Safely Infusing Oils at Home
Oils flavored with garlic or herbs can be a source of the foodborne illness botulism. The mix of the low-acid, produce, potentially containing the bacteria Clostridium botulinum, submersed in oil creates an anaerobic (oxygen free) environment capable of supporting the growth of bacteria spores, which can produce a deadly neurotoxin. The spores cannot survive in an acidic environment. Garlic or herb flavored oils sold commercially have either been acidified or contain specific levels of microbial inhibitors.
Researchers at the University of Idaho developed guidelines for home preservers to safely make infused oil for long term shelf storage. The garlic or herb must be acidified before being are added to the oil. Infused oils prepared without these specific guidelines are not shelf stable. Other methods to infuse oils at home result in products that must be used within 2 to 4 days or refrigerated no more than three months.
Citric acid is used in the researched process. Look for it where canning supplies are sold, in pharmacies, grocery stores and health food stores. Other acids such as lemon juice and vinegar have not been tested and cannot be substituted for the citric acid. Citric acid is not the same as ascorbic acid (vitamin C) which does not have the same ability to acidify the garlic or herbs so should not be used.
Only fresh garlic, basil, rosemary and oregano have been researched. Other ingredients should not be substituted or added.
Acidified garlic for oil infusions
- 2 cups water
- 1 tablespoon granular citric acid
- About 8 ounces garlic bulbs
- Make the 3% citric acid solution. Pour 2 cups warm water into a mixing bowl. Add 1 level tablespoon of granular citric acid and stir gently, dissolving the citric acid completely.
- Separate the garlic bulbs into cloves and peel. Roughly chop the peeled garlic into pieces about 1/4-inch square and no larger.
- Place 2/3 cup chopped garlic into the acid solution and stir gently. Cover and hold at room temperature for 24 hours to allow garlic to become fully acidified.
- After 24 hours, remove the acidified garlic from the solution; drain well, pat dry.
- Add the acidified garlic to your choice of oil and allow its flavor to infuse the oil to taste. Start with 1 part garlic to 10 parts oil, by weight; add more garlic to taste if you wish. Infuse 1 to 10 days.