Review: Kruve Sifter for Grinder Calibration

To improve your coffee, improve your grind.

Chances are you’ve heard this advice (or some variation of it) before. And for good reason – it can save you a lot of time spent spinning your wheels making mediocre coffee.

But why is grind so important?

At the end of the day it all comes down to extraction. Here’s the gist: Only around 30% of a coffee bean can be dissolved by water (the remaining ~70% is insoluble material) – but more isn’t necessarily better, and in this case we don’t actually want to extract all 30%. Instead, the sweet spot we’re after is 18-22%.

In other words, if you take the total weight of your ground coffee, 18-22% of it should end up in your final brew. Too little (< 18%) will underextract your coffee and cause it to taste bland, sour, or even salty. Too much (> 22%) will overextract and you’ll end up with a bitter brew.

So getting back to the original question, the reason it’s so important is because consistently achieving optimal extraction is nearly impossible without the proper grind. This requires us to pay close attention to a couple key points:

  • A (relatively) consistent grind size. No grinder is capable of breaking every bean into the exact same size, but it’s important to minimize the proportion of grinds that are significantly smaller (fines) or larger (boulders) than our target particle size. Why? Imagine if you tried baking cookies with many different sizes of dough. You’ll probably end up with some cookies that are cooked perfectly, others not cooked enough, and some flat out burnt to a crisp. Brewing coffee is similar, except all those results (good and bad) combine and contribute to the taste of your final product.
  • Proper grind size. The grind size you’ll require is dependent on a number of factors, one of them being your brewing method. French Press, for example, typically uses a coarse grind – while in comparison, espresso takes a very fine grind.

To achieve a consistent grind, you’ll need to invest in a high-quality burr grinder. But getting the proper grind size? That’s not so straightforward.

Since accurately measuring grind size is difficult to do without expensive lab equipment, we’re left with having to guesstimate based on a subjective description (fine, medium, medium fine, etc.) or vague reference (sea salt, sand, etc.).

But a new product (and successful Kickstarter project), the Kruve Sifter, claims to have “perfected the grind” – not only by improving grind consistency by allowing you to remove unwanted fines and boulders, but also providing a way to objectively describe grind size. According to Kruve, it can even allow you to find the setting on your grinder that’s best suited to a particular grind size – a process the company calls grinder calibration.

I’ve been particularly interested in the latter, so this review will focus on using the Kruve for grinder calibration.

Calibrating With the Kruve

The Kruve Sifter consists of 3 trays and a series of different sized sieves (2, 6, 12, and 15-sieve models are currently available). The largest sized sieve gets situated in the top tray, the smaller sieve in the middle, and the bottom tray catches grinds that are smaller than our ideal range.

The whole sifting process works like this:

  1. Select your desired grind range (e.g. 400-900 microns).
  2. Insert the larger-sized sieve (e.g. 900) in the top tray.
  3. Insert the smaller-sized sieve (e.g. 400) in the middle tray.
  4. Nest all 3 trays together.
  5. Grind your coffee and pour it onto the top tray (Kruve recommends using 10g for calibration purposes).
  6.  Place the wood lid on the top tray and shake for 30-60 seconds.

After which you’ll end up with:

  • Grinds that are too large (e.g. > 900 microns) in the top tray.
  • Grinds that are too small (e.g. < 400 microns) in the bottom tray.
  • Grinds in the ideal range (e.g. 400-900 microns) in the middle tray.

Now that the grinds are separated, the next step is to weigh both the fines and boulders. You’ll want to use a scale that’s at least accurate to .1g, and preferably .01g.

The goal here is two-fold. First, you want the majority of grinds to be in the ideal range (middle tray). You also want to aim for an equal amount of fines and boulders (by weight).

Confused yet? Let’s look at a few examples.

Example 1 (too coarse)

Boulders (top tray): 3g
Ideal (middle tray): 6g
Fines (bottom tray): 1g

In this example we ended up with a much larger portion of boulders (3g) compared to fines (1g). We’ll want to try again using a finer grind setting.

Example 2 (too fine)

Boulders (top tray): 0.5g
Ideal (middle tray): 7g
Fines (bottom tray): 2.5g

This time we ground too fine for our ideal range (2.5g fines vs. 0.5g boulders). Let’s try it again, this time grinding coarser.

Example 3 (ideal)

Boulders (top tray): 1.1g
Ideal (middle tray): 7.6g
Fines (bottom tray): 1.3g

Finally! We’re pretty close to a 50/50 distribution of fines and boulders, which is where we want to be. I’d consider this grinder setting calibrated for our selected range.

On a side note, I occasionally noticed some fines sticking to the rubber seal on the upper (larger) sieve. It didn’t appear to be much and I doubt it’d significantly skew calibration readings, but it is worth mentioning.

Overall, the process is pretty painless, but you’ll probably need to sift and weigh a few times until you find the right setting for your grind range.

Findings

I spent several weeks putting the Kruve through its paces, calibrating my Baratza Vario for various brew methods (moka pot, siphon, and drip) using Kruve’s recommended settings. While I found these did a pretty decent job of getting me in the ballpark of the grind I needed, you can count on having to make some adjustments along the way – factors such as bean type/age, temperature, humidity, etc. can all affect the size of grind you’ll need.

Also, even with a calibrated grind there’s no real way of knowing what the actual distribution of particle sizes is within our “ideal” range. So if you’ve calibrated at 400-800 microns, are the majority of those grinds closer to 600 microns? 500? 700? Just something to consider, since it may mean making some further adjustments.

My point here isn’t to knock the Kruve, just to manage expectations. If you fixate too closely on accuracy and numbers, you may be disappointed. But if you use calibration as a tool to get close to your optimal grind and adjust from there, the Kruve can be very helpful.

A useful approach I found was to create “landmarks” at different grind ranges –  for example, calibrating at Coarse (e.g. 600-1000 microns), Medium (e.g. 400-800 microns), and Fine (e.g. 250-500 microns). Using these landmarks as reference points, I was able to estimate a decent starting point for most other grind settings without having to manually calibrate each of them separately. So using my previous example, for a brew method that calls for a “medium coarse” grind I’d start out with a setting about halfway in between my 400-800 and 600-1000 micron points.

In my opinion, the landmark method is a much better alternative to relying on the settings labeled on most grinders (which can vary wildly even between units of the same make and model). Differences in settings can become even more pronounced as grinders age and burrs wear, as I found out when calibrating an old Capresso Infinity. Turns out, calibrating to a medium grind of 400-900 microns required a setting all the way down in the Infinity’s “Extra Fine” range. Quite a difference!

Bottom Line

Estimating and describing grind size has always been subjective, not to mention inaccurate and generally painful. Fortunately, the Kruve Sifter has managed to significantly improve this process.

Have they “perfected” the grind? No – but aside from a high-quality grinder, I’d say it’s the most useful tool currently available for improving the overall quality of your grind.

The Kruve’s ability to get within the range of optimal grind (though many factors can influence the grind size you’ll ultimately need), objectively describe grind size, and achieve similar settings on different grinders are all groundbreaking features in the home market. Combined with excellent build quality, good customer support, and a reasonable price tag (both the 2 and 6 models are under $100), it’s definitely a worthy addition to any coffee enthusiast’s toolbox.

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