Cracking into the Extraction: when and where the espresso puck brews. - Page 2

Beginner and pro baristas share tips and tricks.
gscace

#11: Post by gscace »

another_jim wrote:-- What is surprising is that the bottom gets stronger. What is happening is that the ground coffee at the bottom is absorbing the overbrewed coffee from the top, and retaining this until the second half of the shot.
Jim:

The brewing temperature within the puck is dependent on radial and axial position within the cake. The bottom definitely heats up later than the top. Is it possible that the bottom also extracts at a slower rate in the beginning because it is colder than the top? Also the pressure near the bottom is near to atmospheric pressure, unlike the pressure at the top

I'm wondering whether these factors drive extraction rate more than concentration of solutes in the water as it passes through the bottom of the cake.

Interesting work. I wonder how this relates to basket geometry. My laSpaz, with 53mm baskets produce a different taste compared to the straight sided Faema double baskets that I use in my Linea. Brew parameters are otherwise equal in temperature and pressure at the top of the cake, although the pressure rampup may be slightly different (0.6mm gicleurs in the Linea and unknown in the Spaz).

-Greg

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another_jim (original poster)
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#12: Post by another_jim (original poster) »

gscace wrote: Interesting work. I wonder how this relates to basket geometry.
This and group head design is one of the things I'm working towards (the other being the grind). It seems to me if you have two espresso machines, shots from the same machine at slightly different pressures and temperatures generally taste more alike than shots from the two machines with pressures and temperatures adjusted to be the same. Machines and baskets seem to have a "style" of some sort.

In order to get at this, one needs to be able to see what's happening inside the puck. Interrupting shots and analyzing the partially spent pucks seems the obvious way of doing this. I'm also hoping to be able to organize a laser particle count/sizing on the same sequence of pucks.

The ultimate goal is to build time domain equations of the extraction for solubles with different solution rates. This will give an "extraction map" of the puck for each different tastes in an espresso (providing Lingle's Taster's wheel is right about the taste & molecular weight sequence). Pressure and flow maps can be inferred from the changing fines and coarse distribution, and we already have data on the temperature profile at various puck depths.
Jim Schulman

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cai42

#13: Post by cai42 »

Greetings,

I know temperature affects solubility. I don't know "beans" about bean constituents and their solubility but couldn't this be one of many factors going inside the puck? Higher temps at the top of the puck and dropping off as the extraction ends.

Cliff Isackson

King Seven

#14: Post by King Seven »

I wonder if the movement of the fines and other smaller particles affects things?

412Rich

#15: Post by 412Rich »

Taking all this into consideration, if you were to design a basket from scratch, would it be ridgeless or ridged similar to current models or something different?
Crazy Mocha
Pittsburgh, PA

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another_jim (original poster)
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#16: Post by another_jim (original poster) »

412Rich wrote:if you were to design a basket from scratch, would it be ridgeless or ridged similar to current models or something different?
I certainly would go either ridgeless or with outie, rather than innie, ridges. One upshot of these tests is that one may want to use the same basket for radically different doses: large doses, coarsely ground or small doses, finely ground. A ridge almost always screws up the levelling and tamping for small doses.

King Seven wrote:I wonder if the movement of the fines and other smaller particles affects things?
Fines is what got me started on this.

There's an old alt.coffee exercise of using three cups for a shot, putting the first few seconds in the first, the next few in the second, and the final part in the third. Unsurprisingly, the third section tastes weak, and slightly bitter. It's the first two sections that are puzzling: the first section tastes very intense, both bitter and sour; while the second section tastes sweet and creamy.

I always thought that the first section's taste was marked by overextracted fines. But the Illy chapter says the fines migrate down toward the bottom of the puck, and are necessary to control the rate of flow. Now, if you have a column of ground coffee, and send water through, the coffee will brew from the top down, since the water will extract all the top coffee, get saturated, and be unable to pick up solubles further down.

Bottom line: the fines brew faster, but are further down the puck; so when do they brew, into the first or second third of the shot? Turns out, it's in the second, sweet third of the shot, and that they may have been getting a bad rap.
Jim Schulman

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hbuchtel

#17: Post by hbuchtel »

I think that the 3-way valve is throwing off your measurements, can you repeat your test with the valve disabled and let the pucks 'drip-dry'? Or do the same test on your Peppina?

Henry

Decent Espresso: espresso equipment for serious baristas
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another_jim (original poster)
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#18: Post by another_jim (original poster) » replying to hbuchtel »

With all due respect; if you think the results are invalid, you should repeat the trials. After my initial trials, I thought about this; then some more after your first post. I see no reason to repeat the trials without a three way.

Puck concentration increases in the direction of flow. The three way pulls the liquids upwards. I immediately removed the puck, and left it upside down to drain a few minutes, keeping the liquids moving further towards the top. This will tend to move solubles towards the top of the puck and even out the readings. If you let the puck drain and dry in the PF, the liquid will move downwards, rather than upwards as in a 3 way, and the puck bottom will get even more solubles. That at least is my take. If you think my reasoning is wrong; repeat the experiment with your own protocol.
Jim Schulman

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hbuchtel

#19: Post by hbuchtel » replying to another_jim »

I hear you, I'm being an a**hole about it 'cause a lot of people are going to look at your graph and say "ah, this is how it is" ...

Besides causing the liquid in the puck to flow upwards the 3-way would also 'vacuum' off a bit (how much?) of coffee liquid. It could be exaggerating the difference between the three puck levels or it could be evening them out ... Allowing the puck to dry by itself also has problems, but at least it would provide another result.

As for me repeating the test, I don't have the skills (or a TDS meter) that would make my results useful ... so I'll just settle back in my armchair ;) but would you mind posting how you got the TDS results?

Going on the results so far, it would seem like the cone shape of a single basket should extract more evenly then a double basket.

Thanks again for doing the legwork!

Henry

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#20: Post by another_jim (original poster) »

Sorry to sound snippy. I post data from 2 to 3 experiments a year; and always get lots of suggestions on how I can improve them, and never, ever a volunteer to do the improved version.

3 way valves don't suck anything -- the burp discretely as they vent the built up pressure. In groups that hold a lot of water between the puck and the three way, they will spit a lot of water. The Semi has almost no storage inside the group, and the pressure is equalized with a tiny run-off. On low dose shots, water remains over the puck.
Jim Schulman