Hi all,

I have a Mahlkönig Vario with steel burrs (calibrated to have burrs touching at about 1M). Most of the coffees brewed taste good around 18-19.5% on the VST Refractometer. From what I know, this makes sense given the level of the grinder.

I'm currently drinking James Gourmet's Guatemala Coban Finca Santa Sofia (http://jamesgourmetcoffee.com/product/g ... r-profile/) roasted 10 days ago (degassed 7 days before drinking). I have never encountered a coffee like this: I can't get the coffee in the 18-19% zone as it extracts so readily.

These are from memory but fairly accurate:

Recipe 1:

V60-01
18g coffee (ground between 3-4 on the Vario)
266g water (Waitrose Essential) @ 90°c
35s bloom with 3 subsequent pours to 266g water

VST aim:

266g brew water
231g beverage weight
18% extraction
1.40 TDS

Result:

The coffee is passing through my V60 in under 2 minutes (finishing pouring water around 1'30 - 1'45). End result is about 1.75 TDS is around 21.5% and unpleasant.

I've had my refractometer about 7 months and the interesting part is that the VST app is always accurate to within ± 2g on the beverage weight prediction. With this coffee it is around 10-15g below the prediction. Why?

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Recipe 2:

Kalita Wave 155
18g coffee (ground at 8A on the Vario)
266g water (Waitrose Essential) @ 90°c
30s bloom with several pulse pours to 266g water

VST aim:

266g brew water
231g beverage weight
18% extraction
1.40 TDS

Result:

Easily finished pouring by 2 minutes as draining very quickly. End result around 22% and unpleasant.

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Recipe 3:

Same as Recipe 2 but with 21g coffee / 266g brew water @ 85°c. Got the brew down to 19.57% extraction which was too acidic with no sweetness and none of the normal fruit flavours.

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Also tried an Aeropress ground at 4A brewed for only 50 seconds (with 50g water @ 85°c/30s bloom/3 stirs) and plunged for further 20s which came out at over 23.5% extraction and obviously disgusting!

So what's the deal? Up until now I've been hung up on extraction numbers (18-19%) because they've always been in accordance with what I've read about grinding. Now I'm confused and bewildered by this coffee's extraction and the fact that it probably tastes best around 20.5%. Why does it extract so quickly with a coarse grind? Is this coffee best suited to immersion brewing instead? Am I being an idiot somewhere along the line? Should I stop being so hung up on numbers?

Numbers are great things to keep track of, you're lucky to be able to get so in depth with your coffee making with the refractometer.

Have you tried to re-calibrate your refractometer with some de-ionised water?
Do you clean with alcohol wipes or try putting isopropyl alcohol in an atomiser and wipe with some dust-free tissues?
Are you using the syringe filters?

I have Vario / Steel burrs.

With light to medium / light roasts that are well developed and quite soluble, I generally find myself consistently enjoying the best cups in the 20 to 21% range. Sometimes with a super light roast I can push up to 21.5%.
TDS readings are 1.35 to 1.42, with CO2 and moisture set to zero. LRR default 2.10
brewing 58 to 65 g / L for V60 1 and 2.

1 cup brew times are usually around the 2 - 2:20 mark total using 12 to 13g coffee. In my experience dosing anymore than this becomes problematic and results in uneven extractions.

2 cup around 3 - 3:20 using 28 to 32g coffee.

Water is around 100ppm GH / 40ppm KH

I will also add, I may be just reading you wrong though? Do not chase the numbers... brew it up, mix it up, set a small amount to the side, taste a small amount of the coffee first, keep tasting as the initial heat drops off, assess, then check the numbers.