Since Seattle's mini heatwave of last week, I (Nate) have been musing on various delicious ways to consume cold coffee.
After poking around the net, the most useful post I've found on the subject is an August '09 post from Daniel Humphries' blog. Relevant post here.
I can't improve on Daniel's lazy man's cold brew, so I'll repeat it here verbatim:
1. Brew a pot of French press at 140% strength (that's 84 grams to the liter, or exactly 12 standard seven gram scoops in an 8 cup press)
2. Pour immediately over ice
I like that Daniel's method allows a quick 4 minute iced coffee preparation and allows the coffee to cool quickly without becoming diluted. The strongest part of the blog post, though, is Daniel's description of the volatile organic acids that extracted from the grounds during a hot brew process. These are a subset of the dissolvable flavor compounds referred to in my recent 2 part post on brew colloids and the Coffee Catcher (1 and 2). Organic acids in coffee tend to stand out as flavor highlights on the palate, but are fragile and decompose rapidly. Decomposed acids taste bitter, and this is why Daniel recommends a hot brew followed by very rapid cooling to preserve that fleeting complexity in the cup.
The other major cold brew school is toddy. The moniker comes from toddy equipment maker Toddy Cafe. Making toddy is easy: mix a relatively high dose of coffee (at least double normal, Toddy Cafe recommends a quad dose) with room temperature water and brew for at least 12 hours. Dilute to taste and serve. Because temperatures never approach those needed for organic acid formation, toddy coffee remains smooth and approachable regardless of brew time, although the trade-off is significantly reduced flavor complexity.
Here's my question. Why does a toddy brew require a massive updose? Extraction may be slower, but total extraction of coffee compounds during the cycle seems comparable to a hot brew. Caffeine content is certainly there, as I can attest after a recent cup of Toddy at Aster - and that's after dilution. Ice dilution should be even less of a factor with room temp coffee than with a hot brew, so my intuitive sense would be a dose in the 120% range. If extraction rates and dilution aren't in the picture, what else is going on to justify double to quadruple doses?
I'm a card carrying advocate of the "if it tastes good, it is good" school, so if it just tastes better, that's a good enough reason for me. My question, though, is why? And also, has anyone tried brewing toddy at normal strength for comparison? Comments welcome.