samuellaw178 wrote:I forgot to measure the TDS of the first shot (I have an Atago refractometer). So I did another shot using the same procedure. Ended up with 12.4g for the shot. So the process is repeatable, good news. The 12.5g dose was pulled into 31.6g in about 27s. Was a tad too long I realized afterwards. Again, I've got the creamy mouthfeel and the lingering after taste. Measured the TDS and calculated the EY%. Guess what?? The TDS came at 8.1%, but the extraction yield was 23.8%! Never had I gotten such high EY even with overextraction. It does taste slightly overextracted but is drinkable. I will have to cut back the shot volume next time, or use more grind.
12.5gr coffee to 31.6 grams beverage at 8.1% measured TDS comes to an EY of 21.22% (VST CoffeeTools). How did you get to 23.8%?
NB - I wonder if your assessment of the boulders may be the difference between grinders. If you are correct then in theory, assuming you have 10% boulders in your dose, your "boulder-less equivalent" dose (as entered into the EBF or EY calculation) should be 10% less than the measured dose. At which point EY would rise.
So assuming the 12.5gr coffee has about 10% boulders: 12.5gr - 1.25gr = 11.25gr
Recalculating EY for a dose of 11.25gr --> EY = 23.68%
That is a full 2.46% - quite an error!!
So a separate hypothesis is that for better grinders: [dose] = ["boulder-less" equivalent dose].
NB - What this means is that, for a lesser grinder, a larger doses may "over extract" rather than "under extract" - even though the Refractometer will say otherwise - since the part of the dose that actually participated in the pull (the "not-boulders") was lower than the measured dose. The hypothesis also renders a VST plot without sifting almost useless for anything but a perfect grinder.
Edit: BTW - Testing the hypothesis that boulders do not participate in the pull should be fairly easy. Grind two doses and sieve the boulders from one. Run the same beverage weight from both. If the TDS is identical (or nearly so) means the boulders did not participate in the percolation. (unfortunately I do not own a sieve so can't run this test myself).
Scraping away (slowly) at the tyranny of biases and dogma.