sumac

Sumac is often regarded with fear and suspicion because of its toxic namesake— poison sumac. Caution should always be exercised when dealing with harmless plants that have harmful counterparts, but in this case, these two plants are distinctly different in appearance. The surest way to tell them apart is by the color of their drupes: poison sumac (Toxicodendron vernix) sports hanging clusters of white berries, while harmless varieties (Rhus) display erect panicles of brick-red berries.

The variety that I'm most familiar with, Staghorn Sumac (Rhus typhina), is native to northeastern US and Canada. At this time of year— with the leaves nearly gone and the silvery splayed branches exposed— it's easy to see where it gets its name.

Culinarily, sumac has a long history in the Middle East and along the Mediterranean, where it is ground and used in powdered form to add sour notes to mezze and meat dishes. A popular seasoning, Za'tar, is a blend of thyme, sesame seeds, and sumac. 

In North America, sumac is rarely used outside of ethnic dishes, although it was widely used by indigenous people to make a sour beverage similar to lemonade. The late Euell Gibbons, who introduced Americans to wild foods, was very fond of the beverage and dubbed it Rhus-ade. There is a story that tells of his use of an old washing machine exclusively purposed for Rhus-ade, in which he made large batches by loading the tub with sumac panicles, running them through a cold water cycle and catching the liquid as it drained.

Sumac has little aroma and a flavor that can be almost entirely defined as "sour"— largely due to malic acid, and, to a lesser degree, citric and tatric acids. The acids are concentrated in the tiny hairs that cover the berries and are water soluble. Most recipes that I've seen recommend cold water infusions, warning that hot water draws out the undesirable tannins. This, I assume, is true when using the panicles where the berries are still attached to the stems, as the bark and leaves are richly tannic. Historically, sumac was used to tan hides and is still used today to produce high quality leathers such as Morocco and Cordovan.
To test flavor concentration in various temperatures of infusion, I made three controls of just berries and one with berries still attached to the stem. All were strained after 3 minutes, then chilled for 30 before tasting.

sumac-water infusions, left to right:

berries in cold (5C/40F) water— faint color, bright flavor, pleasant acidity, no aroma
berries in warm (38C/100F) water— pale color, bright flavor, pleasant acidity, faint aroma
berries in hot (90C/200F) water—medium color, bright flavor, slightly sharper acidity, faintly musky, faint cider vinegar aroma.
panicles in warm (38C/100F) water— faint color, less bright flavor, slightly less acidity, no aroma

In conclusion, I favored the hot water infusion. It was barely perceptively more acidic— which suggests that higher temperature does not extract more acid (wish I had ph strips to know for sure), but heat seemed to draw aroma from the sumac and coax out more of its essence.

A sweet and sour syrup is a useful thing to make with sumac.

sumac syrup 

2 parts water
1 part sugar
1 part sumac berries 

Measure quantities by weight. Bring the water and sugar to a boil. Pour over sumac berries in a heat resistant vessel. Allow to infuse for 5 minutes. Strain, first through a sieve to remove berries, then through a micro filter or several layers of cheesecloth to remove fine hairs. When cool, bottle and store in refrigerator.

And, a cocktail is a useful thing to make with a sweet and sour syrup.

sumac-lemongrass vodka sour

2 parts lemongrass-infused vodka
1 part sumac syrup
ice
fresh lemongrass stalks 

Pack a cocktail shaker with ice. Add vodka and syrup. Shake. Strain into tall glass. garnish with lemongrass stalk.