Why Does a Long Pre-Infusion and Extraction Work?

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cskorton

#1: Post by cskorton »

Hi All,

I'm hoping to receive some insight into why I pulled an amazing shot this morning but I can't figure out why it worked.

Coffee: Passenger Daterra, a medium roast (I think) https://www.passengercoffee.com/products/daterra

Tasting Notes/Body: Very sweet; Pronounced Red Berry with Cocoa Finish, just like the bag says; Good medium Body

Brewing Equipment: Londinium R and Kinu m68; 18g VST Basket

Brew Parameters: Pre-infusion pressure: 3 bar for 20 seconds (until first drops); Brew time at full pressure: 45 seconds; 18g in 34g out

Synopsis: The above was this first shot I pulled when trying to dial it in and I found it having insanely sweet taste with pronounced, layered, and nuanced flavors as described on the bag. I'm wondering how this is possible so I can adjust brewing parameters for other coffees to get the best out of each bean.

My expectations of this first shot would have been very bitter because I thought the grind was too tight. I then pulled a second shot using a more traditional profile: 10 second preinfusion, 28 second extraction at full pressure by grinding coarser. This second shot tasted pretty bad, too sour and astringent. But, it visually looked better. The bottom of the basket looked more even then the first shot.

Maybe following traditional brewing parameters don't always work? I want to be able to use the lessons learned on this bean to others so I can get the best out of each coffee. Are there general parameters/guidelines that I'm not aware of? I don't want to stumble upon really great tasting shots by accident to avoid wasted coffee. What kind of coffees/roasts would this profile work well for/not work well for?

Thanks!

Jeff
Team HB

#2: Post by Jeff »

The Passenger coffees that I've tried have generally been medium-light or light. Lighter-roast coffees tend to be harder to extract than darker roasts. Grinding finer helps by providing easier paths for the water to extract the goodness. If the greens and the roast are good, it's hard to "over-extract" them. I usually pull light roasts at 1:2.5 or 1:3, or sometimes even longer.

If you go too fine with a standard profile, you're likely to choke the machine or cause excessive channeling. The long soak helps soften the puck and give it more integrity during extraction.

What you describe works well for me for medium-light and lighter beans, and some medium. I find that extended PI or soak usually brings out bitter flavors I don't enjoy from some medium and most medium-dark roasts.

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baldheadracing
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#3: Post by baldheadracing »

cskorton wrote: Brewing Equipment: Londinium R and Kinu m68; 18g VST Basket
...
Maybe following traditional brewing parameters don't always work? I want to be able to use the lessons learned on this bean to others so I can get the best out of each coffee. Are there general parameters/guidelines that I'm not aware of? I don't want to stumble upon really great tasting shots by accident to avoid wasted coffee. What kind of coffees/roasts would this profile work well for/not work well for?

Thanks!
On my levers, I find the most difference in pre-infusion pressure - I generally use
either dipper pressure (around 1.3 bar) or line pressure (around 3 bar). I generally grind fine enough to get about a 30 second pre-infusion (to a fully wet basket bottom), and extract for about another 30 seconds after that. (The lighter the roast -> the lower the pre-infusion pressure, most of the time.)

Keep in mind that I am not working in a bar so I care more about flavour over speed, and I am pulling single-farm/collective/washing station high-grown coffees, albeit not super-light cupping/sample roasts.

I will grind coarser and pull the more normal 10 second pre-infusion, etc., with darker roasts and also 'punches through milk' conventional espresso blends.

Or, to put it another way - and get a better explanation :oops: - I do more-or-less what the decent machine folks have as the 'lever' and 'blooming' "mother recipes" (go to post#165) :
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cskorton (original poster)

#4: Post by cskorton (original poster) »

Thank you both for your responses. I found that decent thread to be extremely helpful, especially John's videos.

I find it interesting that for light roasts you use lower preinfusion pressures, which seems to be the opposite of Reiss's suggestions over at Londinium. I'll have to give it a shot, I automatically run lighter roasts at 3 bar preinfusion pressure.

Also, is there any logic as to how long preinfusion and full pressure should last? I used to push full pressure to 30 seconds after a 15 second preinfusion, but I'm finding keeping it much shorter, around 20 seconds, has been working better with longer preinfusions.

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baldheadracing
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#5: Post by baldheadracing »

I'm sure Mr. Gunson knows what works best for his machine's technologies.
What I'm interested in is my worst espresso being fantastic - James Hoffmann

Jeff
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#6: Post by Jeff »

One thing to remember is that while the basket is filling, there is effectively no pressure. "Pressure" is meaningful then only in terms of the restriction that is limiting flow into the basket (often a gicleur, or tiny hole is the primary restriction). Higher pressure from the pump leads to a higher flow rate into the basket. Once the basket is full, then pressure takes meaning and will, along with the condition of the puck, determine flow.

There are no "rules" once you move past conventional espresso blends. Timing for a Kenyan or Ethiopian will likely be very different than a Central American coffee. The Ethiopian will likely be different than the Kenyan during extraction. The quality of greens and roast will determine how far you can extract before the defects start to become noticeable.

Some of my shots with light roast coffees run 45-60 seconds total. It all depends on what tastes good that day!

cskorton (original poster)

#7: Post by cskorton (original poster) »

Thanks! Yeah, I guess I'm trying to better understand the why vs the how as far as brewing parameters go. Questions like how long preinfusion? When to know to increase/decrease it? Same goes with brew time, and various pressures. For example, for roast level x and bean type y initially try brew profile z.

I know it's an impossibly complex and deep question, but what I'm trying to do is minimize bean waste so I'm not burning through a half a bag of beans in a day or two trying to optimize taste.

