Oils create an environment with no oxygen, which is an ideal place for Clostridium botulinum bacteria to grow and produce botulism toxin.. Since produce items like garlic and herbs can harbor C. botulinum, it’s a good idea to destroy any bacteria on those items before adding it to oil. This can be done by soaking the products in a citric acid solution to reduce the pH and destroy bacteria that might be present. Specifically, the citric acid solution needs to be strong enough to bring the pH level of the garlic, herbs or other ingredients down to 4.2 or less within 24 hours.
How to safely infuse oil: https://news.ncsu.edu/2019/12/infused-food-safety-tips
https://www.foodprotection.org/files/food-protection-trends/Jul-Aug-14-Abo.pdf
Skipping the acidification step is risky, so refrigeration is important to prevent the growth of bacteria.The oil or honey should also be heated to 180 degrees Fahrenheit before adding it to the other ingredients.
