botulism from garlic in olive oil?
I have heard that you can create botulism from putting garlic in olive oil. Is that just making garlic infused oil? Or does the same risk appear if I want to use it in a soup?
This is the recipe
Roasted Garlic Soup with Parmesan
26 cloves roasted garlic (2-3 heads)
2 tablespoons olive oil
2 tablespoons butter
2 ¼ cups sliced onions
1 ½ teaspoons chopped fresh thyme
18 cloves garlic , peeled
3 ½ cups chicken stock or 3 ½ cups vegetable stock
½ cup whipping cream
½ cup finely grated parmesan cheese (about 2 ounces)
4 lemon wedges
As you can see both garlic and olive oil are in this recipe. Can this create botulism?
Is it safe to put these two things together in the soup?
Botulism is destroyed by 10 minutes of boiling so when you make your soup, you will destroy any botulism spores.
Garlic has a tendency to have botulism spores on the surface of the bulbs. When the bulbs are put in a "Low oxygen" environment like olive oil, the spores can multiply. Using a sterile jar and heating the olive oil up to past 250 degrees for a few minutes and washing the garlic bulbs lowers the chances of botulism surviving but does not guarantee it.
The only way to guarantee it is too cook the garlic at above 250 degrees for a few minutes. You could cook it in a pressure cooker or stew the bulbs in hot olive oil at 250 degrees or higher. It would be safe then.
The same for making your own truffle oil. The truffles would need to be cooked in olive oil for a few minutes.
re: Hank Hanover
Boiling for 10 minutes destroys the toxin, but it doesn't kill the spores. Things like jam are safe to can in a boiling water bath not because the spores die, but because they're acidic and that inhibits bacterial growth. That said, I've never been able to find any reported cases of illness from people who cooked garlic thoroughly in oil, strained the oil, and refrigerated it. I do that myself.
re: Hank Hanover
The supermarket jarred garlic in water is not the same as garlic in oil. The botulinum bacteria are anaerobic, and will thrive in the completely anoxic olive oil. Aside from any dissolved oxygen in the water, a little bit of additional acid will lower the pH to the point where botulinum can't survive.
It is actually the other way around. Heat destroys the spores, but will not denature the toxin.
So in the above recipe example, if the soup was put together and allowed to sit around for several hours before cooking, there is a significant likelihood of getting food poisoning, because the spores are able to colonise and produce toxin.
If the soup is heated immediately, the spores are killed off before they have a chance of growing.
Botulism bacteria are present on many foods and throughout our environment. The problem is when they multiply -- which they do in an oxygen-free environment when the acidity is not too high and the temperature is not too low. This is the reason that safe home canning requires sticking to tested recipes and following the instructions about sterilization and processing for a given time.
Garlic sitting in oil, unrefrigerated, is an environment in which botulism bacteria can grow to dangerous levels (producing enough of the toxin to sicken or kill) within a day or two. Infusing oil with garlic poses little risk if you immediately use the oil for cooking, or drizzling. But it cannot be stored unrefrigerated, because the heat level used for infusion is not enough to kill Botulinum bacteria. [Which would be killed by roasting the garlic as the original post's recipe calls for; garlic is typically roasted for about 45 minutes at 400F. It's a very different flavor than oil infused with raw garlic, though.]
Commercial production of garlic-infused oil presumably involves steps that eliminate the bacteria, so that product can be stored outside the fridge.
The risk for botulism exists for other herb-infused oils; a lot of the recipes I've seen don't sufficiently emphasize those risks or the steps to minimize them.