How to think about Pre-Infusion / Pressure Profiling

Beginner and pro baristas share tips and tricks for making espresso.
kantai
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#1: Post by kantai »

As the owner of a BDB, I'm fortunate enough to have the ability to engage in some fussing around with the machine's pre-infusion settings (and, if I so desired, unlock some full profiling functionality via modding). This machine is great -- I find that I'm able to produce great espresso from a wide variety of roasts (I tend to buy lighter roasts) and from both blends and single origin coffees. However, I don't think I really understand the trade-offs at work when it comes to pre-infusion settings.

Holding the pressure profile and temperature settings constant, optimizing grind size and yield ratios is relatively straight-forward: there's many helpful guides in the FAQs here, there's the Barista Hustle espresso compass, etc. My rough plan of attack is "Grind as fine as you can without causing excessive channeling or choking the flow, then choose a yield to balance the sweetness and the acidity."

Pre-infusion, however, adds a whole additional wrinkle. I try to roughly use pre-infusion to reduce channeling -- I fuss around with my pre-infusion settings (increasing pre-infusion time, reducing pre-infusion pressure) until I can see my basket is saturating evenly before the pump goes to full pressure. However, this is a variable that's difficult to separate from grind size -- so as I increase pre-infusion settings, I can decrease grind size, etc. I usually get to a point where I'm happy with my shot, but sometimes that's like half-way through a bag of coffee, and I never feel like I approached it in a very rigorous way.

I suspect that this is part of what is nice about "manual profiling" in machines like the Bianca or via modding the BDB -- you can change your grind size and then tune the pressure on the fly, very quickly getting the "right" pre-infusion settings for a particular grind level.

So my question is this -- is there a more rigorous way to think about pressure profiles or pre-infusion? If not, do you have any ideas on how to start to frame one? How do cafe's usually determine their pressure profiles for different beans?

jevenator
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#2: Post by jevenator »

I can't attest to how shops develop profiles. Probably lots of beans and trying lots of different combinations.

But for me I don't worry about it too much. I flow profile all my shots. I aim for the same thing usually. I find my pressure begins to rise about 8 seconds and I get first drops in cup around 12-14. I usually continue to let it bead and form for a few more seconds and then increase the flow to get a gentle stream. If I'm pulling shorter shots I won't taper the flow down and just turn off the pump but if I'm going for a longer shot then I will taper the flow down around 1/2 or closer to 2/3 of the shots target weight.

If I don't like it I will adjust the grind just a tiny bit to get the taste I want. PI is now part of my routine and I taught my wife to do it as well for her lattes to not fuss with the grind settings because I grind pretty fine.

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Peppersass
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#3: Post by Peppersass »

I have a GS/3 AV that I modified to do flow and pressure profiling. It uses a variable speed gear pump and a high-quality line pressure regulator.

I tend to drink light and medium-light roasts, and sometimes medium roasts. I only use flow profiling for the lightest roasts, and then only when I can't pull a balanced shot without flow profiling.

I start dialing in a new roast by setting the grind to produce a 1:2 Normale ratio in 30-35 seconds. If it's too sour, which is often the case with light or medium-light roasts, I'll go finer with the grind. With roasts that are on the lighter side I'll gradually reduce pressure after peak to maintain a constant flow. It's a judgement call where exactly to set the constant pressure on the back end of the shot, which in turn affects the shot duration (contact time) but typically I set it to about 25-30 ml/min for a single and about 50-60 ml/min for a double. Most shots I pull this way finish in the 40-50 second range.

If I get to the point where I can't go any finer without choking the machine, and the shot is still sour, I'll pull longer -- i.e., a little Lungo -- to see if that helps. The tradeoff is a less syrupy mouthfeel.

If Lungo doesn't do the trick, I try flow profling. My setup for flow profiling isn't ideal. For various reasons I don't use a needle valve, at least yet, so what I do is lower the line pressure to about 1-2 BAR, which when the 3-way is open and the gear pump is turned off results in about 15 seconds to preinfuse a VST double basket. That's similar to the nominal needle valve setting recommended by Slayer. The downside to my setup is that I can't slow the flow rate any lower because the gear pump will cavitate when the line pressure gets too low. Anyway, the preinfusion allows me to grind super fine. Usually I run the shots pretty long, as much a minute or more, including preinfusion time. Flow profiling tends to make the flavors pop more than a standard pull. Sometimes that's good, sometimes not.

As I said, I don't flow profile all that often. I find that a little more work with the grinder, pressure and time tend to work fine for all but the lightest roasts.

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mohninme
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#4: Post by mohninme »

kantai wrote:So my question is this -- is there a more rigorous way to think about pressure profiles or pre-infusion? If not, do you have any ideas on how to start to frame one?
Oh so many variables with PI and profiling...It gives me a headache sometimes... or is that an overdose of caffeine?
With a new coffee, my initial approach is always to dial in a standard shot at a 2:1 yield targeting low 30 seconds. I will use that as the starting point and then adjust from there. Pepperass does similar. I also sometimes do long PI shots amounting to 60-80 seconds overall with lighter roasts looking for the sweet spot.

