Order of factors for classic Italian 4M’s of espresso is often disputed. I see it as: Coffee, Grinder, Machine and Barista in that order. You need high quality coffee, the basic ingredient of espresso, without it everything is lost. Then you need excellent grinder to get most out of that coffee. Finally you need good espresso machine to get best out of your ground coffee and finally you need barista to put it all together.
Each of these factors is critical, but as you can see, I think that grinder is just a bit more important than the espresso machine, in fact having excellent grinder is a sanity saver.
I spent last 4 weeks using Mahlkonig ProM Espresso grinder and it is the easiest to live with grinder for espresso that I have ever used. Easiest how? Easy to use, quality of ground coffee and of course what ends up in a cup. And keep in mind that I love to single dose (grind only pre-measured amounts of coffee in grinder). I single dose because I change coffees often and there are at least 3-4 coffees in play every day.
I single dosed Baratza Vario, Mazzer Major, Compak K-10 and of course Versalab M3, but for ProM I stuck to filling the hopper with about 5-10 shots worth of coffee and using timed grinding. Reason I did this is simply because grinder is designed to be used like that and I wanted to experience how that plays out given that I love single dosing. I also put the ProM on morning duty. In my house, nothing really tests grinder more than morning duty. Being barely awake I am not on top of my game before couple of cups of coffee and patience is in short supply. So if grinder can make everyone happy in my household during morning ritual it is indeed high praise.
Little bit on ProM Espresso model, which should not be confused with ProM All-Around grinder. ProM Espresso is designed for espresso only and it uses the touch panel on front of the grinder to adjust the timed dosing and setup the grinder. ProM All-Around grinder can grind from espresso to drip grind range and does not have touch panel with display. That’s the easy way to distinguish these two models when you see them. All-Around grinder is not model I used this time.
In heart of ProM Espresso grinder are 65mm steel burrs with belt-drive motor. ProM Espresso and All-Around model do share exact same burrs. Mahlkonig K-30, the commercial grinder also uses the 65mm burrs, but they are different from burrs in ProM. Mahlkonig cuts their own burrs so these are burrs not found in other grinders.
ProM Espresso uses timed operation, whereby you set the amount of time in 0.1 second increments for grinder to be turned on i.e. grind coffee which becomes proxy for weighing the coffee you put in basket. For this to work grinder should deliver always about the same amount of coffee in your basket for given grind fineness and time.
Why is this important? Dose, amount of coffee you use in basket is critical. It determines your flow rate, timing and ultimately how your espresso tastes. In short it controls how much you extract out of your coffee. Inconsistent dose results in inconsistent espresso so using exact same dose every time you make espresso is critical. I don’t mean that amount of coffee you use is always the same for every coffee and even every day, but ability repeat your best espresso extractions is ruled by dose. Once you dial-in your coffee to get repeated results you have to have exact control over the amount of coffee you are using. So how good, meaning how precise timed dosing in ProM Espresso is? I did test where I dropped 170 grams of coffee into the hopper and then set timer so grinder grinds for 6 seconds. Here are the results from first to last dose:
Coffee in: 170g:
Total out: 169g
Notice that first dose is low since burr chamber was not filled completely so the dose run short of target. Then the output is fairly consistent and something you can rely on until the point where it hits 15 grams out. That is the point where hopper was getting empty and there is no bean column on top to consistently push beans inside so the feed rate changes and thus the output.
Retention with beans already in grinder between doses is I estimate about 4-7 grams. This means that after longer pause (first thing it the morning for example) to purge stale coffee you should grind about 4-7 grams and throw them out. Perhaps setting single dose to 3 second purge is good idea.
Timed dosing is very precise as long as there are at least some beans in hopper that ensure constant feed into the burrs. And this is consistent with the grinder design, it is designed to be used with hopper on and timed dosing and it really excels at that.
Note that type of coffee, time for grinding, grind fineness and coffee output are all connected. Finer you grind coffee the longer it takes to grind same amount. For example, if at certain grind fineness you grind for 7 seconds and get output of 18 grams then if you adjust grinder to grind finer, 7 seconds will no longer give you 18 grams output. It will give less since it takes longer to grind finer. And if you grind coarser 7 seconds will give you more than 18 grams in the example.
You can indeed single dose the ProM Espresso, but that in my mind defeats its designed purpose and overall usability. I tried single dosing it and you have to grind finer and grinding does take longer since you need to turn on/off, pulse grinder to get everything out. It also seemed to me that consistency of ground coffee was compromised when grinder was used this way. Trust me as hard-core single doser and just use it with beans in the hopper.
So what about taste? I would say that forgiveness of ProM Espresso is due to amount of fines it produces. I feel its noticeably more than either Compak K-10 and Veralab M3. This makes grinder incredibly forgiving. Its really my favorite grinder for the first espresso in the morning while I am half a wake. I really did not make a single bad espresso first thing in the morning with it. No fuss, no WDT, no nuttating tamp, no Stockfleths move, nothing at all. Just grind, tap portafilter down to settle coffee a bit and tamp straight down. That’s it. Always even extraction as result.
I wanted to show you this forgiveness factor so I made following video. Note that even and nice bottomless portafilter extraction does not guarantee good shot, but it is an indicator. Good looking extractions tend to taste good, bad looking extractions tend to taste bad. It is really that simple. I also wanted to come up with simple way to asses how forgiving and easy to use any random grinder is so this is what I came up with. You grind coffee into the basket, you are allowed to tap portafilter straight down to settle the coffee but no other distributions of coffee in basket or manipulation should be done. You then tamp coffee down and pull the shot. Assess what you get out. This basically eliminates any basket preparation technique since there is no technique. So here is video of ProM in action:
This incredible forgiveness comes at price. There is some grittiness to taste and I feel that these fines are making it into the cup. This taste profile is very similar to Mazzer Major with just a bit more grittiness. There is maybe some clarity of flavor lost due to this as well. The espresso is also a bit more chocolatey (how is that bad :-) ?). Flip side of this taste profile is that it goes very well in milk drinks and this grittiness even enhances them. So its matter of taste really and subjective. If all you drink are milk drinks there are no reservations.
One coffee I was very impressed with when made with ProM was Epic Espresso from 49th Parallel. I used 19 grams of coffee to make 30 grams of espresso and taste was really clean. Acidity and sweetness nicely balanced with tip towards acidity. Bitterness was of high quality, meaning not nasty. The grittiness I experienced due to fines with some coffees absolutely undetectable. Just beautiful cup.
What are drawbacks? The only thing I would improve is the grind adjustment mechanism. I feel like it takes some time for it to settle down so you start thinking nothing changed when you turn the knob. You must, just must, always keep grinder running while you adjust grind. For most grinders if you are adjusting grind to coarser side you don’t have to run the grinder, but ProM requires it. Otherwise it will take even more time for it to settle on new setting.
Also of note is bit of clumping due to the static guard which packs down the coffee so when it exits it appears clumpy. However, I found that this does not create any extraction problems and the clumps are superficial and can be ignored. You just tamp them down.
All in all, I am very impressed by this grinder. If you despaired about your espresso grinder trying to get even nice extraction, if you used WDT, nuttating tamp, stockfleths or whatever voodoo that was required, here is a grinder that does not require all that.
Have questions? Feel free to fire away.