VST Labs Coffee Refractometer & App

How much of the coffee you ground has been sucked up by hot water and arrived in your cup to taste? Is it the considered optimum of 20%? You can bake your puck and weigh it later to guess, but you could measure it too and use a coffee cockpit of slides and gauges to navigate your next cup.

Here's a video by Matt Perger:

At the Coffee Company they also use a VST refractometer and the App from VST Labs to measure this:  (below is a snapshot from https://vimeo.com/84681146 )

We got one from the VST labs and did some first measurements. Turns out a cup we like, made with 15g of ground coffee beans, extracted 25g in 40 seconds on the lever machine, gave 8.8% TDS which is a bit low. Within the targeted Coffee Brew Formula but too weak on the given chart.

There's more to try with grind setting and dose to define the optimal mix of variables!

Espresso cooling

Filtered (right) through filter head on syringe (left)

Drops on the eye of the TDS, below the blue lid

Measures 8.8% TDS, a bit low on the green line in the Brewing Contro Chart on the iPad app

On the Home-Barista forum, I received some good advice from several different members:

Dick Green wrote:

Freshly-roasted beans may under-extract. That's because the beans are still outgassing and the CO2 interferes with extraction. You can test this by grinding a couple of doses, pulling one of the doses and measuring extraction yield, then holding the other dose in a plastic bag for a few hours, then pulling and measuring the extraction yield. Grinding will dramatically increase the rate of outgassing, so after a few hours you may be able to get higher extraction yields (though the cup may not taste as good.)

If you're pulling light-roasted beans, you may not be able to push the extraction yield beyond a certain point even if the beans have fully outgassed.

Bryan Truitt wrote:

If you liked the taste, it isn't under-extracted. 'under-extracted' is a qualitative description than can correlate to a range of extraction yields under certain brewing conditions. The coffee brewing control chart is a good reference but should only be a starting point for evaluation based on taste. For me, 20% tastes under-extracted on an Mahlkoenig EK43 grinder, not a Baratza Virtuoso. The quality of coffee and degree of roast also matters.

Longer flow will increase your extraction yield. The % TDS will go down. The calculation for the extraction yield is dependent on the measured beverage [...]. You can also increase yields for a given beverage size by grinding finer. Grind quality will often put an upper limit on the yields you can achieve for short shots—at a certain fineness your yields will go down.

Switching to fresher beans will lower extraction yields. Switching grinders changes which average extraction yields taste good by shifting the particle size distribution and extraction evenness.

Forget any expectations for brew time and just measure weights. Use good distribution technique and taste your shots at various yields and strengths and compare them. Experiment with much longer shots, like 36 or 72 grams. And don't be afraid to let short shots take more time than you are used to. For 'filter coffee' people often have very specific preferences for the strength of their beverage. The strength of the beverage which comes out of an 'espresso machine' is different at every cafe (unfortunately often within the same cafe). I have seen anything from 1.38% TDS to 20% TDS.
I like the idea of taking the freedom to vary and experiment, taste and then also measure the outcome.

On his blog Matt Perger posts a number of recipes on the espresso machine that vary wildly in TDS and extraction value. Some coffee is much more like filter coffee than typical espresso:

"Espresso Course –
Red Bourbon, Roasted on the lighter side of traditional espresso.
21g dose, 48g yield, 27 seconds, 9.5% TDS, 21.7% extraction.

Cappuccino Course -

Red Bourbon, Roasted with slightly more development and similar end temp.
21g dose, 50g yield, 27 seconds, 9% TDS, 21.4% extraction.

Signature Drink -

Espresso Component – Same as espresso course

Allongé – Bourbon, roasted slightly lighter and faster than the espresso.
20g dose, 100g yield, 25 seconds, 4.5% TDS, 22.5% extraction.

Lungo – Caturra, roasted halfway between traditional filter and espresso roasts.
19g dose, 150g yield, 25 seconds, 2.9% TDS, 22.9% extraction.

Coffee Shot – Geisha, roasted lightly, as we would usually for filter coffee.
18g dose, 300g yield, 30 seconds, 1.4% TDS, 23.3% extraction.

All of these extractions were very deliberate, and tuned for each roast style and strength of drink."
(He served these during the 2013 Championships: http://www.youtube.com/watch?v=ZgKgt2gtzD0)

Next I pulled & measured an Ethiopia Amaro Gayo that I find delicious in the cup, despite some passing sense of dryness. A pleasant mix of tastes that I find hard to describe so I won't delve deep to try it.

About one percent lower extraction-% and %TDS.

 Next, I tried the delicious Panama, Los Lajones beans on the Mahlkönig Vario grinder and the Rocket E61 machine, using 20g in the 20g-VST basket to brew 31.3g of espresso. This machine has a dual OPV so I could ramp up the pre-infusion at 4 bar, first drops appearing at 6 seconds, then up to 9 bar for 6 seconds and extracting the rest at 4 bar again.

A delightful, somewhat 'salty' taste:
Another photo impression of a measurement session:

Setup, with the Tonino that I use to measure the color of the grinds before the extraction:
 Half of the espresso to taste and half of it in a big cool cup to cool down

 Filtered espresso in the small heavy shot glass, taken out with pipette, drops on the refractometer:

Measurement done, ready to copy into the app

At Trakteren, a local coffee specialty place, I was invited to demo the setup and we did two measurements:

At home, I tried several extractions with Ethiopian "Cherry Red" beans that I roasted three weeks ago. At 16-17 % extractions these taste rich and spicy, like Dutch "speculaas" dipped in coffee, almond candy, and at slightly lower extractions it's a soft, light espresso. Both very enjoyable even though all of these were at lower extractions than the "box" of the app would have you expect.


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