A paper on Espresso Extraction - Page 2

[another_jim]

Hi Andy,

You know me, so you know I was up all night trying to get a handle. The handle is fairly straightforward.

The variables you control (the causes) are grind, dose, basket, and shot time. The outcomes (the effects) are shot weight and post shot puck weight.

There's no problem when you use an outcome on the Y axis and a cause on the X; or use the same set up in statistical tests and regressions. Once you start mixing this up, or using ratios of inputs and outputs, outliers and other residuals start behaving in linked and funny ways. The apparent relations can change in strength wildly as the models are very slightly changed. This flaw applies to all the analyses so far, even the rank one, since we were using shot weight as a cause, and a lot of ratios of input and output variables.

Unfortunately, using the raw data, rather than ratios, gets lousy models. I need to do more work.

[AndyS]

Hi Andy,

You know me, so you know I was up all night trying to get a handle. The handle is fairly straightforward.

The variables you control (the causes) are grind, dose, basket, and shot time. The outcomes (the effects) are shot weight and post shot puck weight.

Fortunately it sounds like it was a satisfying night for you rather than an annoying night. Of course, let me know if there is any more data I can collect. And good luck!

[another_jim]

Fortunately it sounds like it was a satisfying night for you rather than an annoying night. Of course, let me know if there is any more data I can collect. And good luck!

I've tracked down the problem: we're making good shots.



The graph has shot time on the X, shot weight divided by dose on the Y -- I call the graph the "al effect," since we are drawing out the more concentrated shots, cutting the less concentrated ones short. The result is that the points are mostly in the lower left triangle; and the upper right one is mostly empty. This is for my data; but you'll probably see it on yours too.

This selectivity on on stopping shots messes up the statistics and the physical relations. Long shot times should produce higher solubles yields, higher weight shots, and less concentrated shots. By using al's rule (or the blonding rule), we stretch out concentrated, low flow shots and cut watery, high flow ones short. In my dataset, this has completely removed the causal relation of shot time. I'm guessing you have a similar situation.

Despite messing with the analysis, this could be a good thing. Afterall, we are looking for effects in shots made by competent baristas.

[WR]

I've been watching with interest since your earlier thread about lower dosing. Your hard work has spurred us to experiment and find a better tasting cup for the effort. Just wanted to say thanks for sharing your work. You are one seriously obsessive guy, please stay off the meds and keep on pumping out the data! Will

[Philg]

Thanks very much for your work, I get a little panicked (and lost) with the data but I still enjoyed reading the papers and am excited to have new things to try. I had it in my head that grinding too fine meant over extraction and that too little coffee in the basket was just a bad idea. I haven't made a better shot yet, but some OK ones (after a string of lousy ones with my regular way of doing things) by trying a finer grind / smaller dose. I'm no researcher but it has been exciting and fun, which is mostly what I'm after.

Thanks,
Phil

[another_jim]

So Abe Carmeli got a chance to taste some of the ultra-lite roasted, downdosed espressos. He agreed they were tasting in the high 4s and low 5s. Body was another story, 3ish, even for the ristretto pours. The ultra-lite roasts simply don't have that much body, even if solids in the cup are kept high.

He's more of an acid head than me, preferring dosing around a 1/2 gram higher.

[AndyS]

So Abe Carmeli got a chance to taste some of the ultra-lite roasted, downdosed espressos. He agreed they were tasting in the high 4s and low 5s. Body was another story, 3ish, even for the ristretto pours. The ultra-lite roasts simply don't have that much body, even if solids in the cup are kept high.

That I agree with that observation. With the light-roasted, downdosed shots, the flavors can be balanced but "there's no there there" (apologies to Gertrude Stein).

[peacecup]

I may have missed this in my brief review of the paper, but how does shot volume relate to all this? E.g. I using a small-group lever machine (45-mm Ponte Vecchio), which requires two pulls to get a 1-oz ristretto. I have been used to dosing very full (15g) but am now determined to try down-dowsing, since I like the sweeter flavors. My first test confirmed the possibilities - the shot was sweeter.

