by fun_yunchables » Mon Nov 16, 2015 7:48 pm
adding onto deadkitty's reply, this is kind of what i've learned re: science of coffee:
gesha is a varietal which is usually valued for its distinct floral and citrus tasting notes. so most people tend to roast and brew gesha in a way to highlight that flavor, ie filter coffee.
gesha is actually an african coffee which was transplanted into latin america (it's actually the name of a region in ethiopia). the thing is there are so many variations of coffee in africa alone, which is why you commonly see african coffees referred by the region the trees are in (yirgacheffe, guji, sidama, etc etc). but many famed geshas are in fact from latin american farms such as finca el injerto.
cold brewing as a method of coffee brew tends to even out extractions. i think i might have talked about it in a previous post, but the primary compounds which give coffee it's flavor are acids, sugars, and bitters. acid molecules are smaller than sugars which are smaller than bitters, so typically the diffusion of acids is on a faster time scale than that of the sugar and bitter molecules. when you increase the temperature of the medium (the water), the difference in diffusion speed is magnified. conversely, when the temperature decreases, the diffusion rates grow closer to one another. maybe a numerical example might make this clearer?
say for 98C we have acids extracting at 10, sugars extracting at 5, and bitters extracting at 3 (unitless, just for the concept). when we brew at 12C, it might be closer to acids being 4, sugars 3.5, and bitters 2. so the coffee you brew is much more evened out. now for a gesha, balance is something that brewers might not initially think about, as the desire is to highlight that natural floral and citrus flavors--for the most part, acidic compounds. a cold brew will lead to a more balanced brew, while typical filter coffee at higher temperatures allows us to extract more of the nice acids without too much in the way of sugar and bitters.
re: peets' (stumptown's) gesha cold brew, i'm a little skeptical but i think everything is worth at least a try. might be pleasantly surprised by the complexity of gesha cold brew, but who really knows until you try it?
edit: woops made a mistake in the numerical example, fixed now!
Last edited by
fun_yunchables on Fri Jan 08, 2016 2:21 pm, edited 2 times in total.
coolest lame guy u'll ever meet