Hello,
I'm trying to establish a correct formula for calculating the extraction yield (EXT) for pour-over methods of coffee preparation as I don't have enough money to buy VST refractometer and don't like to spend money on their software either (their patent claims aimed at netphilosopher on coffeegeek made me more than angry).
I live in Europe (and this server is located in the UK AFAIK) so these patents can not have any effect on us at all, however if doubt please move this whole post to the members-only area.
Currently I think I have nailed some "basic" stuff - I can calculate EXT from known value of TDS (obtained by drying a 50 g sample of the beverage and weighing it on 0,01 g scale) Dose and Beverage Weight.
Now it's time to gather enough test data and try to obtain correct approximate formula including side effects such as CO2 and Moisture content in Dose.
The equations accounting for Brew Water and Liquid Retained Ratio seems bit overcomplicated (actual measurements show values of 2,3-2,4 for LRR) and not so precise as exact measurement of just the Beverage weight so I will ignore that matter for now.
please see the attached image, but in any case:
EXT = TDS * DOSE / BEV