Espresso hand grinder review - Kingrinder K2, K3, K4, K5 and K6.
Answering the $64 question.
This review took a great deal longer to put together than I thought. I went through almost a kilogram of coffee beans before I felt comfortable with my findings but here it is finally.
Some time ago I did a comparison between the Kingrinder P1, P2 and K2 hand grinders. You can see that here
My thoughts at the time were that they all made great espresso for use in my Cafelat Espresso Robot, however the differences between them were mostly workflow related. For instance the P series grinders are smaller with smaller grips and straight handles with smaller burrs so they require more effort to grind with and the P2 was more difficult to grind than the P1 due to it's different burr design. The K2 was a much nicer grinder to hold with larger, easier to turn burrs, an offset handle that put less strain on the wrist and a wide rubber grip. The espresso it produced was marginally better than the others but really the big difference was how much nicer it was to use.
Knowing that the K2 was easily worth the $35 price increase I pondered whether the same would be true of the top-end Kingrinder K6. Kingrinder makes six K series grinders but in this comparison I'll focus on the 5 large burred K series grinders numbered K2 - K6. These five grinders are a mix of 2 burr designs in 2 metal coating types using 2 form factors. To do a comparison I didn't need to buy all 5 because of the similarities between them. I've created a table that explains the difference.
K2, K3, K4 have the same 6 point burr geometry and make the same coffee
K5 and K6 have the same 7 pointed burr geometry and make the same coffee
K2, K3, K5 have internal burr adjustments
K4 and K6 have external burr adjustments
If you look at this list you'll notice that the K2 (internally adjustments, 6 pointed burrs) and K6 (external adjustment, 7 pointed burrs) cover all of burr designs and form figures so I was able to do a reasonable comparison with only two grinders.
Burr Geometry
The K2, K3 and K4 have the same burr geometry so in theory they produce the same style of coffee but it should be noted that the K3 and K4 have titanium coated burrs which may make them last longer than the regular stainless steel coated burrs of the other two. Since my test is short the titanium coating would not in theory have any impact on my results. The six pointed burr geometry is very similar to the Kingrinder P1 but superior in that the burrs are 10 mm larger requiring less effort to grind.
The K5 and K6 have a 7 pointed burr similar in design to the P2 but also 10 mm larger lessening grinding effort.
Form Factor
The K-series grinders come in two form factors depending on how grind adjustments are done. The K2, K3 and K5 have internal grind adjustments that can be accessed inside the catch cup whereas the K4 and K6 have a top mounted grind adjustment ring that can be accessed without taking the catch cup off.
On paper the K4 and K6 have 60 clicks per round as opposed to the 40 of the K2, K3 and K5. On paper this could lead one to believe that the K4 and K6 have 50% more granularity in their grind size over the K2 but if you look at the microns per click you'll see that each of the K6's clicks equates to 16 microns and the K2's clicks equate to 18 microns. That's a difference of 10% and so small that it's probably just a product of the 7 star burrs as opposed an intended design improvement by Kingrinder. Going from the P2's 33 microns per click to the K2's 18 microns was noticeable but going from 18 to 16 makes little measurable difference. Because the K6 has more clicks per round it requires a lot more time cranking away on the adjustment dial trying to get into the general ballpark than the K2.
The K4 and K6 have larger 35 gram catch cups which makes little difference for me because I only grind for espresso and the 25 gram catch cup on the K2, K3 and K5 grinders is perfectly fine. However, if I grind 18 grams of beans using the K6 the night before and then grind another 18 grams of beans the next morning while half asleep the catch cup IS large enough to hold it all - I know, I've done it. On the K2 I'm made aware of my mistake halfway through when the grinder stops grinding because it's plugged due to the smaller 25 gram catch cup. For pourovers the larger catch cup could be useful.
All K series grinders have the offset handle that allows the turning knob to orbit around grinder body putting less stress on the wrist of the hand holding the grinder which is an improvement over the straight handle of the P-series grinders. It should be noted that the K4 and K6 have a nice teardrop shaped knob whereas the K2, K3 and K5 have a simpler round knob. This makes a bigger difference than you might think. I'll get back to that.
