Mazzer vs Rocky
Build - the Mazzer wins, no contest (1-0). It is solid. I have found no weak, cheap feeling or flimsy parts at all whereas the spout on the Rocky spout is a tad fragile. The finish on the Rocky is less than perfect, a bit rough around the edges one could say. The Mazzer is beautifully finished.
Looks - the Rocky has a utilitarian, more modern and an edgier look. It is appealing in its own right, but I think the Mazzer has it beaten (2-0). The Mini is more curvaceous, with "classic" looks highlighted by the stainless bits, especially the doser. To be honest here, I think the Mazzer's proportions are off with the standard hopper. You need the shorter hopper to make it look its best.
Size - the Mazzer is too tall with its standard hopper, but the shorter hopper fixes this. Still, the Rocky is more compact and shorter. This round goes to the Rocky (2-1) with one reservation - just make sure you are happy with how the grinder looks next to your machine. The Rocky looks a bit lightweight next to my Andreja and the Mazzer is aesthetically a better match in my opinion (then again the Rocky would be a better visual match e.g. to a Rancilio Silvia).
Noise - the Mazzer wins (3-1). It is quite significantly quieter when grinding. Both are silent when running empty, but even here the Mazzer has an edge (not that it matters - you don't probably run your grinder much when it's empty?). The tone of the noise is also somehow more pleasing, smoother with the Mazzer.
Countertop cleanliness - the Rocky has several weaknesses, many of which I have commented on in my earlier posts and one of which is the static problem (ground coffee spraying to the counter and clumping). You do need to clean up your counter after the Mazzer as well if you are rushing it and pull the doser lever too quickly/enthusiastically (the ground coffee is thrown to the left and some ends up on your counter). However, if you are gentler and take it a bit slower you can avoid all mess on the counter, though. The Mazzer's catch tray works and is of decent size, the Rocky's is useless. So it is mainly up to you - do prefer you mess contained in a doser that you need to clean or do you want to have it on your counter? I prefer cleaning just one place as the coffee from your counter tends to find its way to the weirdest places. Another round for Mazzer, then (4-1).
Grinder cleanliness - the Mazzer's doser does not sweep all the coffee and I have not yet modified mine for a more efficient sweep. I have removed the finger guard and this makes cleaning a lot easier, including the chute. The chute is exactly what is the biggest problem with the Rocky. It is inaccessible for cleaning unless you remove the spout (attached by two screws). Very inconvenient.
In addition to the daily cleaning I rather frequently do a more comprehensive cleaning, including brushing and vacuuming the grinder throat, the burrs, the chute, the spout/doser - basically all the areas that are in contact with coffee before or after grinding. When you remove the finger guard in the Rocky, you have access to the grinder throat just by lifting the hopper lid. This is convenient. In the Mazzer one has to take the hopper off to gain access (or you can choose to leave the hopper off completely, in which case the Mazzer's throat is as easy to clean as the Rocky's. Removing upper burr carrier for more comprehensive burr cleaning is slightly easier on the Rocky, but not much separates the two here. If it wasn't for the spout preventing the chute cleaning on the Rocky, it would win this round. However, as it stands, I call this a draw (4-1).
Adjusting the grind - we have a hung jury on this one as well (4-1). The Rocky is more convenient when it comes to switching from e.g. an espresso grind to a moka pot grind setting and back. One can do it accurately in a couple of seconds with the clearly marked stepped adjustment and this is easily repeatable, time after time. The Mazzer is less perfect in this sense, especially since adjustment collar is quite stiff when the Mini is new. However, I rarely drink anything else than espresso or drinks based on it and here the Mazzer is superior. I had experienced situations with the Rocky where one setting was slightly coarser than I would have liked and the next setting was a tad too fine. With the Mazzer you can make such minute adjustments that you will have no problem finding the exact setting you want. This may sound like nitpicking to some and with either grinder it is likely that the limiting factor to the shot quality is not the grinder, but the barista.
