Garlic-in-oil mixtures, sold in jars in grocery stores, are popular with the busy cook. But making your own garlic, herbs or hot peppers-in-oil mixtures at home can be hazardous to your health, because bacteria that cause botulism can grow, according to Carolyn Raab, food and nutrition specialist with the Oregon State University Extension Service.
Commercial garlic-in-oil mixtures are acidified to prevent bacterial growth. Most of these store-bought products can be stored safely at room temperature. Look for storage instructions on the label.
Unfortunately, do-it-yourself acidification of homemade herb or vegetables-in-oil mixtures is risky, because not enough research has been conducted to know how much acid is needed to prevent bacterial growth.
These low-acid foods can be a source of ‘Clostridium botulinum’ bacteria, according to Raab.

Clostridium botulinum produces a toxin that causes botulism, a cause of fatal food poisoning. Because these bacteria are found naturally in soil, water and air, they could be found in any low-acid food and begin to grow and produce toxin when the conditions are right. That’s why it is crucial to keep food safety in mind when storing your own low-acid vegetables such as garlic, mushrooms and chili peppers or herbs in oil.
Raab recommends taking the following steps to ensure food safety when making and using your own homemade herb, vegetables and garlic-in-oil mixtures:
Refrigerate fresh vegetables or garlic-in-oil mixtures, and don’t keep them any longer than three weeks. After three weeks of refrigeration, botulinal toxin could have formed. Remove the vegetables after flavoring the oil and the bacteria will not have a food source for growth.
Use dried vegetables, garlic or herbs to flavor oil. These do not contain enough water to foster bacterial growth. Dried vegetables, garlic or herbs-in-oil mixtures can be stored safely at room temperature. Refrigeration may delay rancidity.
Tomatoes-in-oil mixtures are safe, as tomatoes are high in acid and will not foster botulism-causing bacterial growth. Refrigeration may delay rancidity.
Don’t use vegetables-in-oil mixtures that show any signs of spoilage such as bubbling or cloudiness.
Home canners in Oregon can get answers to questions by calling the OSU Extension Food Safety/Preservation Hotline from July 18 to Oct. 14 at 1-800-354-7319, Monday through Friday from 9 a.m. to 4 p.m. except holidays. OSU Extension Family Food Education volunteers and Extension faculty and staff will run the hotline.