Pressure profiling, flow profiling, and a new rule of thirds - Page 6

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#51: Post by yakster »

The pressure/flow reminds me of time domain (oscilloscope) versus frequency domain (spectrum analyzer) in communications, their relatable via Forier transforms.

LMWDP # 272

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#52: Post by Peppersass »

shadowfax wrote:I'm brewing Rwanda Dukunde Kawa and Kenya Thiririka Farmer's Cooperative this weekend. They're not the lightest roasted of coffees, but definitely far from an espresso roast.
For the past two days I've been trying Nicholas's method with Terroir's Yemen Mocha Haraaz, roasted five days ago. This was a limited roast intended for brewing.

I've never tried a high-end coffee from Yemen and have to say this is one of the best specialty coffees I've had (it should be -- it's one of Terroir's most expensive coffees!) Terroir describes the Mocha Haraaz as "wildly spicy", with raisin, grape, banana and even lily notes. Opening the bag, I caught the spice (though wouldn't call it particularly wild) and definitely got a strong aroma of raisin. The rest was sort of fruity, but I couldn't clearly identify it as grape. I could convince myself there was a slight banana overtone, but I smelled no lilies. I'm sure that's more a shortcoming of my nose than the coffee.

Before experimenting with the Mocha Haraaz as an espresso, I brewed it in my vac pot. Parameters were 18g dose, 250g brew water, ~200F, 35 second steep time, total contact time through drawdown of 1:45. First try was a little over-extracted, around 22% extraction yield, but I actually preferred that cup to the second try at 20%, which required going one macro notch coarser on the Vario (with metal Ditting burrs.) Though there was a slightly more bitter overtone, the flavors were more distinct in the first cup, especially when it cooled. I'm not a talented taster. Generally I can smell and taste fruit flavors in natural-processed coffees, but I can't always identify them. In this case I could taste the spice and distinct raisin overtones. I tasted fruit, but like the aroma from the bag I couldn't positively identify it as grape. No bananas or lilies in the cup, but again that's probably my pedestrian taste buds.

Next, I tried pulling a 9-BAR espresso shot at 200F with my usual parameters: 18g of coffee producing 28g of beverage in about 30-35 seconds. To get the right flow rate, the Mocha Haraaz required a much tighter grind setting than the espresso I'm currently pulling, which is Terroir's Borboya II. I had to go down three steps, which is a lot on my K10, and even then the balance was off -- quite sour. I didn't need to take an extraction yield measurement to know that the cup was under-extracted. One more step on the grinder definitely would be in order, but I didn't try that due to lack of time. I also didn't try a slow pressure ramp-down, which sometimes tames sourness in light-roasted single-origin coffees.

Next, I tried Nicholas's method by setting the gear pump motor speed to zero and preinfusing at the lowest line pressure possible, which in my system is 1-2 BAR. I let the preinfusion go until the pressure started to rise and I could hear the tell-tale "whistle" that usually accompanies a fully pressurized basket. That took 6 seconds or so. Then I let the shot continue without pump/motor assistance for about four more seconds. Pressure was around 3-4 BAR. Then I slowly cranked the motor speed up until the pressure hit 9 BAR at just about 18 seconds. Within a second or two the first drops of coffee appeared at the spouts. Then I let the shot run until I had 28g of beverage in the cup and the flow was just past the point of thinning and becoming convex (dual spouted portafilter) and the color was lightening. Shot time was 49 seconds. Brew temperature was 203F.

Like I've found with espresso roasts, I had to set the grind about four notches below the grind required for the 9-BAR shot. But the results were not the same: the shot was decidedly sour. It was a lot like the 9-BAR shot, only more intense. It wasn't completely unpleasant, and the shot was drinkable (barely), but it wasn't well balanced and I couldn't detect any of the flavors I tasted in the brewed cup -- they were simply overwhelmed by the sourness. It might have made an OK latte, but I didn't try that. Also, I didn't measure the extraction yield because the cup was so far off I didn't need any help deciding that it was very under-extracted.

I'm sure I'd have to grind much finer to tame the Mocha Haraaz for espresso. Unfortunately, that would have extended the shot time well past the GS/3's limit of 50 seconds. For the next attempt, I'm going to try a lower dose, probably around 14g-15g. It's possible that a much higher brew temperature will help, too, but I think it makes more sense to try the lower dose first.

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#53: Post by JohnB. »

5 days rest is pushing it for any Yemen you are using for espresso, particularly one roasted for brewing. Try it again in the 7-10 day range & see how it goes.

