Prufrocker: The Blog

The Test Roast Solubility Quality Check

Until recently at Prufrock we cupped for fun, but now we cup to find out what’s going on with you Roasters!

by  |   |  Coffee Science, Recipies


The cupping protocol with the same grind setting, water temp and brew ratio is well established and international. Scott Rao uses it. So do we. He says in his recent masterclasses at Prufrock, ‘we do it to find out what’s going on with the coffee.’ What was it about this comment that so much made the penny drop?

An obvious comment, but it came during question time after an incredible 90 minutes of discussion about the 3 commandments of roasting. He made continual reference to the idea of good development, not as a phase in the roasting process, but as the condition of well roasted beans. High solubility, no noticeable roastiness and a high threshold of extraction levels before astringency kicks in were his barometers of good development.

I do feel us baristas have shouldered the blame for poor extraction over the last five years since roasters have been lightening up their roasts and learning how to roast with better coffee beans. We knew six or seven years back we had to drop doses down from the Aussie style 21-21g; the millennial dose as Fresh Cup has quoted us last month. We got down to 66% four or five years ago and I remember it felt weak at the time. If I look in the C Harmon archives I can find a post all about the wonders of 1.55. I looked back at my own Refractometry handout for courses and saw a diagram of a refractometer with 18-30g written on it and 11.6% TDS written as the very unrealistic target. The double hump post was written in the heart of this period and I remember we spent a lot of time staring at our refractometer blaming the grinder and lamenting lower than desired TDS readings and looking around for something to blame: the RO system, or the burrs weren’t sharp enough and fines production was excessive or channelling was going on.

Mean while in 2010, debate raged as Steve Leighton put out the polemic of omni-roasting, a term I’m pretty sure he coined. And all the while we were using a 66% EBF, and brewing with what we would now regard as baked coffee. Mr Rao’s book has made me feel quite a bit exonerated, pointing to breaches of the three commandments of roasting that left us in extraction-purgatory between 16 and 18% for so long. A comment from Gwilym on this subject which really blows the roof off this debate is this: “Roasters purposely making their coffees only taste good when up dosed is ridiculous, much better plan for the future is to extract more from each bean and pay for better quality.”

The missing link in our QC; the Scott Rao induced eureka moment for me was realising we’ve been focusing all our energy and scientific rigor into our espresso QC. This was a natural thing to do because it was so much less reliable over the years, but by focusing on the method of preparation so much, we overlooked the raw materials. A million syringe filters later, we have a very large collection of 4s and 3.5s out of 6 in our online espresso QC journal but not very much cause and effect stuff to take from it.

Everyone cups because it’s just coffee and water and a bit of a stir; there’s no channelling; there’s good thermal mass; not much evaporation; long established and sensible protocols. There’s everything going for it to do all it needs to in an empirical way more or less. But, if we could just apply the same ice cold precision we have when we pull shots and fill out our espresso journal each morning; weigh the water, and take mojo readings of every sample, and ‘see what’s going on with the coffee’ we could find out if the best coffees make the best espressos. And so we’ve started weighing the water into the cupping bowls, grading out of 100 and taking TDS readings of every sample at the same interval of time four times a week. The beauty of it is that a simple definition of good roasting has emerged already through this process. The best roasting of a coffee for us is the one with the highest aggregate score of it’s green grade and extraction yield. This is the basis of omni-roasting in my opinion. If it gets 116points, it’s good for espresso. If I throw in a disclaimer, I’d say it’s good for espressos up to a 50% EBF.

Take a look at our new Test Roast Solubility Check protocols. I’ve popped them in a Dropbox for anyone who would like to use them. So here’s what we do the two mornings following on from our twice weekly coffee deliveries.

https://www.dropbox.com/s/4llw2cit9kmlytj/TestRoastSolubilityQualityCheck.docx.pdf?dl=0
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The QC protocols we are using are based on the SCAA Green Grading system but for accurate readings you must weigh the brew water and we suggest four identical cross stirs at 4mins to the base of the cups. Our plan is to order in the coffee with the best combined score for solubility and the highest grade. The QC is happening four times a week on the two days after each delivery.

This process is an educational vehicle as much as anything else. We are teaching all our baristas to green grade by inviting various Q graders to help us calibrate as often as possible. Thanks to John Ivar Sørreime from Kaffa Oslo for helping us calibrate last weekend. Jochem Verheijen, the wonderful head of coffee at HH was in this Saturday. We will also be scoring guest coffees from JB, the Barn, Roundhill, Koppi, La Cabra, CC, Lomi, Casino Moka, Double Shot etc which may be of interest to any would be subscribers.

The hypothesis we’re using here for the choice of espresso offering and this touches upon our approach to omni roasting is that a coffee that cups up to 22% extraction with no roasty flavours and no astringency is the right choice for a 40% brew ratio. I cupped the Square Mile Gathiga AA and scored it at a glorious 87.75 with a record solubility of 22.8% and it is straight away top of the list for brew bar or espresso next order. The intention is not to order it blindly as an espresso coffee. It might get a little confronting as an espresso but it has all the odds in it’s favour.

So Scott has made me realise until recently at Prufrock we cupped for fun, but now we cup to find out what’s going on with you Roasters!