In your conclusions you discuss the tendencies for Italians to dose less for practical reasons (btw I think you should move this up to the Intro). I am correct in assuming they are dosing 13 g for full 2-oz. doppios? So how do they get this much volume without blonding? I doubt I could get a 13g, 2-oz shot without serious blonding on my lever machine.

PC

[LeoZ]

I may have missed this in my brief review of the paper, but how does shot volume relate to all this? E.g. I using a small-group lever machine (45-mm Ponte Vecchio), which requires two pulls to get a 1-oz ristretto. I have been used to dosing very full (15g) but am now determined to try down-dowsing, since I like the sweeter flavors. My first test confirmed the possibilities - the shot was sweeter.

im not an authority on this, but from what i read, the entire paper focuses on it..

In your conclusions you discuss the tendencies for Italians to dose less for practical reasons (btw I think you should move this up to the Intro). I am correct in assuming they are dosing 13 g for full 2-oz. doppios? So how do they get this much volume without blonding? I doubt I could get a 13g, 2-oz shot without serious blonding on my lever machine.
PC

this is also covered in the paper, the 2nd link in the abstract:
http://users.ameritech.net/jim_sc..._extraction.htm#_b

and in a previous thread by Jim:
http://www.home-barista.com/forum...ference-t3182.html

[another_jim]

Ok. One of the things I was assuming when I started the research is that the perception of the coffee's body and strength mostly depended on how much coffee solubles were in how much water.

This is not quite Andy's brew ratio, since soluble yields figures in -- it's the puck's weight loss divided by the shot weight. When I did the research I kept this figure fairly constant regardless of the dose or solubles yield. This is very easy -- if you stop the shot at the same blonding point each time, regardless of how long it takes, you'll have roughly the same solids concentration in the cup.

Turns out this is probably wrong. If the solids concentration is kept the same, underextracted shots taste stronger than properly extracted ones -- the caramels have a mellowing effect. I happen to prefer hi-powered coffees that are undrinkable when underextracted, mellowed out by deeper extractions; but this is not everyone's cup of tea. Medium and medium dark roasts have more body than light roasts, even at the same solid concentration. I do not know the chemistry and organoleptics behind this.

[danblev]

Thanks Jim!

I have to confess that after reading this paper I see the light.

Smooth and well balanced espresso from a roast stopped just before second crack.
--
Danny

[another_jim]

Thanks for the praise.

However, my take is that the predominant opinion so far is that it's a useful tool for doing light SOs; but for normal espresso, the ding on body is too much.

Of course, I haven't begun to design and roast espresso blends for this technique yet

[appa]

Hi Jim,

Thanks for your time and effort in this reseach.

I have a couple of questions from a newbie perspective

1) you mention in your article that
"
In properly brewed coffee, about 18% to 22% of the ground coffee is dissolved into the water, while the rest is spent grounds; the range in espresso shots is wider, running from 15% to 25%
"

Is the distribution of solubles different in regular coffee different than in espresso (more or less heavy compounds,etc). I was under the impression that the solubles yield for espresso would be much higher cos the high pressure, etc.

2) How important is coffee freshness now considering the italian model of espresso making you mention in the conclusion?


Thanks again

[another_jim]

Is the distribution of solubles different in regular coffee different than in espresso (more or less heavy compounds,etc). I was under the impression that the solubles yield for espresso would be much higher cos the high pressure, etc.

The conventional wisdom before I did this paper was that a properly drawn espresso shot would be around 20% solubles yield. This was especially true if the shot was stopped at the proper point, when the color blonded. I believed this and stated it in my article on espresso on this site. I, and the conventional wisdom, were wrong. "Underextracted" and "overextracted" are judgement terms. When Abe was visiting me, he consistently preferred shots dosed around 1/2 to 1 gram higher than my favorite level, with extraction levels roughly 2% percent less. This was of very light (ultra-North Italian) roasts. Abe enjoyed the extra aromatics and flavor, while I preferred a little extra caramel. We both agreed how the taste change, but didn't agree on where the best balance was to be found.

