This garlic infused oil procedure was developed after researching how to make garlic infused oil only to find that you have to be very careful when working with garlic, especially raw garlic in oil. Apparently, unrefrigerated garlic in oil can promote the growth of C. botulinum bacteria without affecting the smell or taste of the oil or the garlic. C botulinum causes botulism, a serious form of food poisoning. The toxin produced by C. botulinum is destroyed with heat and acid. The Food and Drug Administration (FDA) now requires “that all commercial garlic in oil products contain specific levels of microbial inhibitors or acidifying agents such as phosphoric or citric acid.“
So here’s what I deduce from my research: To ensure that the roasted garlic is safe to eat, it needs to be in an acidic environment (less than 4.6 pH), heated, and kept refrigerated; thus the addition of the lime juice (pH=3), the long roast and the refrigeration in my recipe. I’ve made many, many batches over the years and I’m still here to tell the tale.
One of my readers brought up a question about heating extra virgin oil and that it’s something that shouldn’t be done. I had heard this comment a while back as well, so I did some research on it. According to a 2007 study published in the Journal of Agricultural and Food Chemistry, extra virgin olive oil (EVOO) heated for 36 hours at 180 C (350 F) “exhibited a high stability against oxidation” and, “despite the heating conditions, EVOO maintained most of its minor compounds and, therefore, most of its nutritional properties.”
This article “Is it safe to cook with olive oil?” does an excellent job of researching the science behind this question and found that the answer to this question was YES.
The main issue with heating any oil is its smoke point which is different for each type of oil. The Olive Oil Source and the International Olive Oil Council both indicate the smoke point of olive oil, even extra-virgin olive oil to be well above the 325 F required for this recipe, in fact – closer to 400 F.