V60: Drip or Immersion on VST Coffee Tools?

 

Drip, dah! Obvious right? well maybe not.

If you are using a “traditional” technique that calls for staged pours, maybe 50g at a time, then Drip setting will give you the most accurate EXT %. However things are a little more complicated in my experience if you are using a technique advocated by Scott Rao and the likes of Matt Perger (watch video here). This technique in contras involves a small “pre wet” followed by the rest of the water dispensed in one complete pour.

Why the difference?

Well it all comes down to assumptions the app makes regarding the nature of the liquid retained by the coffee bed. With traditional drip coffee, fresh water is always passing through the bed and if one was to measure the liquid coming out of a V60 at the end of a brew, say the last 10g, it would have a very low TDS. It can be assumed then that the liquid retained by the bed is just water and can be discounted. Any calculations need only take into account the Dissolved Solids in the cup.

In a full immersion brew, lets take a plunger, after 5 minutes if one was to pour out the plunger and take a measurement, we’d have to consider not only the liquid in the cup but also the liquid retained by the bed. Why? Well, because the grounds were in contact with the brewed coffee so the liquid in the bed would be saturated with the same amount of dissolved solids (as a %) as the cup.

Lets break this down and take a look at the maths behind the VST App. Below is an example of a V60 using Drip and a Plunger using Immersion. The Liquid Retained Ratio (LRR) is left as the app default, C02 and MOIST are “0” to make the math simpler for this demonstration.

VST APPS for Android
Presets: LRR = Default, CO2=0, MOIST=0
V60
Dose (g) 12 From Scale
Beverage Weight (g) 200 From Scale
Cup
TDS % 1.25% Refractometer
TDS (g) 2.50 1.25% x 200g
EXT % 20.83% 2.5g/12g
Liquid Retained
Liquid Retained Ratio 2.10 Assumed by App
Liquid Retained (g) 25 2.1 x 12g
TDS% of LR 0.00% Assumed by App
TDS (g) of LR 0.0000 1.25% x 30g
EXT% 0.00% 0g/12g
Combined TDS (g) 2.50 2.5g + 0g
Total EXT% 20.83% 20.83%+0%
PLUNGER
Dose (g) 12 From Scale
Beverage Weight (g) 200 From Scale
Cup
TDS % 1.25% Refractometer
TDS (g) 2.50 1.25% x 200g
EXT % 20.83% 2.5g/12g
Liquid Retained
Liquid Retained Ratio 2.50 Assumed by App
Liquid Retained (g) 30 2.5 x 12g
TDS% of LR 1.25% Assumed by App
TDS (g) of LR 0.375 1.25% x 30g
EXT % 3.13% 0.375g/12g
Combined TDS (g) 2.875 2.5g + 0.375g
Total EXT % 23.96% 2.875g/12g
So back to the “Rao Method”*, in recent experiments it was found that the liquid that is coming out at the end of the V60 is of a concentration very near to the concentration of the cup. Here is an example of our readings below.

RAO METHOD
Dose (g) 12
Beverage Weight (g) 200
Cup
TDS % 1.25%
TDS (g) 2.50
EXT % 20.83%
Liquid Retained
Liquid Retained Ratio 2.50
Liquid Retained (g) 30
TDS% of LR 1.02%
TDS (g) of LR 0.306
EXT % 2.55%
Combined TDS (g) 2.806
Total EXT % 23.38%
This means we are much closer to immersion than drip ie 23.38 compared to 23.96.
So what now? Well we can hack the system slightly by adjusting the LRR. If we run a liquid retained ration of 2.04 it will give us the same reading we get manually so or our particular method it gives us an accurate indication of the Extraction Yield**.
Has anyone else had conflicting experience? Feel free to question my numbers, happy to be shown i’m wrong if that happens to be the case.
*My name not his

** How does this work? The TDS of the liquid retained in our V60 was 0.306g rather than 0.375g on the Immersion example. This is 81.6% (0.306/0.375g*100). So if we can take the default Liquid Retained Ratio of  2.5 for Immersion and scale it down to 81.6% of its value we get 2.04. So if we adjust the LRR to 2.04 instead of 2.5 on Immersion, this will do the job of tricking the app to say the bed now only retains 0.306g of coffee.

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