Now is the best time to gather them for human consumption, just as they're ripening and when their colour is brightest.
I took them home, washed them and pulled each small cluster off the main stem. It isn't necessary to separate the individual berries. You'll need about one cluster per cup of water. You can simply crush them in cold water or heat the water first, then soak the fruit until the water is a light pink colour.
The trouble with tannins
Don't boil the berries. They contain tannic acid which is also present in tea and wine. It can cause liver damage if consumed in sufficient quantity, and may cause cancer. Boiling extracts more tannin and only makes the flavour bitter. As with all things, consume sumac in moderation.Probably because of their tannin content, native people found an infusion of sumac berries useful in treating diarrhea.
Whatever ails you this fall season, a glass of sumac lemonade will certainly refresh you. Strain the liquid through cheesecloth, sweeten with honey or maple syrup, chill and serve over ice.
A slightly stronger juice, simmered briefly, is useful in making jelly and jam because its tart flavour complements sweeter or blander fruits like apple, plum or elderberry. Sumac jelly makes a good complement to meats. Melana Hiatt offers more information on cooking with sumac and a recipe for sumac-elderberry jelly at The Edible Wild Kitchen. You'll also like Melana's Suite101 topic: Edible Wild Plants.