gyro wrote:I'm reasonably confident on the ROBUR-E that purging fully clears the chute. I run it with the top off and it certainly appears to come out in an even manner, and then get diced up by the static grid. What I am less sure of, is what happens in the burr chamber, ie after the burrs has spat it out, but before it enters the chute. So while I say I'm fairly confident that the chute is purged of the grinds that were in there, I am not implying that they are necessarily replaced with the freshest ones that were just ground. It seems very likely there will be mixing of the grounds that are yet to enter the chute, but were previously ground.
Indeed, Chris, Paul and I were discussing this recently. When his grinder is freshly cleaned and then filled up, the chute seems to clear fully, i.e. all the sections of static grid eke out coffee. However, we noticed that sometimes, this would stop, and the top 2 sections would purge much more slowly than the bottom 4. Paul just noticed this recently and showed me, so I don't know what causes that, how to fix it, or what, but it was present on his properly functioning grinder at 60 Hz with ~3s, 17g shots.
gyro wrote:Interestingly, I've been out of the country for a few days and just made a few coffees this morning. First double as a seasoner, then next to drink. This is the first time since I've had the new grinder (in a working fashion) whereby it hasn't been used daily. My second and third shots weren't up to the usual standard today, and I wonder if this is the reason... guess I better go and have another in the interest of research
This is the problem that Paul has been having for a year or so with his Robur E/ Synesso setup, which he's demoed for me several times that I've visited. The first shot is a "seasoning shot" for him, and he's fine with that... It always pours thin as you mentioned, and is a full-on sink shot. The problem is, the second and third shots are also "off" in the same way. They usually pour much better, visually, but they have a notable bitterness. They aren't sink shots, usually, but they're not up to par. When you make that 4th shot, you realize that the previous two were rubbish by comparison: with the same coffee, and no adjustments, it's always better-balanced and noticeably sweeter.
For what it's worth, Paul's job is such that he is away from home several days a week, so he routinely comes back after a multi-day absence. I am not sure if he leaves coffee in the hopper during that time or not, though, and, also for what it's worth, he's not completely sure that the grinder is the problem, although we both suspect so. Fingers crossed he'll chime in at some point; I know we're finally talking about something close to his heart...
gyro wrote:Ok, so I thought that now the burrs have settled in a bit, I would get an accurate idea of how much grind retention there is in the ROBUR-E. So I ran it until the hopper was empty and no more coffee was exiting the chute.
Here is the coffee retention in the chamber before reaching the chute. For one reason or another, while the grinder is running this residual coffee doesn't enter the chute. Perhaps on the 60Hz version there might be a little less since its spinning faster?
However, there was much less than I thought. Emptying it all and weighing it, resulted in only 14 grams of coffee. Not an insignificant amount, but less than I had thought.
I believe when purging the stale coffee first thing in the morning, all the grounds in the chute are expelled, but who knows regarding the stale grounds in the chamber itself.
If I may critique your experiment: I don't think that emptying the hopper by grinding it till empty will give you a good picture of how much is retained; I think you need to fill the hopper, grind until the system is "full" as usual, and then shut the hopper gate, take off the hopper, scoop out the whole beans on top of the burrs (say, with a vacuum cleaner), and then remove the upper burr assembly. I suspect that running it empty will yield less "held up" coffee than there actually is when you keep the hopper full. I bet you're right that it's closer to 20 grams than the 40 I was guessing, but, as I said, the issue is both the amount of stale retained and the rate at which it "bleeds in" to the fresh ground coffee, tempered by the "detectability" threshold, i.e. what ratio of stale coffee to fresh coffee in the cup is detectable to your palate. Paul's taste experience suggests that it's detectable as a defect in the coffee for three shots. I've experienced that 3-4 times; I am sure he's experienced it 50-100+ times...
Anyway, on that note, it's worth throwing in this comment from Jim
in One Shot Grind Remnants:
another_jim wrote:Take a coffee, grind a few grams, put it away for a day. Then brew two cups of coffee fresh ground, and one with 20 percent of the day old ground. Pick out the odd cup. For most people, 20% to 25% will be the low limit of being reliable on this exercise.
Anyway, that's my current take on the issue of staleness/waste on the big Mazzer E grinders. It makes me wonder if the Major E might have less retention owing to how fast its burrs and sweepers spin (3-4x the speed of conicals)--I expect there's a reasonable chance that it throws out the stale grinds faster because of that. WAG, of course.