What you see: Garlic 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. If homemade and never refrigerated, or refrigerated for more than four days, toss it.
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, garlicy 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, as in, within an hour or less. 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 is finicky
Botulism’s only silver lining is that it’s finicky. The bacteria needs non-acidic, oxygen-free conditions to thrive. So, while clostridium botulinum spores are part of our environment and undoubtably in some of our food, they don’t hurt us because as long as oxygen is 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 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 extra attention because of its botulism 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, it's foods designed to be eaten at room temperature that are assembled in low-oxygen conditions that 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. This is hard to do at home, but the University of California offers some guidelines in this report. For most of us though, the best thing to do is to just enjoy your garlic and oil cooked, freshly mixed, or purchased from the store.
Botulism poisoning is very rare
Before you swear off garlic forever, keep in mind that botulism poisoning is extremely rare. In 2016, for example, the Centers for Disease Control counted only 29 confirmed cases of food-borne botulism across the United States. Nineteen of those cases were connected to illicit alcohol production in a Mississippi prison. Most of the remaining cases involved home canning.
But the potentially life-altering consequences of botulism poisoning 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.
Elizabeth Andress, PhD. Professor, Foods and Nutrition and Extension Food Safety Specialist. College of Family and Consumer Sciences, University of Georgia. Project Director, National Center for Home Food Preservation.
Foodbourne Botulism - Food Safety Authority of Ireland
Botulism - Symptoms - Centers for Disease Control
Botulism Fact Sheet - World Health Organization
Safe Homemade Flavored and Infused Oils - University of Maine
Garlic - Safe Methods to Store, Preserve and Enjoy - University of California, Davis
Garlic Kept in Olive Oil Can Turn Deadly - Baltimore Sun
Evaluation and Definition of Potentially Hazardous Foods - FDA
How to Dry Foods. Deanna Delong. Penguin Publishing. 2006. p. 85
Flavored Vinegars and Oils - Colorado State University Extension
Food Safety & Preservation - Herbs and Vegetables in Oil - Oregon State University Extension Service Garlic: Safe Methods to Store, Preserve and Enjoy. University of California - Agriculture and Natural Resources. Linda J. Harris. Specialist in cooperative extension, microbial food safety. Department of Food Science and Technology. University of California - Davis.
Current Food Safety Issues of Home-prepared Vegetables and Herbs Stored in Oil. Food Protection Trends, Vol. 31, No. 6, Pages 336–342. B. A. Nummer, D. W. Schaffner, A. M. Fraser and E. L. Andress.
How Not to Die of Botulism. The Atlantic.
National Botulism Surveillance Summary 2016 - CDC.
Garlic-in-oil associated botulism: episode leads to product modification. American Journal of Public Health. 1990 November; 80(11): 1372–1373. D. L. Morse, L. K. Pickard, J. J. Guzewich, B. D. Devine, and M. Shayegani.
You think your favorite TV crime drama is scary? Check out this investigator's report:
"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