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#54: Post by indend007 »

Peppersass, maybe you'll need to more finer grind with fully soacking phase.
I have very good or acceptible flavor and well banaced cup from some beans which roasted for filter brew.
I always make a starting brew point after more second(least 10 sec) whistling, usually aiming to phase that full filled bottom area of basket and drops few ml(3~5ml?), it also looks like that slayer's pre-brew acting to do.

Maybe as you wrote, it telling other factors in origins of beans. I'll also do more extraction with light roasted bean for filter brew, and check the flavors and extraction through refractor meter.

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#55: Post by Peppersass »

JohnB. wrote:5 days rest is pushing it for any Yemen you are using for espresso, particularly one roasted for brewing. Try it again in the 7-10 day range & see how it goes.
I did and you were right -- I just tried it at day 11 and it was a whole different experience.

The first indication of a difference was the aroma from the bag -- much, much more berry. I still wouldn't call it "grape". It was more like blueberry, but probably that's a function of my ability to identify flavors. That said, blueberry is the predominant aroma I've been able to identify in other DP naturals. There was less raisin in the aroma, too, but maybe that was because the berry aroma was amplified.

Brewed in my vac pot (again, 18g coffee in 250g water), the berry flavor was much more forward than it was last week. Got a very enjoyable, nicely balanced cup with beautiful aroma and flavor, which got even better as the cup cooled.

I lowered the espresso dose to 15g and pulled a 28g cup in about 30 seconds at 9 BAR at 200F. This time the cup was much more balanced, and the berry aroma/flavor came through.

The cup was still a bit under- extracted, so I tried the same dose/grind and brew ratio, but slowly ramped down the pressure a few seconds after reaching the peak at 9 BAR. That extended the pull time to about 35 seconds, which tamed the sourness enough for me to pronounce the cup very good.

Finally, I tried Nicholas's method. I bumped the temperature to 203F, tightened the grind four notches on the K10, preinfused at 1-2 BAR for about 8-10 seconds, then slowly ramped the pressure to reach 9 BAR at about 18 seconds or so. First drops appeared at 20-22 seconds, and the shot ran for a total of 45 seconds. The resulting cup was very well balanced and much, much brighter without being sour. The berry flavor was quite a bit stronger that the previous two pulls. Very enjoyable cup.

As I slowly sipped both the last of the vac pot cup (quite cooled by then) and the last espresso pull, I was amazed by how similar they tasted. The only difference was the intensity, which was of course much greater in the espresso cup. I would say this is the closest I've ever come to tasting essentially the same flavors in a coffee brewed in my vac pot and prepared as espresso.

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#56: Post by another_jim »

That's my personal ideal for a great espresso shot too (other people have other ideals). Now if only there was a straight forward technique for getting there. Instead it seems, there's lots of experience, trial and error required for every different coffee.
Jim Schulman


#57: Post by jonr »

Referring back to early posts regarding why slow ramp up makes so much difference on later flow, note that people who compress soil know that the moisture content of the soil greatly effects how much it compresses with a given amount of pressure. Ie, wet then compress is very different than compress then wet. And it's a U shaped curve, not a flat line. But who knows, maybe with espresso it's about fines migration.

The resistance of the bed is not fixed (for example, note what happens to flow as you go above 10 bars or as you reach the end of a shot). So flow and pressure are not interchangeable (or at least not in any simple way).

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#58: Post by shadowfax (original poster) »


I've been thinking about this a little bit and I am not sure I understand what your point is regarding the compressibility of dry vs. wet soil and the suggestion that coffee exhibits the same phenomenon (which seems highly plausible). What does this have to do with the flow resistance that the coffee provides under resistance? It seems to me that regardless of the initial flow rate and pressure ramp, when flow begins on a properly prepared shot (i.e., one that doesn't have visibly uneven flow), the puck has become completely saturated. But the resistance provided is significantly different.

This may or may not be due to fines migration, but I don't understand what it has to do with the compressibility of wet vs. dry coffee. To wit, how does compressibility relate to flow resistance?
Nicholas Lundgaard


#59: Post by jonr »

> how does compressibility relate to flow resistance?

More compression creates higher resistance.

My point is that if you quickly apply 9 bars of pressure to a dry puck of coffee, it will permanently have higher resistance (ie, it will compress more) than a puck where you first apply water at low pressure until it is completely wet and then apply 9 bars of pressure. This is consistent with "pre-infusion requires a finer grind".

I suspect it is a case of water surrounding individual grains of coffee and then resisting compression.

How this all relates to better espresso or better machine design is an open question. But I'm pretty comfortable saying that pressure and flow vs time (ie, pressure and flow profiling) significantly effect taste.