2) How important is coffee freshness now considering the italian model of espresso making you mention in the conclusion?

I don't care how stale coffee extracts -- all the results I've quoted for my experiments and for brewing coffee are using very fresh coffee. The results given in academic papers on espresso do not mention how old the coffee was, or how it was preserved.

My intent in the conclusion was that the Italians, like almost all people, are not fussy about fresh coffee, so they could use dosers to precisely dose any weight of coffee they wanted. For people who are fussy about fresh coffee, dosing different weights does present a problem. Solving this problem by using 18 instead of 14 gram doses had the consequence, I think somewhat pernicious, of lowering the solubles extraction.

Thanks for pointing this ambiguity out. If an intelligent reader who has the courtesy to read something all the way through, misreads a point, the fault lies with the author's writing. I'll rewrite to make it clearer.

[appa]

Thanks again Jim,

I dont think this is ambiguity on your part as much as the actual audience
reading the paper may be larger than the intended target audience, but I think this
is a good thing for you

[Martin]

<<<snips>>>>
the actual audience . . .
reading the paper may be larger than the target . . .

I agree with this observation, but with some reservations. The actual audience may "get" more than what meets the eye in this thread. An interesting case in point can be found in this exchange on the La Spaziale users forum (I can't recall if you need to register to get in). Several of us are sharing some experiences on how Jim's findings are helping make sense of our experiences with the very wonderful, if idiosyncratic, La Spaz Vivaldi.

http://www.rimpo.org/wforum/viewtopic.php?p=2965#2965

I'd be interested in hearing from folks on this forum who have altered their shot-pulling practice and their thinking in response to Jim's article.

Martin

[appa]

Since reading the paper, i bought a scale and started downdosing,
until i was getting good consistent, doubles with only 14 grams.
Before I was probably dosing with 20 grams, with at least a few grams being flicked away
as excess. Knowing that now im getting the most bang for the buck is encouraging

Im still not sure if a finer grind with a smaller dose is more forgiving as far as technique goes,
since my technique still needs help,(holding off on WDT for now). My main challenge
now is that sometimes the coffee is way below the portafilter rim, making distribution a bit
of a challenge, it may be time to go to those curved swipers mentioned in the article...

[appa]

Forgot to add 2 more points:

1) now that Im down-dosing, my grind settings are much closer
to my mazzer mini's "zero-point", Coincidence? now Im thinking not,

2)my experience with the mazzer, and Martin's comments and thread above make
me wonder if Italian machines are "optimized" for a lower dosed, finder grind scenario.
Forgive me if this sounds ridiculous, I dont know much of the internals of machine design.

[another_jim]

One of the things people got which wasn't in the article was that headspace is a good thing on most machines. This is not about the depth of the puck per se, but how much room is left over it. There's two effects.
-- On many machines, the puck touching the shower screen degrades the taste, so these machines have a minimum headspace, or a maximum dose for each basket, depending on its depth.
-- More headroom makes for longer dwell times (it takes longer for that space to fill up, and the puck can swell more). Longer dwell times generally allow wider latitude on leveling and tamping.

In terms of the paper's thesis, that solubles yield, controlled by varying the dose weight to filter area ratio, systematically changes the taste, this is a confounding variable. I'd need variable height baskets each with the same hole area to get around it.

[Martin]

(it takes longer for that space to fill up, and the puck can swell more. Longer dwell times generally allow wider latitude on levelling and tamping.

This sounds relevant to arguments for or against pre-infusion. But how? Seems likely that the smaller diameter basket and relatively greater headroom on the La Spaz (at my current 15g) would factor into the machine not pre-infusing; or possibly its a reason for a machine like the Tea going with pre-infusion.
Martin