The science behind Kasuya 4:6 method?

Coffee preparation techniques besides espresso like pourover.

#1: Post by dsc106 »

Anyone tried brewing with this much? ... ing-method

Anyone know the science of why you could adjust sweetness/acidity by varying the amount of the first pour, and strength by varying the number of pours?


#2: Post by ojt »

I pretty much agree with Jonathan Gagne on the "science" of the 4-6 method (and most of other coffee "science" out there):
Another thing that really frustrated me when researching this topic is the amount of pseudoscience one encounters on the subject of specialty coffee. Surprisingly enough, some of the main culprits include previous world champion baristas (hmmmmmm Kasuya, are you using these magical self-transmuting beans again ?)
Now, the method might work for some (you?) with their equipment and beans and water, etc. That's all good and fine, but it is by no means an be-all end-all method. From what I've heard in Japan there is some trend towards darker roasts and Kasuya himself tends to optimise everything so that he can use coarser grinds (see his Hario gear line). Again, if that works for you then that's good.

Sorry, didn't really answer much but wanted to point out the fact that there is no one method to rule them all :)

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#3: Post by cafeIKE »

The one constant in brewing coffee is there isn't

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#4: Post by dsc106 (original poster) »

Ah, I didn't realize Gagne thought it was pseudoscience. I trust his opinions (his book on filter coffee is great... dense, but great!).

I'd like to ask another tangental question, inspired by the "The one constant in brewing coffee is there isn't". I've been feeling a bit overwhelmed in brewing drip lately, or rather in my pursuit of perfection/understanding. And the answer probably lies in just accepting the fun of the art itself. Regardless, one thing that has me a bit vexxed lately is all the varying guidelines on temperature.

I understand the general "hotter for lighter" and "cooler for darker" principle, as more heavily roasted beans need less work to extract and too high of heat can over-extract and lead to bitterness.

Yet I read so many conflicting things with temperature. Some say medium roasts should be RIGHT off boil as close to 212F as possible, others say 205F, others say 195F. Rao (and Hoffman) seem to suggest 212F, pointing out that you lose about 8F from the kettle temp by the time water hits the actual coffee. Then there is the question of keeping the water on the electric kettle between pours to keep it consistent, vs a gradually declining heat.

Yet Blue Bottle says ~200F. Coava coffee (where I have a subscription to) says ~205F. Rao says ~212F. Kasuya in his 4:6 Method claims ~195F (and only around 200F for light). Is the ideal temperature for the brew also related to the ratio (i.e. should a lower ratio brew have a higher temp since you're using less water per gram?). Is it related to grind size (i.e. if you grind finer, go cooler)?

Bottom line - I am a bit overwhelmed/confused as to what the ideal kettle water temperature is for a medium/light roast percolation pour over. How can such a wide range - from 195F to 212F of kettle temps be recommended for medium/medium light roasts?


#5: Post by Ejquin »

I posted something very similar to another question that was asked in another thread, but I just think of things in terms of extraction and try not to overthink too much - hotter water = more extraction. Cooler = less. I start with the idea of trying to extract as much as possible until the coffee no longer tastes good. I also don't want to be varying a bunch of parameters to dial a coffee in. So I just go with highest temp water I can (just off the boil), and then use grind size to adjust what is ultimately extracted.

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#6: Post by cafeIKE »

As an enginerr [retired], IMO the biggest flaw in all recommendations is a lack of rigor in how measurements are taken, the brew device, the ambient temperature, air flow, etc.

A lot work I did involved environmental chambers on products with close tolerance and we called for "pretty tight" specifications. My cousin who worked aerospace just laughed at what we called tight, always saying we were missing a couple of naughts after the decimal point.

Coffee is an organic compound and unless everyone is in the same room with the same coffee from the same roast with the same water, brew hardware, and the same panel evaluating a lot of recommendations don't even rise to the level of interesting reading.
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#7: Post by Jonk »

Ejquin wrote:So I just go with highest temp water I can (just off the boil), and then use grind size to adjust what is ultimately extracted.
While this is a pretty good approach, Gagné writes in his book that there will be differences in what you extract and that you can't reach the exact same target by only adjusting water temperature or only grind size.

It's not so simple that a hot temperature will always work better for light roasts either in my experience. I used to brew with 212F/100C to at least keep one constant and was satisfied with this for the medium to light roasts that I enjoy.. But then I started brewing with 205F/96C just to be on the safe side. It wasn't until I tried going back to 212F/100C that I noticed a certain character imparted that I don't enjoy. I might have upgraded to a better brew grinder before this so that's another factor. Some quite light beans also seem to work better with 195-198F/90-92C so I believe you just have to live with the added complexity to get the most out of your brews.

Both temperature and grind size will impact brew time and that is what I have sacrificed instead. So far so good, it seems to me that it has the least impact of the three as long as it's not too short. All opinions subject to change however :lol:

There are some things about 4:6 that I think Gagné would agree to, for example:

..if the wording was changed to: multiple pours should increase extraction.
Doing a second bloom to ensure it's completed is also kind of trendy.
Kasuya even designed a brewer that leads to less bypass before that was a thing.

