Thanks for all your thoughts, testing, and insight on the 75. I've been mulling the purchase of the Atom 75 for a while and based on your, and other's, observations, it certainly seems like a great grinder overall, if single dosing isn't the utmost priority. Out of curiosity, did you elect for the standard burrs or one of the alternative options (titanium, red speed)?

It would be interesting to grind very light, or very dark roast, immediately after cleaning, then switching to the opposite to see what level of migration occurs to the compacted grounds in the chamber and in the grind path.

Grind retention is always a weird topic. It only makes a difference if it makes a difference to you.

I have had a Mazzer Robur for several years now. It retains 6.5 grams based on cleaning it right out after a month or so of use.

In terms of exchange of what is already retained it is about +/- 2 grams which is the average over 5 shots of weighing 18 grams each time. This is unmodified.

I quite believe 4 grams although the insides of the Atom 75 look like little would hide in there it can compress around and below the bottom burr and in the shoot of course. The variable will be too how sticky your grind is, oily grinds will hang up.

I used the Specialita Mignon for a while and was very impressed. It is as close to single dose as you can get. I sold it as I got a good buy on an Atom 60. I just wanted something bigger and based on my experience with the Robur, grind retention is a non-issue if you use your grinder every day. The first shot of the day tastes and pours the same as the last.

I think it is a shame people have got so anal about single dosing. I don't think the Niche Zero is a great grinder either unless you like the flavour from a conical which I find very very bitter due to fines...and I compared my near new Robur with the Specialita. God what a difference.

I would enjoy your 75 and forget about retention otherwise sell it and get a Niche and be happy with that. My advice though is to keep it.

Hey Grant,

I am definitely keeping the Atom! I am quite happy with it and retention seems to have stabilised under my standard routine so far. I am still weighing before and after but that's a minor inconvenience. The fact that I don't need to employ RDT (no clumping) or WDT (I just move the portafilter while grinding and distribution is excellent) yet I get excellent results is what I was looking for.

The Niche might be a great grinder but I don't think it's for me. Too much plastic and lack of an authorised reseller here (in case I ever have a problem with it) turned me away. Same goes for high-end grinders from US (Monolith anyone?).
I could say that this is going to be my only grinder for the foreseeable future. I am not going able to tell a difference in the cup between this and a Ceado E37SD (believe me, I tried shots from both in the shop), single-dosing works almost the way I want it, so what else is there?

Hi Dave, thanks for the comment. I don't think I came across your review when I was researching the grinder, but reading it now as well as your conclusion on the blow-up system, it got me a bit worried. So, after a month of constant use (and only once using a powder similar to Grindz), I decided to open it up. And let me tell you, I wasn't happy with what I saw.

This is what as I saw as soon as I removed the hopper and the rubber gasket-thingy that holds the hopper in place. I don't understand how did coffee grounds managed to get into that small niche on top, but I suspend that the blow-up system is to blame for that.


And this is what one sees in the grind chute. What a mess!


So, let's open her up, shall we? Well, look at this AWFUL mess. Now I know that the blow-up system is to blame. Apparently, the grinder is not properly designed to funnel the air in the output chute and instead it (along with any grounds caught in the air's path) escapes through the side ventilation openings, making a mess. I was kinda worried about this before I opened the grinder, because whenever I use the bellows I get almost no air from the normal exit chute.


Thankfully, not many grounds got to the internal base of the grinder...


Scratch that. Since those ventilation openings are in the back, this is where you you will find most of your wasted grounds. Thankfully I managed to clean (most of) this mess up by shaking the grinder over the sink and then using a blower. But still.


Following is the top and bottom burrs.



With both burrs removed.


The chute.



I'm feeling something between anger and disappointment at this moment. But how about some testing? After I cleaned up everything and reassembled the grinder, I weighed 10 grams of coffee beans (Brazil, medium-dark roast, not really oily at all)...


... and placed them directly in the chute...


Yeap. The old tamper trick, no hopper this time and no Blow-Up System (...)


I let the grinder run for 10 seconds.


The bulk of the grounds were out in 2-3 seconds, but small trickles of coffee grounds kept coming; at 10 seconds the trickles were very very few so I got into the diminishing results area and decided that would be my methodology. How much did I get out?


Yeah. A retention of 3.4 grams. That is without shaking, blowing air into it or anything else; just two button presses. Let's give it one more go and grind 10 more grams.


Hm. Now I got 0,5grams out of that initial trapped 3,4 grams. I still have 2,9 grams lost in the grinder. Let's give it another go!


That's a bit better. I gave it one more go and I got 9.9 (but I forgot to take a photo of it). I suspect that this is how it's going to be. In total I have so far 3.4 - 0.5 + 0.3 + 0.1 ~= about 3.3 grams trapped in the grinder. It's a pity I don't have other coffees to test how much those grounds are recycled or whether they are simply compacted and never getting out (like Trung suggested), but I will stop here.

I will keep using the grinder. The Blow-Up system can blow-up itself, it is definitely not recommended since it's indeed ineffective and creates a mess. Keep in mind that I had it taped on the sides to avoid air escaping and it still didn't seem to do anything. If you get the grinder, save your money and don't get that!

