Why garlic and herb oil infusions can be dangerous

What you see: Garlic cloves deliciously infusing in oil.
What it is: A potential harborer of botulism.
Eat or toss: This depends entirely on the circumstances. If purchased from the store, it had to meet regulations so should be fine. Homemade garlic-in-oil infusions need to follow special, validated recipes to be shelf stable. If they don’t they should be refrigerated and used within several days.

Poorly handled garlic-infused oil can be unsafe to eat

It sounds so appealing to drop some freshly chopped garlic in olive oil, let things infuse for a while, and then dip your bread in the olive-y, garlicky goodness.

But, please, drop the bread and step away from the garlic oil. Or, if you’re going to mix garlic and oil, skip the infusing step and use the concoction right away. Unfortunately, this delicious-sounding combination is a recipe for botulism.

Botulism is invisible and terrifying

Botulism is a potentially deadly paralytic disease caused by a toxin produced by a particular food-inhabiting bacteria. The bacteria and its toxin are especially scary because they don’t affect flavor, so if you didn’t know to be afraid of garlic-infused oil, you might not know something was wrong until your vision started to blur and you had trouble swallowing.

But botulism-producing bacteria are finicky

The only silver lining of the bacteria that make botulism toxins is that they’re finicky. They needs non-acidic, oxygen-free conditions to thrive. So, while clostridium botulinum spores are part of our environment and undoubtably hanging out on some of our food, they don’t hurt us because as long as oxygen and/or acid are present, they’re on lockdown and aren’t producing their trademark toxins. That is, of course, until you invite them to do so by dropping your garlic in some oil and leaving it at room temperature for more than a couple hours. Storing it in the fridge will slow the bacteria’s growth, but even then, after a few days, you should say goodbye.

Garlic in oil creates ideal botulism conditions

Despite its potency, garlic is a low-acid food, which clostridium botulinum thinks is great. Garlic also contains water, another plus in the bacteria’s book. Pour some oil over it and boom, you’ve also blocked all the oxygen in the air. Keep it at room temperature and you’ve created just the environment for clostridium botulinum to kick back, break free from its protective spores, and proliferate like mad.

Cooked garlic requires care as well

While garlic in oil is particularly worrisome given its odds of being stored at room temperature, garlic in any dish generally requires a little extra attention because of its botulism favoring tendencies. Unfortunately, heat doesn’t kill the spores, so you can’t roast or sauté the botulism risk to oblivion. But, heat does destroy the toxin itself—five minutes or longer at 185 Fahrenheit should do the job, according to the World Health Organization. So, logically, WHO notes, foods designed to be eaten at room temperature that are assembled in low-oxygen conditions are most often the culprits in botulism poisoning.

Commercial processors are required to acidify to cut botulism risk

Commercial food producers use a process called acidification to ensure that their garlic-in-oil products do not create a friendly incubator for bacteria. Acid prevents the spores from germinating. Acidification is hard to do at home, but it’s possible if you want to try.

How to make a garlic or herb infusion at home

Like garlic, fresh herbs are low-acid foods and can carry spores of the bacteria that cause botulism. If you want to make a garlic or herb infusion at home you have two options:

• If you just want to whip up–and consume–something quickly, normal food handling rules apply. Just keep it in the refrigerator when you’re not using it and eat it within several days.
• If you want to make a shelf stable product, then you’ll need to follow precise steps to acidify the garlic or herbs. The University of Georgia offers a recipe, which uses a citric acid solution. It’s been lab tested for safety so you’ll want to follow it exactly.

Botulism poisoning is very rare

Before you swear off garlic forever, keep in mind that botulism poisoning is extremely rare. In 2018, for example, the Centers for Disease Control counted only 18 cases of food-borne botulism across the United States, as reported by health departments. The cases involved a variety of homemade foods, but none were traced to oil infusions.

But the potentially life-altering consequences of botulism illness merit our diligence. While it’s rare to hear of a case where someone was harmed by a garlic-in-oil concoction, Elizabeth Andress, project director at the National Center for Home Food Preservation, notes that the botulism-prevention requirements for food processing were instituted after a string of incidents in the 1980s. In 1989, the Food and Drug Administration required that all commercial garlic-in-oil products go through an acidification process.

For some less frightening articles about garlic, check out our Garlic Index!

You think your favorite TV crime drama is scary? Check out this investigator’s report on a case of confirmed botulism:

“The garlic bread was prepared by mixing two teaspoons of garlic-in-oil with warm margarine and spreading in on pieces of pita bread. The bread was wrapped in aluminum foil and heated in an oven (300 degrees Fahrenheit) for 20 minutes prior to serving. The implicated chopped garlic in olive oil product was processed sometime between 1985 and September 1987.”

~From Garlic-in-OIl Associated Botulism: Episode Leads to Product Modification

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This post was first published June 4, 2018, and updated Jan. 19, 2023.