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Peppersass
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#8: Post by Peppersass »

It's a good question, or set of questions, but there are no easy answers. For me, it's taken years of trial-and-error with many different coffees/roasts. And I'm still learning!

Before gaining experience with PI, I used to start by pulling the coffee with "standard" espresso extraction parameters. On my machine, a highly-modified GS/3 that can do flow and pressure profiling, that means not using the flow control mods and relying instead on the the machine's inherent PI flow rate. That's a ramp from zero to 9 BAR in less than five seconds. I let the shot run for 25-35 seconds to produce a 1:2 brew ratio.

If the shot was under-extracted, and the roast was medium, grinding finer would often get a full extraction. But if the roast was light or medium-light, grinding finer often would not fully extract. If I kept grinding finer and finer, either the machine would choke or the shot would get less extracted (more sour) due to to many fines.

That's the point at which I'd start increasing the PI time. Normally, I set the PI flow rate to about 100-120 ml/min, which is what Slayer recommends. If the roast is light-medium, I'll probably start with a PI time of 10 seconds or so. If it's a light roast, I'll probably start with 15 seconds or so. I usually don't go higher than 22 seconds of PI time.

Regardless of whether I use long, slow PI or standard PI, I always ramp down the pressure after peak pressure is reached in order to maintain a constant flow rate. For a double, that would be 50-60 ml/min. For a single, it's 20-30 ml/min. If the pressure isn't ramped down, the flow rate will keep increasing. By holding the flow rate constant, the contact time and extraction are maximized. It's rare to find a true medium or lighter coffee than can be over-extracted.

Nowadays, I can usually make the PI decision based on the roast color, rather than pulling a standard shot first. The color determination is based on what the roaster marked on the bag or what I was shooting for with my own roast, plus eyeballing the bean surfaces and measuring with a roast color meter. Currently I'm using the Roast Vision (read about it here.)
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baldheadracing
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#9: Post by baldheadracing »

cskorton wrote:Thanks! Yeah, I guess I'm trying to better understand the why vs the how as far as brewing parameters go. Questions like how long preinfusion? When to know to increase/decrease it? Same goes with brew time, and various pressures. For example, for roast level x and bean type y initially try brew profile z.

I know it's an impossibly complex and deep question, but what I'm trying to do is minimize bean waste so I'm not burning through a half a bag of beans in a day or two trying to optimize taste.
The first thing that I'll do with a new (purchased) coffee is cup it and measure TDS and EY against whatever other coffees I have around. I typically have a couple of my own roasts going (plus a decaf). From there I'll have a pretty good idea of where to go, what characteristics I want concentrated in the espresso, what characteristics I want to mute, etc. For the first few years I kept copious notes, but I rarely look at them now.

I'll chose one of the four (well, three) general approaches based on roast level that I linked to above - as I don't have a decent, that's essentially deciding which machine I'll use - and then I'll usually follow Dialing in espresso by Gwilym Davies [short PDF]
What I'm interested in is my worst espresso being fantastic - James Hoffmann

Jeff
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#10: Post by Jeff »

A lot of it seems to be what controls you have on your machine, or what machine you pick among your choices. I think the common things are

1) Fill the basket; some like faster, some like slower (Peppersass' approach sounds like the "slower" at ~2 ml/s)
2) Hold at a moderate pressure (1-3 bar?) for "a while"
3) Make a decision that the puck seems pretty well soaked (more than a couple drops falling is a common indicator)
4) Increase to an extraction pressure that gets a flow rate that is appropriate for the coffee, your grinder, and your preferences
5) Ramp down the pressure to keep the flow rate where you want it

#5 is still something of voodoo or religion. I think that "constant flow" is something that emotionally feels good, but I haven't seen any well-controlled studies that say that it is "best". My personal experience is that a "flat, 9-bar" profile doesn't taste as good as a declining-pressure profile (with reasonably constant flow in the later portions), to me, with my coffees, my tastes, and the grinders and machines I've used, both pump-driven and lever.

Since sometimes a picture is clearer than words, here's the first shot from a bag of Guatemala El Injerto, wet-process fermentation, Linea roasted to medium-light as measured by the same gizmo Dick uses. (You definitely don't need one of these. I bought one so I wasn't guessing about roast level when I made comments. I've got good "working definitions" for medium-dark, dark, and burnt, but medium through light and ultra-light is something my eye isn't good at yet.)





Here's a walk-through of the DE1 chart. The green line is pressure in the basket, left-side scale. The blue line is flow into the basket, right-side scale. The brown line is mass-flow into the cup, right-side scale.

1) 0-7 seconds -- basket filling at ~6 ml/s, rising pressure in the basket indicates that the basket is pretty full
2) 7-25 seconds -- basket holding at 2-3 bar, bottom of the basket is wet, but not dripping
(a "2-3 bar PI pressure" would probably do something similar to the above two steps)
3) 25-27 seconds -- first drops start landing in the cup
4) 27-30 seconds -- pump raises the pressure to my desired 6-bar extraction pressure; the spike in flow (blue) is probably due to the puck compressing
5) 30-42 seconds -- flow rate starts increasing as the puck starts eroding (the pressure is constant, the puck's "resistance" to flow is decreasing)
6) 42-55 seconds -- pressure backs off to try to keep the flow rate in my target of around 2.5 ml/s for this style of shot

If I pulled a dark roast the same way, I'd probably have the distinctive flavor of a '57 Chevy ash tray in the cup.



88°C is a pretty typical temperature for a DE1. It measures temperature in the basket, rather than that of the water entering from the boiler. There really isn't a one-to-one, but 88°C is sort of the equivalent of the canonical 201°F.