So it's not all bad. I don't like how letting the water level drop below the grounds will allow the temperature to plummet and the absurdly coarse grinds, but perhaps it's a matter of what beans and grinders are used.

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#8: Post by dsc106 (original poster) »

So I've been thinking about this method today, and I think there may be something to it - something Gagne may be mistaken on.

We know that coffee extracts in the order of sour (acidic) -> sweet -> bitter.

I've been researching profiles for my flow control device, and it seems that light and fresh roasts benefit from a "low & slow" pre-infusion before going to full pressure. On the contrary, older or darker roasts benefit from starting at full pressure, and then dropping to a lower pressure with a gradual tail off. The long low pressure pre-infusion tones done bright and acidic shots, whereas the hard up front hit lifts the bright notes in a darker roast.

Kasuya's 4:6 method here seems to mirror this sort of profile on how he calls for more or less water in the initial pour to control acidity. It would stand to reason that pouring more water immediately upfront does a couple of things. One, pouring more water creates more agitation which creates more extraction. Two, more water allows it to hold thermal mass better in the brewer, and more temp allows for more extraction. Three, more water volume allows for less resistance to diffusion of soluble, and less diffusion resistance means more extraction (Gagne has a whole section about this in his book, about the physics of diffusion - more on this later).

Now, we could phrase at such: being "gentle" with the coffee right up front extracts less sour/acidic/bright notes. Being "aggressive" with the coffee right up front extracts more sour/acidic/bright notes. Mirroring this same pattern found in espresso flow profiles, Kasuya seems to find that using less water on the bloom phase makes the coffee sweeter in the end. A better way to phrase this might be, using more water (i.e. more agitation, less diffusion resistance, and higher temp) on the initial pour, more acidity is extracted. Using less water, less acidity is extracted. In the final cup, one will note the cup "seems" sweeter since the acidity has been toned down (in reality, the same amount of sweetness should be present either way, it will just be more overpoured by acidity if you use more water on the first pour).

Moving on to the "60%" (6) portion of the method, which determines coffee strength by the number of pours. Actually, this would align with something I was theorizing the other day in this thread:

"High Extraction Brews vs Two Stage Immersion Filtration?"
High Extraction Brews vs Two Stage Immersion Filtration?

Again, Gagne has a chapter on this in his book as referenced earlier. Essentially, soluble dissolve in a body of water. The more soluble are in a given water, the slow diffusion will continue to occur. This is why immersion brews are forgiving - extraction doesn't scale linearly, it slows more and more as the water becomes more saturated. The same thing is happening in a pour over, just at a lesser scale. Each pour and percolation phase is a mini immersion. The fewer pours, the lesser the extraction, because the water is becoming more saturated and diffusion happens slower. Kasuya seems to find that the more you refresh the water, the more solubles are extracted, hence he scales strength with doing more pours. This would seem to follow Gagne's findings, as well as my speculation in the thread above: if you "refresh" the water more, you will pull more out of the coffee.

Well, this is my best attempt to make sense of the science behind the Kasuya 4:6 method. Or maybe it is pseudoscience afterall, but as I think about it, it may well just make too much sense and match what we've observed with extraction elsewhere.


#9: Post by vit »

More pours actually easily explain "stronger" coffee, because time between each pour is still 45s, so with 1 pour more, we also have 45s longer extraction, although with less water per pour and probably lower average slurry temperature (didn't actually measure it). However, this part is a bit unclear - I can't find that he said to shorten the time between pours in that case (or extend the time between them in case there are 2 pours in the 60% phase)

Not sure about first two pours controlling the acidity

I'm a beginner in pourover (being espresso fan for a few years), tried Scott Rao's, James Hoffman's, some combinations of them and finally this method and to my surprise, this one worked the best so far. Since the number of samples so far is low (around 15) I'm not making any claims this is the best method, but it was certainly most beginner friendly to me. One of the reasons might be that it seems to be better suited to lower than usual quantities (around 13g in my case, using V60 1 cup - which is more than enough for me) though I thought it would have been the opposite. There are other "pulse pour" methods as well, like April method (4 pours every 30s) which I didn't try yet

To me, it seems that pulse pour methods on coarser coffee (like this one) work as combination of drip and immersion brew - during the pour it's dominantly drip, between the pours it's dominantly immersion, as not all water is drained into the cup

Using medium roast Ethiopia and Columbia that I previously tried as pourover in my roaster's cafe (which inspired me to try making it at home) btw


#10: Post by ojt »

I think in the end what is important is the temperature, and avoiding channeling. I myself have the Origami and I have found that a bloom + 2 pours is the sweet-spot-method for most coffees I enjoy, and I need to preheat the cone well. Doing more pours I risk loosing too much heat and probably my bad pouring technique will start affecting the brew more. I should probably get a nice probe for measuring stuff, so far it's just my taste buds :)