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The one time I tested grinders I had access to a range of medical grade stainless sieves in a mechanical shaker. they were really quick - probably under 15 seconds per double (15 to 18g) shot. Due to the speed, oxidation was minimised. They didn't clog up at all (probably due high grade stainless lack of static plus the mechanical action itself).
There were three main takeaways -
The best grinders (IMHO, based on flavour in the cup) had an even particle spread to the point that sieving did not leave much "unwanted excess".
Sieving conical grinders output effectively removed the "twin peak effect" of particle spread shared by all conicals. That second peak was blindingly obvious.
The sieving process brought all grinders up to a similar level both in terms of taste and extraction ratio.
My conclusion - sieving is a waste of time if you have a grinder with an even particle spread (think Ditting, Mahlkonig et. al.). The worse your grinder, the more sieving works in your favour.
interested to know how well it works for filter though. the promo videos seem to be quite exclusively demonstrating filter brews (probably because of what you're mentioning here).
which was the largest hole size you started seeing these problems? or are they across the board on most of the sieves?
Just received my Kruve. Packaging and overall look of the product is extremely impressive. Will probably try espresso once, but after that will be mainly for pour over and immersion type brews.
May well fix the moisture problem (if there is one) certainly won't do anything to remove the oils, which I see as the main culprit for clogging.
If cold water wont pass through a 400 micron screen what hope has freshly ground coffee of passing through a 500 mesh screen, very little I suspect.
still, i want to give into wishful thinking and see if it actually does work. otherwise im sure the guys wouldve realized they simply dont have a product on their hands if their largest sized fine mesh (bottom mesh) isnt up to it?
Just received my Kruve. Packaging and overall look of the product is extremely impressive. Will probably try espresso once, but after that will be mainly for pour over and immersion type brews.
Using Kruve Coffee Filters to Make Espresso Coffee. Do They Work?
I ordered a set of six Kruve Coffee sieves some months ago and last Thursday they finally arrived. For those unfamiliar with the Kruve it is a new product consisting of a removable set of sieves of different fineness that fit into a container. Generally two filters will be fitted to the housing at one time, a coarse filter to sift out the large particles (“boulders”) that naturally occur in ground coffee and a much finer filter designed to filter out the small particles (“fines”). Ground coffee is placed on top of the coarse filter and the container is shaken by hand. The boulders are then captured by the top filter while the fines pass through both filters to the container at the bottom. The middle layer sitting on top of the fine filter now contains coffee that has fewer boulders and fines and this is what you use to make your espresso.
The theory is that the boulders extract more slowly when making coffee as they have a larger surface area in relation to volume. The boulders will thus contribute an unwanted underextracted sour taste to the resultant coffee. The fines on the other hand will extract more quickly as they have a large surface area in relation to volume. They will thus contribute a bitter overextracted taste to the coffee. By removing the boulders and fines from the ground coffee the promise is a coffee that is both less sour and less bitter.
Rather than filtering out the boulders and fines the alternative is to use a grinder that producers fewer of them to start with, by producing a much narrower, tighter particle size distribution in the ground coffee. Alas, no grinder can do this perfectly though some expensive grinders such as the Mahlkonig EK43 have much tighter grind particle size distributions than most grinders.
Not everyone can afford an EK43 or has space to accommodate its huge bulk, so filtering out the boulders and fines produced from an ordinary grinder with something like the Kruve seems like a good cheap alternative. We are talking around $100 here rather than $4000.
Well that’s the promise but what is the reality?
After many hours of experimentation, I’ve come up with some tentative answers to this question as well making some observations that may prove useful to other espresso coffee lovers who are also experimenting with the Kruve filters. This is the purpose of this post.
I should say right from the start that I have no affiliation with Kruve at all and I bought the product unsolicited with my own money. In fact, I have no affiliation with the coffee industry at all and am simply a home enthusiast.
Initial impressions of the product
Many crowd funded projects have failed so I was both surprised and delighted when the product actually arrived at my doorstep.
