Black Oak Blog

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Refraction & Extraction: Notes

by Chris Harris | January 22, 2014 | 0 Comments

 

It’s an odd experience, discovering that the coffee you’ve been brewing for years is not what it could have been, not what it should have been. I’ve definitely had some mediocre stuff in that time, coffee that would bore or even offend me no matter how it was prepared.  There have been some astounding cups, too.  Mostly, though, the middle-of-the-road cup has prevailed.  I have to wonder, then, why were so many so middling?  After a few weeks experimenting with the VST Inc. coffee refractometer, there’s no more wondering.

I’m the kind of person who’s receptive to technology if it makes what I’m doing less complex.  Brewing coffee is, for the most part, following a few guidelines in order to end up at a sensory (perhaps intellectual) experience that is better or worse depending on how you’ve strayed from or followed those guidelines.  But what if the guidelines aren’t clear, or what if you can’t tell if you’re on track?  Two pieces of technology I have acquired for myself since I started brewing specialty coffee at home, a gram scale and a conical bur grinder, are now indispensable.  I would not want to brew without them even once. 

VST’s refractometer is a pinnacle among the lesser peaks of coffee tech, however.  Why go to the trouble of measuring things like total dissolved solids (TDS) and extraction percentage?  Just as finding precise coffee and water weights are essential to my brewing process, TDS has become an element of that process I wouldn’t want to be without.

Putting it simply, the molecules that make up coffee flavor and aroma are embraced tightly by the bean and its cell structure, and to release them from the bean’s bear hug, you need a solvent and a grinder.  Water is your solvent.  Heating water increases the rate of solvency.  Grinding coffee increases the surface area on which the solvent operates, and so on.  It makes my head spin sometimes trying to decide what to adjust when it comes to adjusting my brew.  That’s where technology can assist.  The refractometer precisely reflects small changes in dose and grind immediately after brewing, so all that I have to do is keep my deductive wits about me, soaked though they be in caffeine, and record what small changes I’ve made and the corresponding readings so as to learn something after all the experimentation. 

Changes to what end?  Twenty percent extraction is the target, and twenty tastes and smells very good, indeed.  There’s a tendency (I own I was once of this tendency) to always add more coffee and grind finer—we want a strong, rich cup, right?  A cup with pungent varietal markers, like bergamot, black tea and elderflower in a Yirgacheffe.  But refracting coffee tells no lies.  At the cupping table, over-extracted coffee, those at twenty-two percent or higher, taste less pungent, less like themselves.  Frankly they are redolent of nothing, smell of soggy cardboard and taste somehow bitter and thin simultaneously.  All that we call varietal character, all that makes one coffee different than another, all that can make a coffee stand out, is smothered or muted. 

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Using my Aeropress, a very quick way of making lots of cups of coffee, and with a fifteen gram dose, a dose that doesn’t require bags and bags of expensive coffee for each adjustment, I decided to dial in that twenty percent extraction at home.  Fifteen-to-one is another standard, this time the ratio of water to coffee.  225 grams of water nicely fills the Aeropress cylinder.  So, 15 grams of coffee it is.  If you need a good guide for how to use an Aeropress, there are plenty from which to choose on the web.  I brew with mine inverted, mostly because I found I can get away with a coarser grind owing to the agitation that comes from turning the Aeropress over before compression.  Otherwise I only give a slight swirl before pressing just to even out the grounds.

As I got closer to the right extraction by adjusting my grind, I still found heaviness that I wanted lifted.  I decided it must be the fines, tiny dust-like particles that break away from the grounds during grinding, that were suffocating my Colombia micro-lot.  So I made sure not to tighten my grinder’s catch-cup too much, and once I had finished grinding, I gently unthreaded the cup—there I found a thick donut of fines around the brim along with a cake of fines, grounds and silverskin static-clinging to the grinder’s bottom bur, all of which I discarded.  I then rotated the cup like a drum, wiping up the fines that clung to the side with my finger.  I repeated this as long as I could stand to (there were still more fines to eliminate), and in the end, I had lost significant mass from my original fifteen-gram dose.  Thirteen-and-a-half grams finally went into the Aeropress.  I though I must be on my way to a skim milk cup.  I was wrong.

My TDS measurement came to 1.13, pretty weak sounding compared to the 1.25 or so I was measuring before.  But calculating with the reduced dose, extraction was still near as makes no difference to twenty percent.  And the cup was incredible—syrupy, like sucking on sugar cane, and in place of the semisweet chocolate I tasted before was a raisin Danish.  I was happiest with the sultanas and dates I tasted, which, along with the molasses-like sugar, combined for a fruity complexity I had not experienced so clearly from this Colombia.  The cup also had a luxurious viscosity while still appearing clear and sparkling when held to the light.  Looking at the puck of spent grounds, my normal method of diagnosis post-brew, only a film of fines lay on top of the crumbling mass, with plenty of grounds piercing through.  Normally the layer of fines is more integral and at least a couple millimeters thick.

At Black Oak our refraction experiments are far from over.  But we have made and are making changes continually in the café in order to improve the coffee we serve.  There’s no question that a little bit of objective score keeping improves the experience.  We’ll furnish updates as the come.

Tagged: aeropress, brewing methods, business of coffee, colombia, extraction, single origin, vst

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