Choose a 16-ounce bottle with a well-fitting lid or cork. Boil it to sterilize, then remove from 'water bath', empty of any water inside, and allow to cool to room temperature.

In a small saucepan, combine the vinegar with 1/3 cup of water and heat until the mixture begins to boil. Remove from heat.

Slip about 3 sprigs of fresh rosemary into the cooled bottle.

Using a funnel and care (!), pour the hot (NOT boiling) vinegar into the bottle over the rosemary. Cover tightly with lid and store at room temperature.