My Espresso Machine
I'm using a Cafelat Espresso Robot manual lever machine which gives me a ton of feedback and even more control over the shot. It has proven to be a perfect machine to flush out the differences in grinders. My target espresso was a 10 second pre-infusion with a 30 second pull at 9 bars. This is what I started with as the beans I'm using provide a balanced shot using this timing. I did however pull many shots shorter and longer as well as slayer shots just to experiment. I dialed both grinders in depending on how they tasted best which ended up with two different types of shots.
For all shots I used 18 grams of coffee, a wire distribution tool, a leveling distributor and pressure sensitive tamper all built for the Robot. Then the shot was pulled with only the shower screen and no paper or additional screens.
My beans are type garnica, caturra and typica harvested in 2024 from Veracruz Mexico, medium roasted, washed process, fermented for 46 hours and dried in the sun. I chose these for the test as they lean a bit fruitier and a tad more acidic with nice clarity so I thought they'd display the differences between the 6 point and 7 point burrs better. I may run this test again later with another different type of bean that leans in on chocolate and body.
The test.
When I first got my K2 I dialed it in using about 36 grams of coffee total. Essentially I ground some coffee in the DF64 with SSP Sweet Cast burrs, and then just ground out a little with the K2 and felt it, then adjusted the grind, ground some more, felt it again and adjusted again. I kept doing this until it felt as close to the output of the DF64 as I could tell. I then ground a full 18 grams and pulled a shot. It needed to be tightened one click and was spot on. My everyday workflow for the K2 is to grind 18 grams and pull a shot. If the shot comes up 5 seconds short I adjust the dial clockwise one notch and put the catch cup on so it's ready for another shot later. If during the next shot it needs adjusted I move it one notch again. This way I'm using relative adjustments, I don't really know how many clicks from zero I'm using. This is partly because it works but also partly because the K2's design dictates it due to the internal burr adjustment.
I fully expected to dial in the K6 the exact same way but for reasons I still can't explain it just didn't work that way. I went through 250 grams of coffee bouncing around trying to get it consistent and then I ran out of coffee and started a new bag so had to dial both grinders in again. The K2 dialed in within a shot or two and the K6 seemed to need a lot more adjustment to get it close. I'd crank it a few notches and sink the shot and do it again. Eventually I got it pulling decent if not acidic shots. Consistent enough at least that I could start playing.
The flavor results
The flavor results largely come down to the differences in the 6 pointed burrs and 7 pointed burrs. I started with the K2 which can be adjusted down to 18 microns of precision and using the beans that I'd chosen I found acceptable espresso occupied about 3 clicks. One less click and the shot came up at about 25-28 seconds and clearly leaned acidic, two clicks tighter and the shot went 10 seconds longer with the acid being replaced by a lingering bitterness on the end of my tongue. Right between these two, the acid and bitter disappeared. This is what makes it easy to dial in, there's a definite "right" grind for it. I settled on a 10 second pre-infusion at 2 bars and 32-35 second shot at 9 bars for the best balance. I think I've mentioned the beans I'm using like to go a bit long.
The K6 shots always lean more toward acidic. If I tighten up the shot to a 10 second pre-infusion at 2 bars and a 40 second shot at 9 bars it's still acidic but lingering bitter gets layered on top. Going extra long with a 10 second pre-infusion and 50 second shot it's really bitter and the acid is still there. This grinder confuses me a bit. The acid never fully goes away no matter how I grind. This makes me think that it's making boulders no matter what grind setting it's on. As it gets finer the fines get over extracted and the boulders are still there which are under-extracted. I have Kruve sifter plates to test but didn't get around to it. I think they'd prove this out but I'll need more time to know for sure.
The Workflow results
The K4/K6 grinders have a few improvements over the K2, K3 and K5 in that they have external adjustments, and nicer teardrop shaped knobs. Both grinders will grind 18 grams in about 40 seconds so there's no difference there.
