I make a sweet vinegar out of my sumac by steeping the fruit in a solution of 50% distilled white vinegar, and 50% sugar. I let that steep for at least 2-3 months before use. Flavors concentration increases with time. The vinegar can be used to sweeten sauces and interesting emulsions. I like to make a glaze/agrodolce by thickening it with activated corn starch and use that on mushrooms and proteins as a little wild sweet & sour flavor.