Extraction, roast degree and extraction yield

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mathof

Postby mathof » May 15, 2018, 11:55 am

I have read many times that light roasts are harder to extract than darker ones. I've been using relatively light beans for espresso for some time now, employing Matt Perger's methods for dialing in. My usual extraction yield (EY) has been between 19 and 21 percent. Recently, however, I have employed a number of darker beans, roasted medium/dark. To my surprise, these are the ones that are harder to extract. I find my extractions with them measure more frequently in the 16 to 18 percent range. Can anyone explain?

Matt

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Peppersass

Postby Peppersass » May 15, 2018, 4:05 pm

Did you change the grind setting, dose, brew ratio or shot time for the darker roast?

samuellaw178
Team HB

Postby samuellaw178 » May 15, 2018, 4:23 pm

Another possibility could be the darker roast was not developed evenly, with the inside of the beans being less 'cooked' than the outside. Do you see any sign of that?

I indeed find that with medium/darker roasts it's generally very easy to get gloppy, syrupy pull and a high TDS% with a short shot.

mathof

Postby mathof » May 16, 2018, 4:30 am

Peppersass wrote:Did you change the grind setting, dose, brew ratio or shot time for the darker roast?


I use the same dose for everything: 15g in a 15g VST basket
I use the same brew ratios for everything: 30g out for 5oz milk drinks; 32g out for straight espresso
I do change grind settings to achieve flow ratios between 25 and 40 seconds (from beginning of flow)
I do vary pre-infusion times and lever action (eg Fellini)

Matt

mathof

Postby mathof » May 16, 2018, 1:19 pm

samuellaw178 wrote:Another possibility could be the darker roast was not developed evenly, with the inside of the beans being less 'cooked' than the outside. Do you see any sign of that?

I indeed find that with medium/darker roasts it's generally very easy to get gloppy, syrupy pull and a high TDS% with a short shot.


The beans I am using at the moment - Columbia Suarez roasted med/dark by Rave in the UK - look fine when cut open.

I can get a higher TDS, and a much lower EY, by pulling a ristretto, but I don't favour that kind of shot.

Matt

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another_jim
Team HB

Postby another_jim » May 16, 2018, 2:50 pm

mathof wrote:I do change grind settings to achieve flow ratios between 25 and 40 seconds (from beginning of flow)


So what's the mystery? Coarser grind settings lead to less extraction.

Another question is whether there even is a problem. Darker roasts get bitterer at high extractions, whereas light roasts get mellower.
Jim Schulman

mathof

Postby mathof » May 16, 2018, 4:11 pm

another_jim wrote:So what's the mystery? Coarser grind settings lead to less extraction.


In fact, darker roasts do require coarser grind settings for similar timings. I've noticed that, but I've never been able to figure out why it should be so.

Another question is whether there even is a problem. Darker roasts get bitterer at high extractions, whereas light roasts get mellower.


That's an interesting observation. I don't suppose there is a problem.

Thanks,
Matt

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another_jim
Team HB

Postby another_jim » May 16, 2018, 6:23 pm

mathof wrote:In fact, darker roasts do require coarser grind settings for similar timings. I've noticed that, but I've never been able to figure out why it should be so.


I think there's a general rule that the more brittle the bean, the more fines you get grinding, and the coarser you need the grind to be to get the same flow (i.e. the amount of fines controls the flow rate). I also think beans are at their most brittle at the start of the second crack, a medium dark roast. When you get really dark, the oil (I'm guessing) softens them. And for some reason I don't know, Sumatra coffees produce fewer fines and meed finer grind settings.

Fines get a bad rap when people talk about grinding; but without them, there is no espresso.
Jim Schulman

Tonefish

Postby Tonefish » May 16, 2018, 6:36 pm

another_jim wrote:Fines get a bad rap when people talk about grinding; but without them, there is no espresso.

Please say more as there must be a subtlety here since even if every coffee particle were ground to identical size one could find a size that met espresso making parameters.
LMWDP #581 .......... May your roasts, grinds, and pulls be the best!

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another_jim
Team HB

Postby another_jim » May 16, 2018, 9:32 pm

In traditional espresso, there's a lot going on in a puck: the downward migration of fines, the correlated downward dissolving and redeposit of coffee solubles, the physical changes in the puck over the course of a shot.

So the only subtlety is the question of what is espresso. Take the new style of very lungo shots, using very light roasts, ground to a Turkish grind, with very little crema or emulsified fats; are these really espresso, or just a very capital intensive Scandinavian cafe crema? If the dynamics of the puck over the course of the shot is a part of the definition, these drinks are not espresso. They are something new.
Jim Schulman