Herbal Infused Olive Oil
Infusing olive oil with herbs like basil, rosemary or oregano is easy, but can turn deadly if you don’t follow the proper method of acidifying the herbs before infusing.
Botulism is something of which to be afraid. And unlike most other bacteria, Clostridium Botulinum, the organism that causes the disease, flourishes in an oxygen-free environment. So, while one might think submerging a handful of basil in a bottle of olive oil would be safe precisely because the plant is not exposed to the air, one would be drawing an incorrect conclusion without knowing all the facts. And while there are only 150-200 cases of botulism reported in the US every year, a good number of them are caused from improperly infused herbal oils.
With vinegars, you don’t have to worry about it. You can stuff whatever kind of herb you want in a bottle of vinegar, stick it on the pantry shelf and go on with your life. You can leave the herb in the vinegar indefinitely if you like, and you’ll be just fine. In fact, I just finished a bottle of white wine vinegar that I had infused with fresh tarragon, and it sat on my pantry shelf for over a year.
But, why? And why not the same with olive oil?
Because vinegar is 4-8% acetic acid. And therein lies the answer. Olive oil is not acidic. And bacteria intensely dislikes an acidic environment.
What that means is that you have to make herbs or garlic gloves acidic before submerging them into their olive oil bath, which requires a simple but important pre-step to the infusion process. The Pacific Northwest Extension, a cooperative public education materials source from the University of Idaho, Washington State University and Oregon State University, conducted research on this subject and published a paper in 2011 recommending the process of acidifying herbs for 24 hours in a 3% citric acid solution prior to commencing the infusion process. The amount of acid was different for garlic than it was for three herbs tested, basil, rosemary and oregano, but in either case, it effectively acidified the flavoring agent so that there was no chance of botulinum growth during or post infusion.
Citric acid is no stranger to those who can their own vegetables or make their own jams and jellies. It’s readily available wherever you buy canning supplies or online, and sold as a powder. Just be sure you don’t mistake ascorbic acid for citric acid. They are not the same. Whatever citric acid you buy, be sure it says “Food Grade” or “Suitable for Culinary Use” on the label.
Once you have effectively acidified the herbs you wish to use, you’ll need two pieces of equipment to successfully infuse your oil, and Kitchen Tapestry recommends extra virgin olive oil for this exercise. It marries nicely with herbs like basil. We grow basil hydroponically and use it frequently in our culinary pursuits, but still, having an oil infused with basil flavor enhances many dishes, notably pasta and sliced tomatoes when a chiffonade of fresh basil is not available.
The Equipment You’ll Need
Some food blogger leave some or all of their herbs in the oil indefinitely because they think it’s attractive and more readily identifies that the oil is in fact infused, and with what. We don’t care for that, believing it to ultimately be detrimental to the quality of the oil. It’s decaying plantlife, after all, and we remove it. To do so, you need a sieve with a 400-count mesh. This means that there are 400 openings per inch of material. That is small enough that almost all particulate matter is removed from the oil during filtering.
The second item you’ll need is an airtight container in which to store your infused oil. We like a 17 oz cruet with a rubber stopper. That’s enough infused oil to last 6-months to a year in our household and the ratio of oil to herbs is manageable. However, use whatever container you want, as long is it’s glass, not plastic, has an air-tight lid, and will sit in a cool, dark pantry comfortably for awhile.
The final item you’ll need other than the titular ingredients is time. Plan on a full two weeks of infusion time before straining the oil through the fine-mesh sieve, which also takes a bit of time.
Herbal Infused Oilve Oil
Ingredients
- 2 cups tepid tap water
- 1 tbsp food grade citric acid
- 1-1/2 cups fresh herbs, like basil, oregano, rosemary, tightly packed and stems attached
- 1-1/2 cups acidified herbs
- 17 oz extra virgin olive oil
Instructions
- Pour the water into a small mixing bowl and add the tablespoon of citric acid powder.
- Stir until the acid powder is thoroughly dissolved.
- Place the herbs into the water. Use a plate or a smaller bowl to push the herbs down into the acid water. They must remain fully submerged.
- Cover the bowl with a kitchen towel and allow to sit at room temperature for 24-hours; no more, no less.
- Rinse the herbs and pat dry with paper towels. Allow the herbs to sit on dry paper towels for 2 hours so any residual moisture evaporates.
- You will need a temporary container with a lid that will hold about 24 ounces.
- Rough chop your herbs and crush slightly with your hands as to drop them into the container. This will help release their oils and flavor.
- Measure 17 oz of extra virgin olive oil into the container.
- Ensure the herbs are fully submerged in the olive oil. Put the lid on the container and the container in the refrigerator for 2 weeks.
- Even thought olive oil solidifies when refrigerated, the infusion process will still occur.
- After 2 weeks, bring the container out of the fridge and allow it to sit for 2 hours at room temperature. This will return the olive oil to a liquid state.
- Place a 400-count fine mesh sieve over a measuring cup or other container with a spout, and pour a little of the infused oil into the sieve. It will slowly percolate through the sieve and clear oil will accumulate into the measuring cup below.
- Continue with this straining process until all oil has percolated through the sieve, then place the remaining herbs into the sieve.
- Using the back of a spoon, lightly press the herbs down into the sieve to further extract oil they may be harboring. Turn the mass of herbs over and repeat this process several times. Press lightly; don't mash.
- At the end of this process, you should have something close to 16 fluid ounces of clear olive oil with a slightly green hue in your measuring cup.
- Pour the strained olive oil into your storage cruet; tightly cap the bottle and allow the oil to sit in a cool, dark pantry. It will last a year. It can be used immediately, but you will notice over time that a small amount of very fine particular matter will fall to the bottom of the cruet over time. These are merely particles that were too fine for the mesh of the sieve to trap; but they are still heavier than the oil that surrounds them and will fall to the bottom of the cruet accordingly. When you use all the infused olive oil and get to the bottom of your cruet, leave these particles behind.
Notes
- For acidifying garlic cloves to make garlic infused olive oil, the ratio is different. Use only 2/3 cup of roughly chopped garlic gloves in the solution of 2 cups water with 1 tbsp citric acid.
