Kruve – follow up.

 

Following on from https://markwjburness.wordpress.com/2017/04/29/kruve-what-can-it-tell-us/

My sieves in the larger sizes (1200/1400/1600) arrived. Initially, I tried 500 & 1400, but the 1400 only separated out a few % at the larger end of my usual settings (not enough to make a difference should I choose to remove it). The 500 tended to leave me with a cut-off around 20%+ at the smaller end. Whilst useful if I wanted to discard the smaller particles, dropping this to a slightly smaller sieve would give me better feedback on characteristics when sifting.

Since I rarely remove the smallest particles, I figured I’d go back to 400 as the smallest sieve & also dropped the largest sieve to 1200. This x3 interval in mesh size equates to a standard deviation of 1.73 when 68% of the ground weight falls between them. This seems realistic with respect to the hand grinders I typically use. It also sits very well with my settings for 1 mug, manual drip brews.

Also, 400 as the smallest sieve will help when it comes to sharing grind settings as everyone who has a Kruve has the 400 sieve.

I also thought I’d tweak the way I record results, I figured a straight line graph would be simplest. When comparing two grinders at an equivalent setting, the closer to vertical the plot, the less of the ground weight falls outside of the sieves & the tighter distribution.

The three grinders shown below all hit mid-box extractions, with the same recipe [see, “Hario V60 Recipe for 1 mug, light/medium filter roasts.”] at the settings shown.

The Feldgrind & the Lido E are so close as to be basically the same distribution as far as this method can detect (standard deviation 1.7). The Porlex Tall has a slightly wider distribution (standard deviation extrapolated to be ~1.9), but not so wide as to make it significantly worse. Indeed, if I set the other 2 grinders coarser & stretch out the pour, I can still hit tasty, mid-box extractions at a coarser grind and a standard deviation of over 2.0.

Setting a Lido E, or Feldgrind so that 11-12% passes through the 400 sieve (2 minutes of shaking) should result in essentially the same grind setting as shown below. Typically, no part of the distribution is removed in my daily brews. However, removing just the portion over 1200 & correcting the dose weight back to 13.5g can allow a sweeter & higher extraction, without upsetting other aspects of the recipe.

Kruve vector Porex LidoE Feld

You can save your own template from this Google form: https://docs.google.com/spreadsheets/d/1jXCV7TVuCAn4rPPyCVtSlD8kROhF267ePbe5iLIvE7c/edit?usp=sharing

Enter sieve mesh size, grinder details & weights captured, as required in the yellow shaded cells (all others self populate). Don’t delete all the info (name & weights) for any one grinder as you might then lose a plot & the legend colours won’t tie up any more.

EDIT: Standard deviations quoted only apply to grounds sifted with the Kruve sifter, these are not transferable to wire mesh sieve analysis.

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Chemex with colander as shower screen.

At home I generally prefer to make small drip brews (by the cup/mug), but in the office my work colleagues prefer quick, hot coffee at the start of the day, rather than putting up with long brew times, my perceived obsession with ‘perfection’ & increased faffing for incremental gains in cup quality. Experience suggests that three mug (~600g output) drip brews appear to be the quickest & most consistent way to achieve this, whilst still catering for my fuss-pot tendencies when making ‘a hot brown drink’ 🙂

The off-putting thing, for me personally, is that I tend to find more undissolved solids making their way into the beverage as manual drip brews get bigger. Even at ball-park extractions the brews can be less sweet. I found that simply grinding coarser, after a point, made it hard to achieve good extractions, no matter how much you stretched out the brew. In fact, this could have an undesirable effect in that increased agitation of the bed made matters worse, cups could be under-extracted and silty.

So, following on from using an Aeropress to disperse the water for Kalita Wave 185 brews, I happened accross a collapsable colander that just so happened to fit snugly into my 3-6 cup Chemex when used with Hario 03 filter papers.

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Unlike the Kalita & Aeropress combo, blooming can be done via the colander/screen. Blooming pour is a spiral to cover the whole bed, then a quick shake of the brewer. Remaining filling pours (8 for most coffees, maybe just 6 for a very soluble Kenyan, for example) go straight in the middle of the colander. As with the Kalita & Aeropress, expect to see crystal clear brew water sitting atop the bed at draw down. Resulting brews are noticeably cleaner in the cup.

Brews have been 40g dose to 660g, or 675g brew water. With a 30second bloom, I typically aim around 4:40-5:00 total brew time (to dry bed), when sifting out of the largest 15% by weight (using a manual, conical hand grinder). Perhaps aim more for 4:15-4:35 total brew time for medium/light roasts, without such sifting.

Kruve – what can it tell us?

Kruve Lido 0.5 0.63 0.75

As well as allowing us to ‘top & tail’, or ‘top or tail’ our grind distributions, sieves can also tell us something about our grind distributions.