I'll open up the grinder again by end of February (probably) and see how messy it got without the B.U.S. and will update accordingly. Thanks for reading!

Grind retention is difficult to characterize. The Sette 270 is listed as having less than 1g retention, but I get 3g of grounds every time I clean it (every 2 weeks or so). I think most times, the initial grounds get into all the crevices and new grounds don't get retained.. but no doubt some coffee is exchanged. So finding a big amount of grinds inside "zero-retention" grinders is not a surprise, even if you don't use the blow-up system. Although the bellows may exacerbate the issue of grinds getting where they shouldn't.

I think many manufacturers try to 'modify' (add on) something to their existing hopper style grinders to satisfy the single-dose needs, which often have huge downsides. (I categorize the Flow control option for E61 HX machines, restriction in an HX TS loop, and 'blow up systems' in this class of design modifications). And I don't trust many of the traditional manufacturers to do proper functional use testing on their 'mods' and to report the results accurately.

I'd more trust those designs that are designed from the ground up to single dose and have minimal retention, such as the Kafatek grinders and the Niche (and the Sette 270, but I don't categorize that design as "long-term"). I also don't think many grinders are aligned well (from what I read). Now I'm sure there are other great grinder designs out there, but I'm just not familiar with them.

Since the blow-up system is offered as an option when purchasing the Specialita 75, I would contact Eureka to let them know about this issue. The least they could do is replace it with a standard small hopper.

Clive coffee claimed around 2.2-2.3g of retained grinds for the Specialita 75. Some beans are more static than others, though.
They're tests also show 2.5g for the Atom 65 and 2g for the original 60mm Atom.

If a regular hopper prevents grind getting in every little opening and creases, 2-3g of grind retention is actually pretty good for a commercial grinder with 75mm flat burrs. Gives you the ability to single dose for your every day usage and switch to a full hopper when hosting.

The real question is, what to do now with the blow-up hopper... Blowing balloons for kids birthday parties?

Cheers!

If you take a look at this thread (Eureka - Blow Up System) there are some good pointers on the blow up system.

From your pictures I would guess that that issue was the gasket wasn't seated correctly. This is the part that the hopper sits in and then should make a decent seal with the upper burr carrier. The other thing to consider is the clump breaker and the chute. If the chute is already blocked (normal use) prior to using the a bellow then it requires a lot of force to clear the chute of that clumped up coffee. So if the gasket to upper burr carrier seal is already poor and the chute is blocked then the path of least resistance would be between the gasket and the upper burr carrier and into the body cavity of the grinder.

One last thing to think about would be grind consistency while bellowing. The Atom adjusts via the bottom burr carrier and the top burr carrier is fixed to the inside of the body with some dampers. Normally, when you pump the bellow I assume the idea is the force would bottom out on the top lid of the grinder and the outside of the body. But, if there are spec issues or you are pushing hard enough that you're forcing the hopper down into the gasket and then actually pushing on the top of the upper burr carrier it may be possible to affect the grind size...

InspectorGadget wrote:Grind retention is always a weird topic. It only makes a difference if it makes a difference to you.

I have had a Mazzer Robur for several years now. It retains 6.5 grams based on cleaning it right out after a month or so of use.

In terms of exchange of what is already retained it is about +/- 2 grams which is the average over 5 shots of weighing 18 grams each time. This is unmodified.

I quite believe 4 grams although the insides of the Atom 75 look like little would hide in there it can compress around and below the bottom burr and in the shoot of course. The variable will be too how sticky your grind is, oily grinds will hang up.

I used the Specialita Mignon for a while and was very impressed. It is as close to single dose as you can get. I sold it as I got a good buy on an Atom 60. I just wanted something bigger and based on my experience with the Robur, grind retention is a non-issue if you use your grinder every day. The first shot of the day tastes and pours the same as the last.

I think it is a shame people have got so anal about single dosing. I don't think the Niche Zero is a great grinder either unless you like the flavour from a conical which I find very very bitter due to fines...and I compared my near new Robur with the Specialita. God what a difference.

I would enjoy your 75 and forget about retention otherwise sell it and get a Niche and be happy with that. My advice though is to keep it.

is it possible to ignore retention completely because say you make a pourover with 15g a few times a day
Then almost 1/3 of the grind will be old ones? Wouldn't that reflect on cup quality?
Obviously not a thing if you pull shots after shots...

I have the standard hopper which I don't need and the blow-up system which I can use as is anyway (simply ignore the bellows). I paid extra for the B.U.S. so... yeah...

Unfortunately, the gasket was seated correctly. I made sure of that exactly because I was worried about the side-vents, but I still managed to make a mess of the internals. The output chute was clean as well, and if it were blocked by coffee... well, I would expect this to sort it out (it wasn't anyway, since I found out that the air comes from the vent after I cleaned up the grinder).

I am single dosing with the tamper on top now; no hopper. Retention is as before, predictable, but there's definitely grounds left and compacted inside the grinder. If these act as a barrier and don't make my coffee stale then I can live with it, but you are right, I will contact Eureka just to get their PoV as well. Thanks!