MWJB The device works OK, but that video is wrong/poorly translated.
I did wonder, but there was a reason my ears pricked up when I hear brew water.
It got me thinking, because I know refractometers are calibrated to zero using distilled. Which makes sense in a chemistry lab (I used them when I did my degree). This was because everything you did was dissolved in distilled/deionised water. So every change you measured was purely due to what dissolved within that water and the math always closely match the reading expected vs the actual reading. So distilled water absolutely made sense.
Then we come to coffee…we calibrate in distilled, then use water with some TDS to actually make the coffee. When we measure we are really measuring the dissolved coffee + the brew water. So any extraction yield calculation, must logically not really be extraction yield.
It would seem we should if using the accepted methods:
- zero with pure water
- measure RI of brew water
- measure RI of coffee
- Perform a calculation RI coffee - RI brew = true RI. And from this calculate true extraction yield.
Or am I missing something fundamental, doesn’t it make sense to use brew water and not have to worry about the last point?
I just had a search and the question comes up here as well
