Dried herbs tend to produce the most effective medicinal vinegar extract, but fresh herbs can be used to make nutritive flavoring vinegars for culinary recipes, since the vinegar will extract minerals as well as the flavor of the herbs. My favorite vinaigrette is made with fresh nettle and mugwort-infused vinegar, but thyme, oregano, garlic and rosemary are nice, too. Dried herbs are preferred when making vinegar-based medicinals since fresh herbs will surrender their juices in the solution. This juice tends to water down the extract and saturate the solvent (vinegar) before it has time to draw out the more powerful constituents you are looking for in a medicine. Powdered herbs are recommended due to the increased surface area of herb they offer in the extraction.