Iced Tea: (Not) Taking the Heat
By HAROLD McGEE – Excerpts from the NY Times July 19, 2011

ICED teas should be some of summer’s simplest pleasures, especially when we just steep them in cold tap water, with no kitchen heat and next to no effort. But if you make even a desultory search for advice on cold brewing, you may find yourself mopping your brow deciding how, and even whether, to proceed.

Ratios of tea to water differ wildly from recipe to recipe; brewing times can be minutes or hours.
I’ve found it calming to take a leaf from China and Japan, where one batch of tea is briefly infused as many as seven or eight times and each infusion enjoyed for its particular qualities. Variety can be just as pleasing as consistency, and it can be a way to discover new sides of our most familiar ingredients.

When we brew tea, we’re doing a very basic thing: bringing plain water into contact with dried plant materials to imbue the water with flavor, color and various active substances, like caffeine and antioxidant polyphenols. It is a basic process, but not a simple one.

As water moves into the tea leaves, it dissolves or suspends hundreds of different substances and extracts them from the solids. If the water is hot, it extracts more rapidly and completely. 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 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 is your gold standard, then cold brews won’t measure up. If you think of hot and cold brews as different drinks, just as a lager isn’t the same as pale ale, then you may find that you enjoy both.

The standard proportions for American iced tea are about 4 teaspoons or 2-gram bags per quart, with a brewing time of 8 to 12 hours. In Taiwan, where cold-brewed tea has become increasingly popular in recent years and spurred studies of its chemistry, about twice that ratio of tea to water is used for a similarly long infusion. And one purveyor of fine Japanese teas in Kyoto recommends making small cups of cold Sencha with 5 times that ratio, infusing first for 15 minutes, then for briefer times. The first couple of infusions are like no other version of green tea I’ve had, intensely grassy and bitter, with subsequent brews progressively milder and more refreshing.

Since cold infusion is a relatively slow and gentle process, proportions and times aren’t critical. There’s plenty of leeway for both. As a general rule, the more fragile the tea leaves, or the smaller the particles, the less tea and time you need to get a strong brew. If a cold brew infuses too slowly, just add more tea. Less heat may mean less flavor in teas, but not necessarily less pleasure.