Opening the parcel provided another surprise; the packaging was of the highest order, in fact approaching Apple standards.
Not only was the packaging of high standard so was the product itself. The filter body holder is in beautifully finished anodised aluminium, the lid is solid wood and the individual sieves are constructed of stainless steel. The fit of all components, including the six sieves of different fineness, was excellent and the overall design and aesthetics both clever and pleasing. They even provide an attractive wooden holder for holding unused filters. It is years since I’ve bought a product that greatly exceeded my expectations but that is just what the Kruve sieve set did.
Using the Kruve for Espresso
The Kruve has only been in the hands of users for a very short time so I was not surprised that a web search yielded little guidance from forums about using Kruve. This is particularly true in relation to using the Kruve to make espresso coffee so I quickly realised I was going to have to do a lot of experimentation myself. Right from the start I knew I was heading into the unknown.
The Kruve instruction book gives some rough guidelines. For espresso, they suggest using a 250 um sieve for fines and a 500 um sieve for boulders. Unfortunately, these sieves are only available in the 12 sieve model, the six sieve model I bought being limited to 200, 300, 400, 600, 800, 1000. So that was the first problem; what mesh filters should I use?
As a guide the Kruve website suggest that you should aim for roughly equal quanities of boulders and fines based on weight. While noting the suggestion, the idea of “balance” struck me as somewhat arbitrary as 5 grams of fines may be far more potent in affecting taste than 5g of boulders when you take into account the much larger surface area presented by the fines. Besides grinder particle size distributions are not symmetric so once again the idea of balancing the boulders and fines seemed unlikely. Experimentation was clearly needed.
There were too many variables here for an amateur like me so I decided to hold a few of the then constant. The variables I decided to hold were the coffee blend and the espresso recipe.
The coffee I chose to use was a Kenyan from MyCuppa Roasters. It is a medium roast bean with classic Kenyan lime and cocoa. It’s a good quality commercial coffee from a specialist roaster that has deservedly picked up a few prizes at shows. Overall though it falls well short of the exotic and highly expensive Colombian and Central American Geishas I’ve been drinking lately but there was no way I’d be using these prized coffees for experimentation.
The espresso recipe was 20g in for 40 g out at 94 degrees. The grind was tuned to maximize sweetness and fruity acidity resulting in a 37 second extraction time including 6 seconds pre-infusion at 3 bar. The grinder was a Compak K10 PB, which is a large, good quality commercial conical grinder. It’s no EK43 but it is no slouch either with excellent grind-to grind consistency.
The fact that I was holding the recipe constant is an important caveat as ideally you would like to retune the grind to maximise sweetness and fruity acidity for every sieve combination tested. But life is too short for achieving perfection folks so given the overwhelming percentage of the total grind is in the middle, i.e. is neither boulders nor fines, then I figured the original grind optimisation would still apply to the bulk of the coffee.
The Experiments Start
In the absence of having the recommended 250 and 500 um sieves I used the closest I had, the 200 and 600 um sieves.
I started out with the same grind settings used for the standard unsieved coffee. This sieved grinds looked very fine and when I tried to pull an espresso it unsurprisingly choked.
The choking was so convincing that I figured I should immediately move to coarser sieves rather than just coarsen the grind. So for the second shot I used the 300 and 800um sieves.
The result was better though the 49 second pour was still way too long. For the next shot I coarsened the grind by one division on the Compak K10 and left the sieves unchanged. This time I got a 41 second pour. So I adjusted the Compak one division coarser. Bingo! A 38 second pour with the original recipe of 20 in 40 out.
At these settings the split in the sieves was 4.0g in the top coarse sieve, 21.8 in the middle and 2.0 in the fine for an initial quantity of beans of 28 g. That’s a Iot of waste so wondered whether shaking the Kruve longer would improve the usable grind yield. Here are the results showing how the amount of waste (boulders and fines) varied with the length of time the Kruve was shaken:
30” 10.6g
60” 7.4g
90” 5.8g
120” 5.3g
150” 5.1 g.