I decided to dedicate one of my grinders (Lido 1) to optimising via my Kruve, but still allowing for use without sifting, for days when I just didn’t fancy the additional effort. Immediately it was obvious that 400 & 800 size sieves excluded a huge amount of my grind distribution with my Lido 1. Also a grind centred between these sizes was too fine for my regular drip brewing method. Therefore, I fitted the largest size I had (1100) in the top section and a reasonably fine sieve (350) in the lower section. This gave me…

Kruve Lido 0.75 between sieves

At setting 0.50 from marked zero I landed 69% of the ground weight between 350 & 1100 sieves. This suggests my standard deviation for this grinder is less than 1.773, calculated as SQRT(1100/350). As an aside, I found that 400 & 1100 sieves gave me 68% between them and a standard deviation of 1.658 for this grinder, in this range. (SCAA & ECBC drip grind recommendations echo E.E. Lockhart’s 1950’s analysis, aiming for a standard deviation of 1.414, but this does not seem to be absolutely necessary for smaller brews).

Setting 0.63 also landed a healthy 66% between these sizes, with an even balance between sub 350 (16%) & larger than 1100 (18%) particles. Note that there is typically a bias towards the smaller end with most usable grinds, so this shows I am already coarser at 0.63 than will leave me with the average grind setting targeted by these sieves (620 Kruves). This would be an ideal place to stop, however, this was still slightly on the fine side for what I wanted, with my 1-mug V60 brews averaging 21.5%EY without sifting & removing any portion. I would be happier with a 20.5%EY average for a complete grind distribution, though I can exceed this happily when removing the largest 15-20% of ground weight.

Setting 0.75 gave 62% between the 350 & 1100 sieves. This is not a sign that the distribution is getting worse, but simply that I am now so coarse that I won’t fit the distribution within these sizes to +/- one standard deviation. Again, note that the sub 350 particles are now a much lower % than those larger than 1100.

Another way to view these results might be like this, with cumulative & diminishing weights at each interval, for each setting…Kruve Lido 0.75 cumulative & declining fullCool, eh? Kind of ‘X-ey’ 🙂 But probably a little hard to grasp until you blank out the area above 50%…

Kruve lido 0.75 cumulative & declining 50%

This now gives us a more intuitive hump/peak type diagram. The farther left the apex of the trace, the finer the grind. The farther right the apex of the trace, the coarser the grind. The more acute the angle between the cumulative & diminishing traces for the same setting, the tighter the distribution. The more obtuse the angle, the wider the distribution. Look at how the black ‘0.75’ trace almost touches the red 0.63 trace at 350. Blue (0.50) & red (0.63) traces are very similar & virtually parallel between 350 & 1100.

For now, I have settled on setting 0.69 with 500 & 1100 sieves. I get a maximum of ~20% under 500. This allows me to save a little time by being a coarser than I need to remove the bottom 15%, or so, for immersion brews. The 500 is also quicker & easier to clean.

This setting also retains ~20% on top of the 1100, which I discard for drip brews. Kruve have just announced availability of larger sieves, so I intend to replace the 1100 with a 1200, to allow me to sift out either the bottom 15% or the top 15% at will, depending on brew method.

Kruve Lido 0.69 between sieves

 

 

 

Aeropress & Able disc as shower screen for pourover brews.

I have been enjoying my Kalita Wave 185 brews, but not finding them quite as consistent as I might like, also (maybe due to the shallower bed) noticing a little more non-dissolved solids in the cup. Let’s not forget too that I’m actually pretty lazy…finding a method that allowed me to use the same grind setting & pour regime as a single mug V60 brew (see previous posts for V60 recipe) was also a factor. Maybe I should have said that first…?

Years ago I bought a Swissgold KF300 (AKA Frieling ‘Coffee for one’) & whilst useable, it seems to retain water above the shower insert and there’s little space between the insert and the bed. Coffee also tends to find it’s way up the outer walls of the insert. I guess, like many folk, I have  few coffee brewers not actively employed all of the time. So, I thought I’d try using the Aeropress with Able disc in a similar fashion, but suspended above the Kalita brewer. Able disc is the ‘fine’ version if it makes a difference, I have also tried a paper Aeropress filter but found it held the water back & results weren’t good enough to encourage me to persevere, without also changing too many other aspects of the recipe.

Grind & weigh coffee dose, add to Kalita Wave 185 placed on mug/cup. Slide cup/mug & Kalita Wave 185 into the brew stand, sitting under the hole. Also place the Aeropress on the scales/brew stand so that when you later place it over the Kalita Wave, it doesn’t throw out your brew water weight after the bloom:

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Bloom from your gooseneck kettle as normal, directly onto the bed, then stir/shake the brewer to ensure even wetting. I did initially try blooming through the Aeropress too, but extraction dropped, maybe due to insufficient agitation?

IMG_2053

Whilst the bloom is…erm, blooming, place the Aeropress on top of the brew stand, ready for the brew water. At the end of the bloom time pour the brew water so that the stream falls straight down from the kettle spout, ideally landing in the centre of the Able filter.

IMG_2054

After adding the last of the brew water give the Kalita Wave 185 & cup/mug a little shake to ensure grounds are washed off of the filter wall, though I am typically seeing far less grounds on the filter wall with this method. Note: I generally brew one single mug at a time with my Kalita Wave 185, using 225g of brew water. You can’t easily see the slurry level in the brewer using this method, so be sure to visually check slurry level between pulses if making large brews that could potentially overflow the brewer!