Grinding per shot - when you discount the mess it makes, and the difficulty in proper cleaning in the Rocky's case, a doserless design is better for grinding per shot. So how do you grind per shot with a dosered grinder? I have found that one can get a relatively accurate amount of coffee ground for two doubles by opening the hopper gate and letting the beans fill the grinder throat and then just turning the timer to around 40 seconds. After a couple of seconds of grinding I close the gate in the bean hopper (this lets just a few more beans in to make sure that there will be enough coffee for the second double). This is surprisingly accurate and I do not waste any more coffee with the Mazzer than I do with the Rocky (with which the waste is caused by the annoying static problems). I do have to do the clicking of the doser lever and use a brush to get the coffee from the chute. This a minor inconvenience. But this round does go to the Rocky (4-2)
Daily use - one can obviously live with either grinder and enjoy great coffee, but there are some annoyances with both grinders. With the Rocky, you will need to stand next to it throughout the grinding process, holding the portafilter with one hand and pressing the grind activation button with the other. This is a bit frustrating as there are other things that you could do during the grind (e.g. milk frothing, cooling flushes for the machine and drying out the filter basket). Also, the Rocky has a problem with beans getting stuck in the hopper - you have to stir them to resume grind. Removing the finger guard helps but does not eliminate the problem entirely.
These problems do not apply to the Mazzer. However, it has its own annoyances. Firstly the finger guard in the doser must be the most useless piece of metal I know - it prevents chute cleaning but serves no apparent purpose (I removed it). Secondly, I do not mind the doser, but the fact that the center portion of the doser retains ground coffee is a bit annoying. To date, in my opinion the annoyances on the Mazzer are smaller than those on the Rocky and hence it wins this one as well (5-2).
Taste in the cup - this is what it all should come down to, right? I was not expecting any major differences in the grind or shot quality. That was not the reason for my upgrade. After all, both have flat burrs not too dissimilar size (58mm in the Mini vs. the Rocky's 50mm) or quality. There are no huge differences in the grinding speed either. The Mazzer turns at 1400 rpm (European version) vs the Rocky's 1700 rpm. The slightly bigger burrs on the Mini more than compensate for the slower rpm (which is a benefit in itself under heavy use) and it does grind slightly faster.
The Rocky I naturally had dialed in and I have my routines honed, so that gave it a slight advantage. As I am new to it, I have not yet had the opportunity to work all the details and routines out with the Mazzer. Having said this, the Mazzer was very easy to dial in. A couple of shots and I was in the ballpark and before the comparison to the Rocky I did experiment with some fine tuning to find the sweet spot.
I cleaned up both grinders of any stale coffee and went ahead with pulling some shots. I naturally held the dose, tamp and distribution as consistent as my skills allowed. As for the coffee, I used the same blend from the same roasting batch for both grinders. In other words I did by best to eliminate all other variables, leaving just the grinders to be the difference. Ambitious? Yes. Realistic? Not really. But one has to try...
Well, my palate is not the most sophisticated and it was further dulled by the summer flu that I have. Drawing definitive conclusions was therefore difficult. Suffice to say that as expected, I did not experience any major differences is the taste of the shots. Trying to be as objective as one can be, and not letting the newness of the Mazzer affect my judgment, I did think there was a very slight difference in favor of the Mazzer. Barely perceivable - I did go back and forth between the grinders to verify this - but the Mazzer seemed to bring ever so slightly more complexity and sweetness into the shots. The shots I pulled using the Rocky seemed to be very slight bitter. I emphasize that the differences were miniscule and small enough to be almost insignificant. Almost. Still, since the Mazzer is already ahead, I'll call this tie.
There was no visible difference in the evenness of the grind and my fingers did not feel the difference either. Perhaps the small taste difference is a telltale of a more even grind of the Mazzer. I have no concrete way of verifying this, though.
Conclusions - A resounding victory for the Mazzer in my opinion (5-2). Others may disagree and are naturally free to do so. In terms of pricing, the difference is surprisingly small, only approximately $100 / €80 at the time of writing this. In fact the difference is so small that I wonder why I did not go for the Mazzer in the first place. Also, the price difference being so small, I do not understand how anyone could justify purchasing a dosered Rocky over the Mini. If you insist on a doserless grinder, fine, the Rocky is good value. However, my experience is that you'd still be happier with the dosered Mini.
It is early days yet with the Mazzer. So do I have any regrets? No. I am already very happy with it and while I am still to perfect my techniques in using the Mini, I also plan to modify it further to fix its most obvious shortcomings...