When I ground the first shot using the K6 I swore the barrel of the grinder was larger than the K2 as it felt larger and harder to hold onto requiring increased effort. After grinding 3 or 4 shots I was positive that the body was larger so I got out my micrometer to prove it and I was wrong - they're exactly the same size. After watching my hands while grinding I realized that with the top mounted 30 mm wide burr adjustment ring required my hand to be further away from the handle putting extra stress on my wrist. Attempting to "choke up on the bat" resulting in my hand bumping the adjustment ring. I don't think this is a deal breaker but just be aware. When grinding with hand grinders you have 2 types of grinding effort - the easy-grinding effort when beans are being shaved appropriately and then the crush-effort when a stubborn bean needs to be broken up.
Subjectively the K6 feels like it requires less easy-grinding effort than the K2 until a bean catches and then more effort than the K2 to get through it. The K2 feels like it requires more easy-effort shaving away at beans but powers through crushing them. Please note that this is not a scientific test in any way. I have now ground over a kilo of coffee going back and forth between them every 10 seconds. Also note that the K2 is now 6 months old and has been used continuously during that time whereas the K6 is brand new. I can't discount bearing wear.
Summary
I went into this thinking there would be an absolute winner like in the P1, P2 and K2 test but I was surprised that there isn't. I believe for espresso the 6 pointed burrs are just better. They're more consistent, easier to dial in and I can get them to make just about any shot I want (at least with the coffee I have). However the same could be said for the K4 as it has the same burrs.
As for usability, I'm torn. The knob on the K4/K6 is superior. It shouldn't matter that much but it does, it's just nicer to use. Concerning the advantages of external adjustment vs internal I'm not quite sold. If having a top ring requires my hand to be further away from the handle requiring more torsional strength than I'm not sure I want it. If they could put the ring on the bottom then maybe I'd be in. As for the usability improvement of having external burr adjustments themselves, I think that it could be useful but in my workflow it doesn't matter at all. I want to think it's more than just for marketing and I hope it is. External adjustment allows for absolute adjustment whereas internal adjustment makes that difficult so you will have to rely on relative adjustment. What I mean is that with an external ring you can SEE how many times you've made a complete revolution plus you can see how many clicks into that revolution you are. This would in theory allow you to go between two drastically different grind settings quickly. Relative adjustment doesn't allow this at least in the practical sense. You could zero out the grinder and count out your clicks each time you changed it but it's not really practical. Using relative adjustment you just change the adjustment tighter or looser depending on the resulting espresso and don't pay any attention to how many clicks you're at (until you bottom out).
I don't know how practical it would be to crank away on the K6 adjustment burr for a couple of revolutions for a pour over and then crank it back down for espresso. I just don't see it working well that way. For my workflow the relative internal adjustment inside the catch cup works perfectly fine. I wouldn't mind having a bottom external adjustment ring though, I wouldn't turn it down.
Other factors to consider
Both grinders allow you to replace the handle with a drill adapter in case your arm gets tired... I'm not going to lie, I've considered getting an electric screwdriver for it. Note that the P-series Kingrinders do not have this ability. The K2, K3 and K5 are a tiny bit smaller in height, but I don't think I'd make a decision based on that.
There's also the difference in price. I'm listing prices in USD direct from Aliexpress because I don't know where in the world people will be reading this.
K2 - $61.49 ($49)
K3 - $81.49
K4 - $106
K5 - NA
K6 - $110 ($97)
I also found other vendors that had the K2 for $49 and the K6 for $97. These were the cheapest prices I could find. I could not find a price on the K5 so perhaps it's no longer produced. I have a hard time imaging the K4 or K6 costing 60% to 90% more than the K2. I think that for my needs a K3 with a knob from a K4/K6 may be the ideal hand grinder as the burrs would be titanium coated and the knob comfortable.
What's next?
As usual this comparison created as many questions as it answered. I want to test the K2 and K6 with the Kruve sifter plates to analyze the distribution. I also want to try both grinders with my other favorite coffee which is a bean from Oaxaca Mexico and leans into roasty and chocolate notes. Maybe my initial assessment of the 7 pointed burrs was incorrect and it will shine with a less acidic bean.
Of course there is also the question of pour-overs. I will not be testing this as I don't make coffee that way but I wonder how the K6 will do in that regard I will leave that for someone else.
Note: the test with the espresso beans from Oaxaca has commenced - stay tuned.
Could it be the K6 burrs were new and just needed a little more breaking in?