So I did some readings this morning with the VST refractometer.
I'm finishing off a bag of Counter Culture Apollo, 100% Worka Ethiopa, roast date 1/22/19. The roaster says it is agtron 71, but I cannot confirm this, as the contents of "Apollo" rotates through the year. It is a "light" roast, but not as light as scandivian roasts I've pulled in the past.
The coffee was pulled on a Linea Mini with Strada 17g basket, (more or less a LM branded VST style basket). Pressure 9.0 bar, temperature 93c (199.5f). Water is my formulated mineralized blend at about 80 TDS. (find my thread on it elsewhere).
Grinder is the monolith conical, adjusted as needed to produce beverage weight in desired time. Starting point is 29.5 out in 30 seconds, as measured with an Acaia Lunar scale.
Dose is as weighed in basket.
I use the VST recommended process to measure TDS. VST recommends drawing the sample into a syringe, attaching a VST filter and pressure filtering the sample, then allowing it cool to room temperature. Further, I calibrate the VST with distilled water between each sample.
Filtering is controversial. VST recommends filtering
, and it results in lower TDS readings. Some notable persons recommend skip it, and there are threads on it. However, I find it to be useful for consistent readings and can be used to compare various brewing methods.
Unfiltered refractometer measurements are higher than filtered.
I measured two of my typical morning espressos and then did 3 more with different parameters to see how the extraction proceeded. I also tasted each hot, partially cooled (recommended) and well cooled to room temperature of about 68f.
Data and calculated value table:
My preference is for the smaller shots with TDS around 10% with this coffee. It is denser and the flavors are very good, nicely balanced with EY ranging from 17.5% - 18%.
All the shots were good though, none exhibited over-extracted flavors. Had slight channeling on the 36g dose. The very long shot of 54g (~1:3) was very fruity and juicy, with no bitterness or harsh flavors and lots of clarity. However, I don't particularly care for the body at the density it produced. It ran for 38 seconds.
So honestly, with the Monolith Conical, the LMLM and a light roast ethiopian, I was able to pull over 22.24% E.Y. with good results and no particular effort on my part, other than just dialing the grinder a little bit.