Infusing olive oil with the tastes and aromas of herbs and spices makes a gourmet pantry item and a great homemade gift. But is it safe to keep your seasoning-infused olive oil at room temperature? Although people have been making infused oils since long before refrigeration, there is a risk of botulism from unrefrigerated infused oils.
What Is Infused Olive Oil?
Infused olive oil is olive oil — usually extra-virgin — that has taken on the flavors of herbs and spices. The usual method of making it is simply to fill a glass jar or bottle with the chosen seasonings, cover them with the oil, and then wait anywhere from one week to a month for the oil to absorb the flavors. Rosemary, chile peppers, and garlic are some of the seasonings commonly used to infuse olive oil.
Why Does Improperly Stored Infused OIl Pose a Botulism Risk?
The olive oil — or any other vegetable oil — is not itself a potential source of botulism. The risk comes from the herbs and/or vegetables used to infuse the olive oil with added flavor. Botulism comes from soils contaminated with Clostridium (C.) botulinum, and anything grown in soil could potentially carry this contamination. The risk is greatest when the ingredient comes from the underground parts of the plant, as is the case with garlic.
How Can I Make Sure My Infused OIl Is Safe to Eat?
Delicious infused olive oil has been made and safely consumed for thousands of years, but there are several steps that will ensure your product is safe to eat. Wash the produce to remove all traces of soil. Use clean glass jars. Sterilize them in boiling water for 15 minutes to be absolutely certain of their cleanliness. Add an acidic ingredient such as lemon juice or vinegar; use 1 tablespoon per cup of oil. Always refrigerate infused olive oil.
How Does Refrigeration Keep Infused Oils Safe?
The cold temperatures of refrigeration retard the growth of microbes. Unlike some other vegetable oils that remain liquid in the refrigerator, olive oil changes to a semi-solid state when it is chilled. It is perfectly safe to return your infused olive oil to a liquid state by letting it sit at room temperature for a few minutes before using it in a recipe, but return it to the refrigerator for storage immediately afterwards. You should discard even refrigerated infused oils after one week, advises Colorado State University Extension, and do so earlier if they discolor, bubble, smell "off" or look cloudy.
Leda Meredith is the author of two books, including "The Locavore's Handbook: The Busy Person's Guide to Eating Local on a Budget." Specializing in wild edible plants, she is also an instructor at the New York Botanical Garden and the Brooklyn Botanic Garden.