If garlic can't be safely stored in oil for more than 24 hours (due to risk of botulism), what about vinaigrette made with garlic?
We consulted Dr. Linda Harris, associate director of the U.C. Davis Western Institute for Food Safety and Security. According to Dr. Harris, homemade vinaigrettes that contain garlic don’t present a botulism poisoning risk because the acid in vinegar inhibits bacterial growth, particularly if the oil and vinegar separate so that the garlic is sitting in vinegar alone. For added safety, said Harris, the dressing can be stored refrigerated. The same advice holds true for vinaigrettes made with other flavoring ingredients that can potentially harbor botulism spores, like shallots and fresh herbs.
Quality, though, is a different issue. We found that a simple vinaigrette made with 1/3 cup of vinegar, 1 cup of oil, and 1 teaspoon of minced garlic only lasted for 24 hours in the refrigerator before the garlic started to taste “pickled.”