Wednesday, June 16, 2010

Brew Colloids and Fine French Press Flavor: Part 2 of 2

Brew Colloids and Fine French Press Flavor: Part 2 of 2
by Nate Jones
(Read Part 1 of 2)

Last week's tech-a-thon was all about how brew colloids, tiny masses of fine coffee and oils, trap flavor solids. The post concluded with the suggestion that the Coffee Catcher may allow active colloid management for the first time. First off, this article should be taken as an invitation to explore further - not the definitive truth on the Coffee Catcher's role in French press brewing. After six months of daily brewing, I've developed enough ideas to lay out some questions I'd like to discuss further, and this seems like a good time to invite the coffee community to weigh in.

One of the most consistent test results we've had with the Coffee Catcher has been apparent direct filtration of a significant % of brew colloids, with colloids separated from the brewing area and the cup by the stainless Coffee Catcher disc in the carafe. Coffees have tasted cleaner and flavor profiles have held up longer. At first, my assumption was that the key variables in this filtration process were the size of the mesh and the strength of the pressure wave generated by depressing the plunger in the French press. However, Sam Lewontin (@coffeeandbikes) pointed out that Scott Rao has argued that cleaner flavor comes not from a finer filter that traps more colloids but from the physical arrangement of the brewing system itself that either naturally separates heavier colloids or does not. 

Thinking in terms of brewing systems rather than mesh size, I now suspect that most of the filtration occurs in the first few seconds of the brew, as water is being poured over the bed of coffee on top of the Coffee Catcher. The turbulence and downward pressure generated by hot, falling water generates an initial mixture of coffee and water, and I think that that heavier colloids may naturally separate so that colloids are pushed beneath the disc by water pressure and turbulence during these first few seconds. Colloids would then be kept from brewing with the coffee from the start of the brew. In that situation, the cake of grounds atop the disc would effectively plug the press and keep filtered colloids from entering the cup when the press is emptied.

So here's the question: I've been able to achieve "full" filtration using the Coffee Catcher disc with a regular pour of hot water. I've also achieved apparent zero filtration multiple times by deliberately pouring very gently and slowly directly over the Coffee Catcher. So if no filtration and "full" filtration are possible, would it be possible to vary the pour pressure to achieve different levels of filtration? Think Hario pour overs, but for French press.

Another potential brewing system tweak introduced by the Coffee Catcher is a more effective French pull, a technique referenced in a thread over at During a marathon brew session a few weeks ago, Alex Negranza (@Barista_Alex) and I experimented with bottom filtration of the press - pulling the Coffee Catcher immediately after the brew cycle was complete.* To our palates, the results were distinctive and intriguing, including a softer mouth feel and a seemingly rounder flavor profile with more fruit. In system terms, pulling the Coffee Catcher seems to filter very fine coffee solids in the foam and the brew, but doesn't seem to remove brew colloids filtered beneath the disc.

So here's the question: does the Coffee Catcher indeed produce a French pull with a distinct flavor profile relatively easily? If so, how and why is this making a difference relative to traditional French press techniques?

Finally, Alex has written an interesting post over here about siphon filtration using a modded Coffee Catcher. The common theme with the French pull above is vacuum, or bottom filtration of some sort. I'm all questions on this one. What exactly makes bottom filtration distinctive? Is it only that filtering from the bottom keeps fines at the top of the brew from coming through, as Rao has suggested? Is a relatively mild vacuum beneficial in flavor extraction terms? Can bottom filtration be tweaked (either by modifying pressure or mesh size) to extract a more desirable flavor profile? 

So, that's where I'm at. The Coffee Catcher will soon be in the public domain, and I hope sharper minds than mine will tackle some of these Q's - brewing up delicious coffee along the way!
* Please Note: this involves getting fingers close to hot coffee, and you could be burned. Try at your own risk! In practice, it seems the surface of the coffee cools extremely rapidly, and I've yet to burn myself touching the surface of the coffee during a pull - even immediately after brewing. Nevertheless, you should use your own judgment and proceed with caution as you try this.

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