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I feel the cups brewed in this manner have maybe less body than the traditional method, but improved clarity of flavour wins out for me. I am also finding this method more repeatable…but that may say more about me than the Kalita Wave in normal circumstances.

Obviously, if you don’t already own all the equipment mentioned, buying it all to emulate some crank on the internet is probably not the most cost effective route to a tasty cup. A good auto drip brewer can be had for about the same money.

Fines don’t over-extract.

I grow more & more confident of this.

Fines* affect flow rate in percolation. They need to slow the flow enough to extract the bulk of the bed. Too many and flow will be slowed to the point that the bulk of the bed over-extracts and you exceed good tasting solubles yield. Go finer still & they plug the bed, forcing water through paths of lesser resistance (channelling if you will), extraction drops because the whole bed cannot be extracted evenly enough, but the minority of the mass is over-extracted giving a low extraction with predominantly bitter flavours.

In immersion they make their presence felt by actually getting into the brew as undissolved content. Too many and the brew will be bitter, but still at a level of extraction that would otherwise be sweet and balanced if fines were mitigated by grinding a little coarser or sifting out the smallest component.

Fines typically facilitate the over-extraction of larger particles, or lead directly to bittering flavours by coating the tongue, but are likely not responsible for an excess of soluble solids in themselves.

(*…if anyone can actually agree on a definition, that is – E. E. Lockhart suggested the <5% at the fringes of normal distribution, all other definitions I have seen seem somewhat arbitrary, with the exception of the 2nd peak in espresso grinds at ~50µm)

 

 

 

Drip brewing: Brew time & extraction.

For a given brew ratio & brew weights, it is fairly normal to bloom/pre-wet for a specific amount of time, add water at regular intervals, or by a given total time, then aim for reasonable window of time (+/-15 seconds might be reasonable for a number of brews across different coffees) for that brew to end (at perhaps a visible dry bed plus drip time).

However, if your brew time deviates, proportionally, less than your extraction yield (e.g. the same brew time results in inconsistent extractions), you lose a mechanism for controlling the brew. To use brew time to it’s best advantage, your deviation in brew time should perhaps be greater than that of the extraction yield (e.g. a reasonable deviation in brew time still results in consistent extractions).

In my least consistent recipes there seems to be a trend in that the standard deviation (Sdev.) of total brew time has been close to, or less than the standard deviation in extraction yield (calculated as a proportion of each parameter, by dividing the Sdev. by the mean brew time and EY).

If your brew time deviates by around 1.3 times, or more, than that of the EY, this actually seems to make it easier to brew consistently.

Long story short, you may not be able to rely on brew time alone to ensure consistency, without cross referencing against EY.

 

 

 

Manual brew method consistency – further thoughts…

The various coffee associations depict ideal extraction boxes of a 4% span of extraction yield, all centred at 20%EY, encompassing 18-22%EY (although this standard actually goes back six decades). For a given brew method, how achievable is this across a range of coffees?

Several tests of 10 brews each, a different coffee for each brew (within my typical preference, e.g. various recent roasts from speciality roasters, not going from the lightest of the light to supermarket, old, dark  roasted coffee sat on the shelf for months), shows that this range of 4% EY should be your absolute minimum target for your default grind setting & recipe. In fact, to achieve 95/100 brews in this range, 10 reference brews would typically need to fall within a 3%EY span & a standard deviation of ≤0.88%EY.

If you cannot keep the vast majority of brews within this range, assess your method, look at how you can reduce margin for error (careful weighing of dose/brew water/finished beverage & timing – repeating each step the same way, as much as possible, for each brew). Establishing whether or not you are achieving this is going to be very difficult without measurement.

With care, a standard deviation of ≤0.80%EY is certainly possible, suggesting the vast majority of brews, across different coffees, landing ±1.81%EY. This is without changing any aspect of the recipe, including grind setting.

Singling out a single coffee reduces variance further, a standard deviation of ≤0.5%EY is certainly achievable with care. For example, using the V60 recipe in the previous post (weighing brew water and killing the finished brew to the gram in the cup), 10 brews gave me a standard deviation of 0.34%EY, with 8/10 of the brews spanning 0.01%TDS (this is smaller variance than the precision specification of my VST Lab II).

I’m aware that there are differing views on the relationship between brew time and consistency of extraction, but these 10 brews all fell within a 15 second total span, with a standard deviation of 4.4 seconds (or, 3% of the flow time post bloom until no liquid standing above the bed). However, I wouldn’t discard, or write off a brew, based on time – always taste & assess, different coffees may take different times to reach the same EY.

Why is this relevant? Well, like many home brewers, I am regularly changing coffees. I want as little waste & as few disappointing cups as possible. I want to make as few & as small adjustments as possible, to maximise the strike rate of good cups. In short, I want to be able to spend less time chasing down variance from coffee to coffee & more time relaxing & enjoying good coffee. A little groundwork up front, evaluating your brew method & recipe, can pay off in the long run.