From S.J., 28 November 2011, garlic confit: is it safe?
Q: With the current popularity of “Garlic Confit”; How wonderful it is, if it doesn’t kill you. I am curious…Would the addidtion of salt (say 1 teaspoon per cup of oil) create enough of an acidic environment to make it safe or store longer? I have also seen mention that adding ascorbic acid will prevent spore growth, but cannot find what quantity to add. Any assistance will be greatly appreciated.
A: Hi and thanks for your question. Garlic confit is pretty excellent. I use it far more than I use raw garlic, since it has the depth of flavor that garlic enjoys (and a little nuttiness), but not the aggressive bite that can take over a dish.
A couple of years back, I provided the method for making garlic confit, and noted that you shouldn’t make more than you can use in two weeks at a time and refrigerate your product, to reduce the risk of botulism. The risk exists because C. botulinum spores, omnipresent in the environment, can produce a potent neurotoxin if the spores germinate. Germination takes place under anaerobic (airless) conditions, so garlic confit – in which garlic cloves poach in oil and then are stored in the poaching oil – is a friendly environment. In most cases, botulism is caused by the toxins from type A and B spores, which give off gases as they produce toxins, and are the reason you’ve been told not to eat any canned food that comes out of a bulging can or jar. There are other types of spores that do not give off gases or funny smells, but their toxins are destroyed at lower temperatures and really are only an issue if you don’t cook the food at an adequate temperature before eating it.
C. botulinum spore growth is inhibited at a pH of 4.6 or under, which is why high-acid foods like tomatoes and most fruits are good bets for home canning – they are acidic enough not to pose a risk. The spores survive the conventional boiling point of water (212F/100C), so pressure canning, which allows the product to reach a temperature of 251F/121C at 15 psi, is necessary to eliminate the risk. This is why low-acid foods like garlic, green beans, and most other vegetables must be pressure canned to be safe, unless they’re pickled. In addition, boiling (or technically cooking at 180F/82C) for at least ten minutes destroys the toxin.
Enough with the science. What does all this mean for you? In a nutshell, don’t freak out. The risk of botulism from garlic confit is actually very low as long as you follow standard safe food preparation and storage practices. If you cool your product immediately and then store it in your refrigerator (as long as your refrigerator is adequately cold), you will limit your risk substantially, since growth of the type A spores, which produce the most potent and dangerous toxin, is inhibited under 50F/10C. Growth of the other types is inhibited under 38F/4C; their slow growth is the reason I recommend not making too much and using it within two weeks. Under no circumstances should you store your product above refrigeration temperatures.
You asked about using salt or ascorbic acid (Vitamin C) to create an acidic environment to inhibit spore growth. First, using sodium chloride does not create an acidic environment, as salt solution is pH neutral. Second, I doubt you can reliably achieve a low enough pH – using any kind of acid, ascorbic or otherwise – in the home environment. You need to acidify the garlic before cooking by soaking in an acidic solution to impregnate the garlic, and then ensure with a pH meter that you have lowered the pH to 4.6 or less. It’s not feasible for most people. I do think it’s possible to reduce the number of existing C. botulinum spores on the surface of the garlic by washing the peeled cloves very well, and possibly to reduce them further by soaking them for a few hours in a low pH solution before rinsing in water and cooking, but I wouldn’t count on it.
So go ahead and make your garlic confit, in relatively small amounts. Cool it immediately by transferring it to a container and setting that container in an ice bath; stir until the mixture is cool. Store it in a covered, shallow container in the coldest part of your refrigerator, use it frequently, and finish it within a week or two. I’ll emphasize again what I said in my earlier post – don’t every try to store the garlic confit (or either component) in an anaerobic environment, such as by vacuum sealing or canning other than pressure canning at 15 psi. If you want to read more on the subject, Health Canada has addressed it in a nutshellhere, and the National Center for Home Food Preparation at the University of Georgia has published this great primer on safe garlic preparation.
Update: This public health briefing describes the last known incident of commercial garlic-in-oil botulism, in 1989. It involved the use of commercially prepared chopped garlic in oil (not confit); the garlic had been canned in oil and stored at room temperature. Because of this episode, the FDA mandated steps to reduce the risk of botulism in garlic products.