First a simple syrup for in-season fruit.
3 peaches, chopped
1 1/2 cupswater
1 1/2 cupssugar
Typical syrup for cocktails is usually 1:1 water to sugar. I like those proportions. For fruits like berries and peaches, I just throw all the fruit, water, and sugar into a sauce pan and cook, removing from the heat just before it boils. Be sure to strain the fruit out of your syrup with cheesecloth and store it in the refrigerator. It lasts about 1 to 2 weeks, more if you add a spirit to it, such as a tablespoon of brandy for peaches, rum for berries, cognac for cherries, bourbon for mint, chartreuse for rosemary/herb, etc.; you can't do it wrong if you are happy with the results.
16 ounces strawberries, chopped
1 foot long stalk rhubarb
1 1/2 cups water
1 1/2 cups sugar
For the above recipe, rhubarb doesn't lend itself to syrup like a berry, so first chop the rhubarb slightly in a food processor until it gives up some of its juice. Then combine with the strawberries, water, and sugar and cook like the peach syrup recipe.
What about the vinegar? Well, you can turn any syrup into a 'shrub' if you add cider vinegar at a 3:2 ratio of syrup to vinegar. Be adventurous and give it a try. The following cocktail would be awesome with either strawberry-rhubarb syrup or shrub...
2 ounces dark rum (I used Old New Orleans)
1 ounce strawberry-rhubarb syrup or shrub
1/2 ounce Aperol
Dash Angostura bitters
1 1/2 ounces Applejack
2 ounces peach syrup
2 dashes Peychaud bitters (you could substitute with a dash of Herbsaint or other licorice liquor)
Dash Blue Curacao
Both cocktails are stirred in a mixing glass. Strain, garnish with mint, and enjoy.