Comments similar to the following appear every then and now.

Sherman wrote:Popcorning can be mitigated by placing a tamper, backflush insert, or other similarly fitting device in the throat, on top of the beans.

Since replacing the burrs in the MC4, I've been experimenting with varying effective bean columns above the burrs. On both the MC4 and MXK, using a timer, the doses are more consistent AND, more importantly, the taste is more balanced when the bean effective bean column height is about the mid point of the standard hopper. As the bean column shrinks, the dose becomes more erratic and shot consistency suffers. Bitter flavors are too prevalent, blonding can be hairtrigger and shots tend toward the thin. Adjusting the dose to ±0.1g does not mitigate the defects.

With a heavy weight like a tamper, shots tend toward the muddy and flat.

The math:
Typical 57mm tampers range from around 300 to 500 grams. Coffee weighs about 20g per inch in a 57mm diameter, so the effective bean column height is 15 to 25 inches, much higher, and heavier, than beans in a hopper.

For the MC4, a small water bottle with about 75g works well. For the MXK, with its conical burrs, about 150g.

Note : I always purge the grinder for a second before grinding the dose. These are impressions only on e61s pulling medium roast, moderate ristretto, low dose, mid temp singles, and as always YMMV.

I use one of those cheapy aluminum ones. I guess it is time to weigh it.

I'm not sold.

In the Mazzer and Compak, the tamper sits above the level of the beans, resting on protrusions in the Mazzer or the burr spindle on the Compak, for almost the entire shot. On those grinders, the tamper acts as a lid, not a weight.

The effect of popcorning is to reduce the number of beans that feed into the burrs in a given time interval. This means less of the grinding action is bean to bean, and more bean to burr. This in turn means you need to adjust the burrs more closely for the same grind fineness (i.e. the same number of breaks per bean).

So if your tamper is overweighting the beans, the grind would be coarser than that of a filled hopper.

The weight of the device notwithstanding, anything that can effectively span the diameter of the grinder throat will suffice as a lid. I don't claim to have run exhaustive tests on different weights, but can relay from personal experience that I've used everything from the palm of my hand, an empty yogurt container, tampers, to empty pf baskets and hopper lids and have not noticed the difference in flavors that Ian has listed. I have noticed a significant difference in countertop cleanliness, however .

That said, my caveat is that this works on my specific equipment. I posit that this may be specific to grinder/machine/bean combos, and encourage any interested parties to explore the matrices of possibilities. Based on my experience thus far, I haven't noticed a significant difference in using different anti-popcorning devices, regardless of the beans used.

-s.

another_jim wrote:In the Mazzer and Compak, the tamper sits above the level of the beans, resting on protrusions in the Mazzer or the burr spindle on the Compak, for almost the entire shot. On those grinders, the tamper acts as a lid, not a weight.

Interesting point. However, this does assume grinding per shot.

Then again, the SJ throat is tapered in, right where the protusions jut out (I believe that these act as resting points for the hopper, so that it's not held in place by friction between the conical section of the hopper and the throat). If you were to use a device whose diameter was appropriate to clear only the tapered section of the throat, there would be enough of a gap between the device and the throat sidewall that beans could get stuck.

The red circle contains a threaded hole. The hopper has a corresponding hole, and when assembled, there is a screw that helps to keep the hopper from rotating.

-s.

I sold my Mazzers a year ago but if I remember correctly one shot worth of beans sit about even with the inside tabs or the shelf above the burrs. In that case, the tamper does nothing but provide a lid. The tamp will not be setting on the beans. They will all be in the inner void above the burrs or if it does physically sit on the bean column, it is only there for a few seconds possibly about 1/3 of the grind time. Every grinder is different and I have not had a Mazzer for a while so take it with a grain of salt. On my Cimbali's, I just keep 4 or 5 shots worth of beans in the hopper.

another_jim wrote:The effect of popcorning is to reduce the number of beans that feed into the burrs in a given time interval. This means less of the grinding action is bean to bean, and more bean to burr. This in turn means you need to adjust the burrs more closely for the same grind fineness (i.e. the same number of breaks per bean)

Don't you think the distribution would change? That's how it tastes.

With a light load, the beans are bouncing like ping pong balls getting bits knocked off willy-nilly with relatively less fine production. One has to grind finer, to limit the size of 'chunks' slipping between the flats, or user more coffee.

With an optimum load, the beans are fed into the maw and the blades work as designed generating fines and 'chunks' in balance.

With an overload, the beans are forced into the maw and the blades smash into more restricted beans and force bean into bean, generating more fines per bean. One has to grind coarser or use less coffee.

I realize my explanation is a trifle simplistic. If something else is in play, elucidate me.

Hmm.. pressure transducer in the hopper's throat. Screw top hopper lid... inflatable bladder attached under lid... small air pump incorporated in lid's handle... all hooked to a PID to maintain constant force on beans as the volume decreases... Is Jim Gault listening...??

