Caution: Don’t Can in Oil
Posted: July 2, 2012
Storing vegetables or herbs in oil is not recommended because both the herbs and the oil provide conditions that can support the growth of Clostridium botulinum bacteria. The heat stable spores of this bacteria can produce deadly amounts of toxin in environments that are free of oxygen, at room temperature, and low in acid.
The likelihood of onion, garlic, peppers, or herbs having some bacteria and/or spores present even after washing is great. When these are placed in oil, the oil surrounds the spores preventing any air (oxygen) from reaching the spores fostering the conditions necessary for the production of botulinum toxin.
Prepare only the amount of flavored oil, pesto or marinated vegetable that you can use within three days. Otherwise, discard. If you plan to keep them longer, freeze them.
The only exceptions to the above are scientifically tested recipes. The USDA Complete Guide to Home Canning, includes three recipes that have oil in the ingredient list: marinated peppers, marinated whole mushrooms, and pickled three-bean salad. Each of these recipes includes added acid ingredients (lemon juice, vinegar) as well as preparation steps to ensure adequate acidity of the vegetable. There is a small amount of oil in each recipe and sufficient amount of acid. These recipes have been scientifically research tested for safety. In the absence of a scientifically research tested recipe, it is safest to freeze a product.
These recipes are available at the Penn State Extension Food Preservation website.