How to save fresh basil?
You may freeze it or dehydrate it. I keep some of both. Some people take ice trays and put fresh basil leaves in the tray and fill with water and freeze. Then when you need them for stews or soup, you just throw the appropriate number of them in the soup or stew. Otherwise you may wrap the leaves in freezer plastic wrap. To dehydrate them, I have bought an inexpensive dehydrator with stackable trays which dehydrates them in about an hour.