I would agree with cafeIKE here. My experience is that when changing from grinding single doses (without any weight) to having at least few doubles worth of beans in the hopper I could make the grind setting quite a bit coarser. My current espresso fineness area stops where it used to start (on Mini-E).

I haven't compared these two methods side by side, but have heard of at least one guy who did it on Rocky and noticed that having no weight made extractions run quite a bit faster.

From my experience (at least on conicals), less weight on the beans results in a coarser grind. I keep a small weight of beans in the hopper, and I can even notice the courser grind visually before the shot confirms it if I have neglected to replenish the hopper and its starting to run low. I also suspect its to do with the feed rate change. On the few occasions where I have actually filled the hopper, I have noticed more coffee in the basket for the same grind and grind time than with my 'normal' (albeit small) bean weight.

Cheers, Chris

One of the unsung advantages of the Cimbali Max is the tube built into the hopper, which allows you to maintain a column of beans above the throat of the grinder.

I postulated the very same in La Cimbali : Finger Guard or Bean Mass Regulator

+1. Large commercial grinders are obviously designed to be operated with a large mass of beans above the burrs, but that's impractical for home use. My solution is to use a mini-hopper filled with several shots worth of beans (at least 50g, preferably more). I've found that grinding time and extraction characteristics begin to vary significantly when the bean mass drops any lower than this. Like Ian, I don't believe that using a tamper eliminates this problem.

It would be interesting to run particle size distributions on the grinds from the last, say, 5 shots as the hopper empties, and try to quantify these observations. Maybe someday...

I'm mystified by the constant repetition of this non sequitur. Of course, the grind and flow changes as the hopper empties. Of course, the taste will be worse if you don't make the required adjustments.

This proves nothing about single dosed shots, since these shots do have the proper adjustments.

When this issue first came up, I compared shots side by side single dosed and from a full hopper on my Compak, and on some of the Titans, and on the Vario, when they were here. In these comparisons, I did make the required adjustments. I could taste no consistent short term difference between the shots.

As far as I can tell, the only thing this observation of different hopper fills or tamper pressures proves is that if you don't adjust the grind and dose properly, shots are worse. In fact, your observations actually are an endorsement of single dosing. When I single dose, the grinder is in an identical state every single shot. If you don't refill the hopper to the same weight after each shot, your grinders are not the same state, and the grind adjustment/dose drifts further and further from optimal with each shot.

another_jim wrote:This proves nothing about single dosed shots, since these shots do have the proper adjustments.

Are you sure that the effect can be completely reversed by changing the grind setting? Because what we are saying here is not that the average coarseness varies, but instead the distribution of different particle sizes. You get more fines with weight on beans. Depending on your grinder it is either a good thing or a bad thing, but more often good I suppose.

When I single dosed the Mini-E, the grind setting needed to be fine and it caused occasional blocking of the anti-static grid. With timed dosing I don't get that any more. So maybe the grinds are not identical, but on average coarser with additional fines so that pour times are identical.

If you don't refill the hopper to the same weight after each shot, your grinders are not the same state, and the grind adjustment/dose drifts further and further from optimal with each shot.

Actually it happened right after I read the original post of this thread and went to brew an espresso. Yesterday the shot had poured a bit too slowly, so I had dialled the grinder a bit coarser. To my surprise, there was no flow. So the effect of dialling the grinder was reversed. Then I realised that I had poured the rest of the bean bag into hopper and it had such a major effect.

I find myself dialling the grinder as the hopper empties. I have contributed this to beans getting older and losing moisture, but it might actually be mostly about the hopper getting empty.

Are you sure that the effect can be completely reversed by changing the grind setting?

Effect? Reverse? Do you mean can the ill effects of filling the hopper be reversed by setting the grind coarser, or the ill effects of emptying the hopper by setting it finer?

When there's no systematic taste difference, there's no effect, and nothing to reverse.

Effect? Reverse? Do you mean can the ill effects of filling the hopper be reversed by setting the grind coarser, or the ill effects of emptying the hopper by setting it finer?

Both. Can the weight on beans (or lack of it) be fully compensated with changing the grind setting?

When there's no systematic taste difference, there's no effect, and nothing to reverse.

It might well be. cafeIKE argued that there is a systematic taste difference, but I guess no one has comprehensively tested it.

I single-dose grind doubles with my major and I can confirm that 20g of beans just reaches the top of the bottom burr spindle, and the tamper doesn't get anywhere near that because of the taper of the throat. All it does is stop chunks of bean being spat out across my kitchen.

another_jim wrote:Of course, the grind and flow changes as the hopper empties. Of course, the taste will be worse if you don't make the required adjustments.

Jim, rest assured that I understand. Of course I'm talking about properly adjusted grind settings. The question is, even when the grind setting has been properly adjusted to the same flow rate/extraction time, is there a difference in particle size distribution that translates into taste changes in the cup? I don't believe this has been studied well enough for any definitive conclusions. In my experience (and we're talking anecdotal evidence here, not scientific), I get a more consistent result when there is an adequate bean mass in the hopper. (Of course I could be wrong. )