Does salt prevent botulism when you use it to preserve herbs in olive oil?
It is not safe to preserve herbs in oil for long term storage. Salt will not prevent botulism. Here is advice from the National Center for Food Preservation:
Herbs and oils are both low-acid and together could support the growth of the disease-causing Clostridium botulinum bacteria. Oils may be flavored with herbs if they are made up for fresh use, stored in the refrigerator and used within 2 to 3 days. There are no canning recommendations. Fresh herbs must be washed well and dried completely before storing in the oil. The very best sanitation and personal hygiene practices must be used. Pesto is an uncooked seasoning mixture of herbs, usually including fresh basil, and some oil. It may be frozen for long term storage; there are no home canning recommendations.
Let me know if you have any other questions.