Wednesday, May 4, 2011

18:22!? - The Ironies of Coffee's "Magic Window"

Every coffee lover ought to be familiar with the magic window for coffee: 18-22% of extracted solids are considered the optimum ratios to produce a good cup. Now, this range comes loaded with as many caveats as there are baristas.

While everyone has their own take on the flaws and benefits of the "magic window," I thought I'd scribble down a few of the more confusing ironies that come with having a widely acknowledged but rarely followed industry quality standard.

1. It's really a fuzzy continuum, not a range per se. The range is based on aggregated taste preferences, and the survey itself has not been updated in years (decades?). In other words, the window represents the average preference of the tested coffee drinkers when the survey was conducted. Frankly, it may or may not have any relationship to your preference, and as such it's claim to be normative quality standard (i.e. you "should" brew this way) will always be somewhat shaky.

Here's the really interesting part about that: coffee drinkers seem to prefer different extraction ratios for different coffees and brew methods. Coffee lovers who relish their French press of Sumatra every day may well prefer a technically over-extracted cup, because that's what a good press of Sumatra tastes like to them. Those same drinkers, though, may prefer espresso to be properly extracted. In other words, in the real world context influences our taste perceptions far more than we coffee nerds would like to admit. This alone, I think, should give those of us who work in coffee a degree of humility when assessing the quality of a particular coffee bar. Are they serving to the taste of their customers? Recommendations for increasing coffee deliciousness should proceed with that in mind.

2. The 18:22 window can't describe evenness of extraction, a point ably brought to my attention by James Hoffman. In other words, you may get 20%, but there's no guarantee you're not pulling 24% at the top of the brew and 16% at the bottom, which would likely not be tasty. I've noticed this point myself when experimenting with innovative French press techniques, as I try to avoid problems of uneven extraction problems using a traditional wait-and-press method. Evennness matters because uneven extraction yields a partial picture of the coffee. You're missing some of the taste symphony in your mouth.

3. Some beloved brew methods rarely hit the window. I'm thinking particularly of French press and cold brew here. For the press, the lengthy rectangular brewing chamber coupled with a traditionally coarse grind, lots of bloom and long immersion time yields a wide disparity of coffee concentration from top to bottom of the brew chamber. The resulting brew is loaded with fines and starts with a hint of bitterness that only grows with time. Yet, those coarse particles don't fully extract, as anyone who has compared a cupping table with a French press will attest. Traditionally prepared presses are just not good at bringing out a coffee's delicate notes.

Cold brew actually under-extracts, despite it's reputation for fierce caffeine content. Again, while the cold temps are known for not generating acidity during brewing, they also fail to fully extract the flavors associated with that acidity - that popping green tomato in some Kenyas will fall flat in a cold brew every time. Don't get me wrong, I love a cool tankard of iced in the summer, but I know I'm deliberately trading out nuance for the coffee equivalent of smooth power.

These two brew methods are not the only serial offenders when it comes to routine over or under-extraction. The difference is that many of us seem to enjoy these brew methods prepared this way, whilst there seems to be less patience for an over-extracted shot or a sour, under-extracted pour over.

4. Finally, the window is not equally delicious. As a (very) general rule, it would be ideal to extract a coffee as close to 22% as possible without going over. The problem is that the exact "red line" will vary slightly by coffee (by bean!) and this slight natural variation coupled with the human challenge of brewing consistently yields an exponential rise in risk as a brew approaches 22%. While widespread measurement of extraction percentage remains elusive (another discussion), I think one of the marks of a good barista is his or her ability to walk that line, crafting a great brew that holds as much of the coffee's flavor as possible - without tipping over into bitterness.


Fragmented tasting preferences: who says your cup tastes good?

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