I also did one more this weekend - pushed a small batch of India well into near-vienna (just a hundred grams). Beans all nice and oily, very dark and smoky. Beautiful batch emulating the darkest of a *$s Sumatra.
Had enough for 3 cups (couple days rest) - normally extracted (inverted AP), very full flavor and smoky - a homey kind of smoky, not the burnt or scorched flavor I expected, but definitely overlaying the flavor. Some not too unpleasant bitterness accompanied by a very nice toasted caramel/cocoa reminiscent of a s'more without the marshmallow.
Aeropress "recommended" - smoke and bitterness muted - but so was a lot of the cocoa notes. Some varietal character, body not as thick as normal extraction. Some touch of malt, unexpected.
This morning, cold brewed results from overnight (about 12 hours). Yep - basic coffee with only the slightest hint of anything resembling bitter. Lacking in complexity. Not bad but not much different than just about any run-of-the-mill coffee.
I think that personally, I'm probably done with cold brewing coffee - the cheap engineer in me sees it as a waste of potentially extractable solids. LOL
Technically speaking, no, not room temp water from first brew all the way sitting on the counter to the end of 12 hours. I have varied initial brew temperature downward, though, and find that the extraction for a given brew ratio seems to level out much below 150°F toward the cold brew extraction percent.
Stated differently, if a particular brew ratio (say 21% brew ratio) seems to yield around 16% extraction when cold brewed, then if you start at an initial brew temperature much below 150°F the extraction won't be much better than that. It seems to take the temperature to get the locked-in character of the coffee that lowered temp brewing just won't pull out if the temperature isn't high enough. The difference between 38°F and 72°F is just not that big a deal. The volatiles we're looking for need extraction solvent above 170°F to extract them.
The flavor, also, seems to follow the extraction, which is one of the things that made me think about the hypothesis of why cooler brew temps have lower brightness and smoother overall character, with less varietal flavors. That's why I think an Aeropress with 170°F brewing temperature is somewhere between a fully-extracted brewed coffee and a cold brewed coffee. It's right on the edge of being able to get those fats, fatty acids and aromatics that require energy for extraction.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
I have quick&dirty reproduced your research and compliment you on it. Thanks a bunch!
It inspired me to try a two stepped extraction: First step As described by you: 6h cold extraction of 15% fine grounds at fridge temperature (7 degC.), separated by AeroPress. [Use reversed extraction at your own peril ;-) The cold shrinks the seal on my plunger, causing leakage.]
Second step Gently pull up and remove the plunger of the AeroPress, and push the puck back down, if necessary. Re-hydrate the puck with hot water [I used water at 97 degC.] and strir it into suspension. [Since It uses hot water, I could do this step by reversed method.] Press this hot extract into a separate receiving vessel. You can cool this down to the same temperature as the cold extract, or blend it while it's still hot with (part of) the cold extract.
This second extract contains most of the goodness the cold extraction left in, so blending it into the cold extract compliments and enriches it. Since it is a (visually) weaker extract it will also dilute it, though naturally less so than plain (hot) water would. Mix and match to taste and / or stomach sensitivity. Yes, this two-step extraction makes for much fun experimenting!
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