Has anyone done some controlled, A-B comparisons of how and how much retained grounds affect the cup (immediately, and build-up over time)? I'm coming off an HG One thread, and it seems like even with observationally "low" retention, people still find the HG One's retention something to discuss (maybe since everything else has been discussed a zillion times ) I'm not asking about whether there's retention, but how much before you can taste it?

Of course, retention is a more general issue. Whether a couple of grams remain for a day or "pollute" a different bean seems obvious. A filthy grinder is a bad idea even if it can't be tasted it in the shots. However, when I've opened up and brushed out my Vario, I didn't find much and can't imagine detectable taste effects. My Mazzer Mini requires a brush out after each shot; but even with the Mini, I've never noticed a positive change after cleaning out the packed-in grounds around the burrs.

So whassup?

Well if not psychosematic or not I find a clean grinder to have less bitterness and off tastes.

Also more practically speaking, retention makes changing grinds / coffees waste as you have to push whatever amount of retention through. In MM case was more like 20-30g, so switching coffees was wasteful. Done with the sweeping thing after 15 years, finally.

Delicate SO coffees get muddy in unclean grinders I find. Traditional "slammer" blends probably won't notice.

I guess it's one of those things where it doesn't directly affect but is another variable under control. Me once you get into non-traditional grinders HG One / VL you can't go back.

Martin wrote:Has anyone done some controlled, A-B comparisons of how and how much retained grounds affect the cup (immediately, and build-up over time)?

Not "controlled" in the scientific sense, but over the years I have found concern about minor grounds retention to be highly overstated. There really is no need to go OCD about it.

With the Vario that I used to own, I definitely noticed a perceptible quality difference in the first shot of the day between when I purged a few grams and when I didn't. I usually didn't bother purging between shots in a session, though.

With the HG-one, it is mainly just OCD, as I doubt a few tenths of a gram would make a tastable difference. But I like the purity of putting an exactly weighed dose into the grinder, and getting all of it back out to use for a shot.

If it effects the flow rate, it effects the taste and my nerves.

I believe retention only affects taste in a significant way when more than a token amount of stale grinds or grinds from a different coffee mixes into the current dose. The thresholds for amount, staleness and difference probably vary considerably depending on the coffee(s) involved, the preparation parameters and the person doing the tasting. But I imagine that most of us could detect a gram or two of very stale/different coffee mixed in with the current dose. Below that level, I'm skeptical unless the retained grounds have become rancid.

So, if your grinder has a lot of retention, as is commonly the case when a hopper is used, and/or the grind path is long and/or the chute is not easily accessible, it's a problem. In such a configuration, several grams of coffee can be retained (levels as high as 10g have been reported), and I have no doubt this will affect taste if the coffee is stale and/or different from the coffee you're pulling. In that case, retention is a very big deal.

Grinders like the Vario, the Pro-M and Versalab M3 with hopper significantly reduce retention by having a short grind path and a chute that essentially points straight down (or have no chute at all, as in the case of the M3.) But as long as a hopper is used, you still have to get rid of the grounds and partially ground (or stuck) beans in the burr chamber if they've been sitting there for a while or when you switch coffees. But the burr chambers aren't very large and I suspect the retention for these grinders when used with a hopper may be on the borderline of what you can taste, again unless the grinds have become rancid. It would be interesting to run some experiments on that.

Of course, if you single dose, you can run and/or pulse the grinder until the burr chamber is reasonable clear of grinds that could mix into the next shot (grinds that have stuck to the walls of the burr chamber will stay there and not mix.) The chute design generally dictates whether you can brush out the grinds that remain in the chute. Some grinders let you get a brush deeply inside, others don't. Some of the doserless models make it very difficult to get all the grinds out of the chute. I believe in those cases the amount of retention can be significant, and therefore the taste will be affected. The Vario is an exception because the chute is quite short and points almost straight down from the burr chamber. Generally, you can run or pulse the grinder to get rid of most of the retained grinds instead of having to use a brush. The Versalab M3 without a hopper and HG One are essentially chute-less single-dose grinders, so retention is pretty-much nil and I very much doubt that even the small amount of grounds that stick to the burrs after grinding will have any noticable effect on taste.

FWIW, I single dose and always pulse my K10 and brush out the chute as part of grinding the current dose. If I didn't do that, a large amount of grinds would remain in the burr chamber and chute -- probably on the order of 5g or more. That would mix into the next dose, so if the retained grinds get stale or rancid, or I switch coffees, I'm going to taste them. In that case, retention would be a big deal.

Unfortunately, my OCD has never manifested itself in tidyness I only wish.

I single dose, I run a brush over what I see, and would just as soon not frequently dismantle burrs looking for buildup. I'm mindful of certain ritual behaviors that can't be (are not worth) empirical testing, but collectively might add up to a difference. Looks like I'll be keeping my Vario and new HG One on the counter (finding a new home for my Mini)--addressing most bean switching and grounds retention issues with a shiny new machine. Thanks for confirming that this is a pretty good (if not the most economical) approach.

One reason to pass on the HG-One.
My Rosco Mini does not show any retention, other than left on the bottom of the grinder that I brush off with my finger into the PF basket.

That sounds like the hg one to me. Not to mention that Rosco has the 38 burrs

insatiableOne wrote:One reason to pass on the HG-One.

There's never a shortage of reasons to pass on any piece of coffee gear.

I was curious whether among reputedly low-retention grinders (ex., Vario, HG One, and OK, Rosco,) folks could actually detect cup differences between keeping the works immaculate and, at most, a quick brush or blow. Seems not.