Prufrocker: The Blog


Getting rid of the quakers and chips and all manner of secondary defects in our coffee. How can we do it more efficiently?

by  |   |  Competitions, Tips & Tricks

At the Rimini 2014 World Brewer’s Cup, Petra Strelecka, Adam Obratil, Jan Hrna and myself collaborated in what we call re-processing. For many years we have been sorting out quakers and chips and all manner of secondary defects in our coffee. Parchment covered beans are considered by the SCAA to be secondary defects. 2-3 instances constitute a full defect. No more than 5 full defects are permitted per 300g of Speciality grade coffee, which means any more that 10-15 parchment covers beans per 300g would make a coffee score below 85 points. No one to my knowledge has made the World Brewer’s Cup finals with a coffee that scored below 85 points. In 2013 Isa Verschragen of the Barista Guild of Europe fame noticed that silver skin might be held by static in the throat of the grinder. She went on to win the UK Aeropress with a method that didn’t thwack the thwacker of her Tanzania. Her friend Jeff Verellen has had prodigious competition success removing chaff using static electricity. Adam Obratil here takes a novel approach with a similar idea. What Petra Strelecka in her World Brewer’s Cup Finals routine did that I have never witnessed before was to surgically remove the silver skin out of the bean’s centre cut entirely.

I have cupped silverskin before and especially in the case of black honey processed coffees, have not objected to the flavour at all. With black honeys it can just taste like cascara. But once we really got into cupping our re-processed cups against their un-polished equivalents, we found the aroma was dramatically different. And in double-blind cuppings it was resoundingly obvious that the silver skin was absorbing roasting smells. Not dry distillation aromas, more the greasy grassy smells you pick up half way through a roast. It’s the smell you pick up on the canal around Broadway Market as you walk between Square Mile and Climpson and Sons. It’s not a bad smell, but in the cup it’s not a quality roasted coffee smell, it’s a secondary defect, like a half fried onion. It’s very mild in the scheme of things but it’s absence does make you score a coffee a couple of points higher for fragrance, aroma and flavour.

Think of the silver skin a bit like a t-shirt in a smokey house party. There is some evidence from Scott Rao that says the silver skin is in-soluable. We can however testify to it being absorbent. Absorbent not just of roasting odors, but likely also gungy water and residue during fermentation and washing.

Some roasters are more affected by this that others. Petra was using Dumerso from Tim Wendelboe. I can tell you Mr Wendelboe’s silver skin is a good deal less fumey that most. I would say more clean air during roasting would help. It might be interesing to hull the beans post roast. This would cause plenty of chips, but we’ve never been too worried about post roasting chips. We were often re-processing the beans 12 hours before grinding and not noticing a loss of aroma. Petra had 8.5s for aroma scores.

The most exciting element of competition is that baristas are continually contributing to machine development and sharing their discoveries and are coming up with most of the ideas that drive our industry. Some critical feedback Petra’s judges did have for us during debrief was that they felt the concept didn’t have a commercial reality, and was not a realistic Modern Brew Bar concept. I can’t argue with this. It did take us 45min per 15g. Brew Bars themselves are starting to appear un-realistic modern cafe realities judging by the proliferation of bulk brewing devices in the mid town area.

So we hereby submit an idea for the record we are looking to develop into a fast and workable prototype.
We’re after a re-processing device that pre-breaks the beans, removes the silvershin entirely. It certainly helps that it weighs less than you average coffee grind.  Static? Air? Reverse sieving with a hoover? I’ve had some not inconsiderable success with this, @sprudge in the form of Eileen Kenny was in fact on the scene to witness the event.

Re-processing in action.


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