and must wash immediately. It cannot be ingested.”
Hoo, boy! There are enough distortions and half-truths in there to fuel an entire election campaign. First of all, the e-mailer—whose company sells pressed garlic juice—gets his oils mixed up. When the magazine story referred to “garlic oil,” it was referring to olive oil that has been infused with garlic: garlic-flavored olive oil. It was not referring to the intrinsic essential oil that gives garlic its unique flavor and aroma. In its pure form, that essential oil will indeed irritate the skin, although “losing some skin” is more than a trifle melodramatic. True, a teaspoon of one of its main ingredients, allyl trisulfide, would kill half the people who swallowed it, but you could never eat enough garlic to come within miles of that much, nor would anyone come within miles of you if you did.
It's important, then, that the world distinguish clearly between garlic-infused oil and garlic's inherent essential oil, which truly deserves the name “garlic oil” and is never ingested in pure form. Lest their customers be frightened off by this e-mailer or other alarmists, I suggest Valley Garlic re-label its “Garlic Oil” bottles “Garlic-Infused Olive Oil.”
When chemically pure garlic oil is required for non-food purposes (it is an effective antibacterial, antifungal and insecticide) it is obtained, as are most plant essential oils, by steam distillation, in which the crushed plant material (not the juice) is exposed to hot steam. The steam vaporizes the oils and the mixed vapors are condensed, whereupon the water and the oil settle out as separate layers.
So is garlic-infused olive or other vegetable oil dangerous? It depends on how you make it. If you add garlic cloves willy-nilly, unpeeled or peeled, whole or minced, to oil and let it stand for weeks at room temperature, yes, you're flirting with botulism.
The lethal Clostridium botulinum bacterium lives in the soil and in stream and lake sediments among other places. It cannot live in extreme dryness or in air, but will thrive in a moist, airless (anaerobic) environment. And exactly those conditions can exist on the surface of a moist garlic clove smothered in oil.
C. botulinum bacteria can be killed by heating for 10 minutes at a temperature above 175° F, although their spores can survive up to several minutes at 250° F. But even killing both the bacteria and the spores may be too little too late because it's not the bacteria themselves that are the villains; it's a neurotoxin they manufacture as they multiply. Botulinum toxin is one of the most powerful poisons known, and we can't depend on the heat of cooking to destroy it. The symptoms it causes were named botulism after a number of people died in Germany in the late 18th century after eating contaminated sausage; the Latin word for sausage is botulus.
Botulism is rare, with only 10 to 30 outbreaks per year in the United States, so there is hardly a galloping botulin plague going on. But a head of garlic just might have some C. botulinum bacteria and spores lurking under its skin, where they had lain protected from air until finding themselves in an airless medium, such as when buried in a sea of oil. There, they can become active and launch a reproductive orgy.
The Safe Solution
Commercial garlic-infused-oil products are generally safe because they contain vinegar, and the bacteria cannot survive in acidic (below pH 4.6) media, THOUGH THE SPORES MAY BE ABLE TO. If you buy some, make sure there is an acidic ingredient listed on the label and keep the product refrigerated whether it tells you to or not.
I spoke with Berry Hickman of Valley Garlic Company and learned that she avoids having to add the acidity and flavor of vinegar by first infusing her olive oil with chopped garlic and then thoroughly filtering off and discarding all the garlic and its juices, which is where the bacteria can grow and generate their poison. The bacteria cannot reproduce in the moisture-free oil itself.
Hickman assured me Valley's technique has earned the approval of inspectors from The New Mexico Department of Agriculture and the local health department. That's good enough for me.
Robert L. Wolke (www.professorscience.com) is professor emeritus of chemistry at the University of Pittsburgh and the author of What Einstein Told His Cook: Kitchen Science Explained. This column was originally published in The Washington Post. f