I recently experienced two ends of a spectrum. I worked with a new to me coffee over this last weekend and it just wasn't doing it for for me in the cup. I went to the extreme and ground it super fine, PI for 35 seconds and pulled a 3:1 yield over about 70-75 seconds and it finally raised my eyebrows. The previous week I was taste testing a new roast for a local roaster. It is a pretty standard espresso roast with nice chocolate notes and doesn't really need any PI. Well my setup is all pretty manual and you need to pay attention when your driving. I got distracted and gave it about 12 seconds PI and had to really throttle back the flow as the puck wasn't holding up. I was completely stunned when I tasted it and found a flavor of over ripened pineapples that wasn't anywhere to be found previously. Okay so whats the point of my ramblings.... There are some basic rules and some of, you can expect it to do this when you change that... but really its all fair game. I try to note what I have done, but not to over analyze, experiment lots, have fun and let my taste buds be the judge.

I know the feeling about going through a half bag, maybe more, before I have achieved something I am satisfied with in the cup. It sounds like you have a pretty good handle on what to expect for results when you change a variable. I really enjoy the process, so I just count it as a cost of the hobby. I always buy 2 lbs/2 bags. One thing I have done to help with burning through beans is move to a lower dose basket (15g in my case) and that preserves more shots per lb of beans.
Michael

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Peppersass
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#5: Post by Peppersass »

mohninme wrote:One thing I have done to help with burning through beans is move to a lower dose basket (15g in my case) and that preserves more shots per lb of beans.
And the lower you dose, the finer you can grind, and that can help with light roasts. It's one of the reasons I drink singles almost exclusively these days.

pcrussell50
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#6: Post by pcrussell50 »

Excellent sound barista advice as always, Dick. Sounds like when you want a finer grind, you choose to down-dose first, and then if that doesn't work, resort to long PI.

Nothing wrong with down-dosing to compensate for finer grinding of course. That is a long standing barista skill. However with control over flow and pre infusion you don't have to down dose when you grind finer. I suspect that's the whole point of having such control. Or at least it is for me. With flow control, I rarely make dose adjustments any more.

-Peter
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Peppersass
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#7: Post by Peppersass »

I probably wouldn't resort to downdosing if my preinfusion setup was easier to use and offered more flexibility (i.e., if I had a needle valve!)

That said, I also drink singles because they taste better to me and I feel the reduction in caffeine has been beneficial.

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kantai (original poster)
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#8: Post by kantai (original poster) »

mohninme wrote:I know the feeling about going through a half bag, maybe more, before I have achieved something I am satisfied with in the cup. It sounds like you have a pretty good handle on what to expect for results when you change a variable. I really enjoy the process, so I just count it as a cost of the hobby. I always buy 2 lbs/2 bags. One thing I have done to help with burning through beans is move to a lower dose basket (15g in my case) and that preserves more shots per lb of beans.
Yep, I definitely enjoy the process of fussing around with beans, and I'm definitely always happy to get a dozen different kinds of shots out of a bag. I don't mess around with dose (or singles) too much, since there's other baristas involved who will enthusiastically grind, tamp, etc., so long as they are weighing out a 18g dose every time, and can just hit a button on the machine to get their double (also why my BDB will remain unmodded!).
Peppersass wrote: If I get to the point where I can't go any finer without choking the machine, and the shot is still sour, I'll pull longer -- i.e., a little Lungo -- to see if that helps. The tradeoff is a less syrupy mouthfeel.

If Lungo doesn't do the trick, I try flow profling.
Interesting! This is pretty similar to what I have been kind of randomly doing, but thinking through both your reply and mohninme's reply leaves me with some sort of structure:

1. Sourness can be balanced by increasing yield, or by grinding finer (which increases the range of "good" yield ratios-- on the Barista Hustle espresso compass, that's moving up and to the left).
2. Grinding finer can lead to choking/channeling, so you can use PI to balance that, by aiming for full saturation in the bottomless filter before moving to full pressure. However, the idea isn't to target some ideal pressure profile and then try to grind to meet that. Instead, the grind that you use sets the pressure profile requirements.

So a process for tuning PI might be:

1. If your normale is sour, try a lungo (with the mouthfeel trade-off that implies).
2. If the lungo is still sour, grind finer and try a normale.
3. Whenever you change grind, re-time the PI for full puck saturation.

Rinse and repeat.

Fortunately, the BDB does have an undocumented manual pre-infusion mode --- if you set PI to 0 seconds, and hold the manual shot button, it holds the shot in PI until you release the shot button. That way you can figure out how long to set the PI to, allowing other baristas to reap the rewards of tuning :D

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mohninme
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#9: Post by mohninme »

Peppersass wrote:And the lower you dose, the finer you can grind, and that can help with light roasts. It's one of the reasons I drink singles almost exclusively these days.
This was more of a general comment in moving to a smaller dose basket to help with bean-burn (not specific to down-dosing, but you are correct on the correlation between down dosing and grind fineness). I have not bothered going down to a 7g single as I don't usually drink straight espresso. My preference being a low volume long black or americano.
Michael