Kruve recommend shaking for 20 to 60 seconds. My results for a Compak K10 suggest this is too short. I’d suggest 90 to 120 seconds if you want to minimize waste.
Incidentally I tried regrinding the boulders and resieved the result. This halved the amount of boulders which is a useful further reduction in total waste to around 4g for a 28g dose of beans in the grinder. That a loss of around 14% which is good but that’s only achievable if you shake for 120 seconds and regrind the boulders.
But how does sieving out fines and boulders change the taste of the espresso?
As they say “it’s all in the cup.” Regardless of theory, regardless of claims, if the flavour of the coffee is not improved then it’s a waste of time.
I know you are hanging in for the answer but I simply have to make some caveats to the conclusions I have arrived at:
First my results are based on a Compak K10 grinder. Other grinders may yield different results.
Second I used the same espresso recipe for the sieved and unsieved coffee. It is possible the optimum recipe for the sieved differs from the unsieved. This I am yet to test.
Third I used a medium roast coffee. Light or dark roasts may produce different results.
Finally, the sieves I used resulted in twice the weight of boulders compared to fines. Different rations may produce different results
Enough qualifications; let’s cut to the chase.
In a straight espresso (i.e. short black) there was a noticeable difference in taste between the sieved and unsieved coffee. Compared to the unsieved, the sieved had a markedly less aggressive acidity as well as reduced bitterness resulting in a softer tasting, less strident coffee that was a pleasure to drink. Clarity was noticeably improved with a layered, highly characterised fruity acidity. Indeed I could taste floral characters I had never before tasted in this particular Kenyan coffee which made it taste like a more expensive coffee.
Sounds wonderful doesn’t it? Alas there is a downside and that is the sieved coffee was also a tad blander, for want of a different word. Maybe not bland in the sense of colourless or boring but bland in the sense of lacking as much immediate impact. The best way I could describe this would be comparing a merlot wine to say a cabernet sauvignon. I’ve had wonderful easy to drink merlots and some gnarly old cab savs and found great value in each. The wine that works well while sipping on a veranda after lunch with your partner may not be the wine you like with a steak you are having for dinner. In other words, we need to move away from characterising the difference between the sieved and unsieved coffees as “better and worse” to one of noting and appreciating differences.
But what about milk coffee. What differences did I taste here? Well to be honest, far fewer. While I could pick the sieved short black blindfolded it was much harder with a flat white. Not only were the differences less noticeable, there was also a lesser sense of preference. I clearly preferred the sieved short black but with the flat white I was far less sure. In fact, if anything I may have preferred the unsieved. Maybe it was because the harsher acidity of the unsieved cut through the milk better; I really can’t say. What I can say is that with milk coffee, the difference between the sieved and unsieved coffee was seriously reduced compared to black coffee. Reduced perhaps, to the level of inconsequentiality.
So in the end it comes down to individual preferences. If you a third wave coffee drinker and pour-over enthusiast, who values clarity in the cup in their black coffee then it is likely sieving is going to deliver for you big time.
If your preference is for the Italian style of coffee using dark roasted beans to make intense, punchy, sugar-bolstered espresso then I suspect sieving offers you little. It may even take your coffee backwards.
And if milk coffee is your thing then sieving should not be on your short list as it unlikely it will make little difference you can taste in the cup.
And as for me, well I’m definitely going to explore sieving further. I’m fascinated what it will do to the taste of the gorgeous Colombian Esperanza Gesha I bought from CoffeeSnobs BeanBay and have ageing on my shelf right now.
Last edited by ccgnome; 4 February 2017, 09:25 PM.
Maybe I'll grab one to try - probably not something I'd use as a matter of routine, but I wonder if it could be useful to compare the performance of different grinders, and to gauge burr wear over time. Cheaper than a spectrometer!
Many thanks to all.
A very interesting read, and since I love a double with silky milk, I will forget the Kruve.
And made with an EM 480, EM 6910 (which has done over 10,000 shots)
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