Here's a great article in The New York Times about cold-brewing coffee and tea.
I've never bought into the cold-brew, having tasted some before and found it lacking. This story explains why — because the hot and cold products are chemically different from each other:
Hot water also cooks as it extracts, forcing chemical reactions that transform some of the extracted substances into other things, and driving some aroma substances out of the liquid. Cold water, in contrast, extracts more slowly and selectively, produces a simpler extract, and doesn’t change the original flavor substances as much.
So cold-brewed teas and coffees are chemically different from their hot counterparts. They tend to contain less caffeine and less acid. And, of course, they taste different. If the flavor of hot tea or coffee is your gold standard, then cold brews won’t measure up.
I make plenty of iced tea during the summer — just enjoyed another pitcher of TG's Manjhee Valley first-flush, which does well over ice — but I prefer a strong hot brew poured over ice. You?
Then again, hot and cold have always been fighting.