Differences in solubility among coffees

I’m currently sipping on a cup of Sweet Bloom’s roast of Thageini from Nyeri, Kenya, which according to my calculations with my Atago PAL-COFFEE refractometer, I extracted to 23%.

I used Matt’s V60 recipe, and his coffee brewing water recipe, taken from here. In his brew instruction video, Matt says this recipe ended up giving him 20.8% extraction (1.40 TDS). The v60 recipe is as follows:

12g coffee
200g water
water at 97c (I used water just off of a rolling boil)
50g bloom, 50g water after 30s, 100g after 60s, finish time 2:20.
I also put the kettle back on the boiler in between pours.

I finally nailed the finish time, and my pour has been improving, but this level of extraction is still shocking. Like I said, my coffee is at 23% extraction (1.60 TDS with this recipe). However, I measured the cup I made yesterday and the TDS was even higher, around 1.64. I thought my refractometer wasn’t calibrated correctly, because this came out to an extraction of around 24%, but lo and behold, distilled water tested at 0.00% and I let the coffee cool completely before testing. The flavors are incredible by the way, lots of sweetness, and I don’t taste much, if any, overextraction.

What could be different about this coffee I’m drinking now that leads to such a high extraction? What factors could be affecting the solubility this much?

It sounds like a complicated science project.

Sounds complicated but takes seconds to do if you work in to your routine, in between waiting for kettle to boil, rinse brewer etc. It’s just expressing a few drops of coffee from a pipette then pressing a button, actually brewing the coffee is much more complex & time consuming :slight_smile:

In answer to the OP, I frequently find Kenyans to extract more than a lot of other origins (same grind setting & recipe) & still taste delicious at the higher margins of the Gold Cup box. In contrast, Costa Rican honeys are often at the lower end, but can still be very tasty. I generally aim to have a number of different origins average around 20% & don’t fret if some fall a % or two either side of this…as long as they still taste good, of course.

Soluble solids in roasted coffees have been seen to vary by more than +/-10%, so it seems perfectly reasonable to assume that what you can extract in the cup (all else being equal) could vary by a similar margin.

1 Like

I’ve found that you have to put a cup upsidedown over the eye of the Atago refractometer to get anywhere near consistent results. This should block out any ambient overhead light that may interfere with your reading and essentially mimics the vst lid. Also, if you don’t take readings at a consistent temperature every time, you will find that the readings with vary by quite a bit. Hope this helps!

The roasting process turns largely insoluble green coffee into soluble brown coffee. Different roast profiles will affect how pronounced this effect is.

Atago also sells a metal combination cover/heatsink that I like to use.