Looking for a Simple Measure of Preinfusion - Page 9

Beginner and pro baristas share tips and tricks.

#81: Post by JayBeck »

TomC wrote:I haven't seen dosing mentioned too much in this thread. It's a fascinating discussion nonetheless. I'd imagine whatever device you're using to extract from, having a coffee "cake" right up under the dispersion screen would drastically alter your measurements. Not having a void above the surface of the coffee prior to saturation might change everything you're putting under the microscope.

I'm having the most fun studying the DE1 Pro, and aiming to have fully filled baskets and less headspace.
What's your typical dose? I've been getting updosing 2g for now. 20g in 18g VST. Seems to be a good starting point.

User avatar
Team HB

#82: Post by TomC » replying to JayBeck »

I've mainly been using 20.5 in a 20g VST of well developed stuff like Kimbo, Caffe Lusso, and Grafeo's. When I unlock the pf, the puck has swollen above the rim. I'd go even higher if I was using brighter, lighter roast coffees, but likely in a smaller basket.

I don't want to derail the purpose of this thread, but my main point previously is that dose clearly alters PI.


#83: Post by JayBeck » replying to TomC »

This is helpful and I totally agree regarding dose. In a fixed / non preinfusion system, does isn't very important other than using it to regulate desired grind size. In a complex preinfusion system (Bianca, DE1, GS3/MP, etc) then I'm finding dose makes a HUGE difference as it isn't necessarily impacting flow but it certainly impacts the preinfusion time (time to fill headspace, etc).

And how this ties back into the thread: Measuring the point at which 5g are in the cup as the end of preinfusion is likely the most consistent way to say that flow has really begun. I've gotten drops in the cup at 20 seconds but it may take another 10-20 seconds before a steady flow is coming out.

User avatar
Team HB

#84: Post by Jake_G »

Measure time to full pressure on puck, and time to first drops or x number grams in cup. Express preinfusion as the difference between those two times. Positive numbers reflect complete preinfusion and duration of soak or steep. Negative numbers reflect incomplete preinfusion, with longer numbers reflecting a longer dwell and perhaps a choked shot.

Nerd stuff below:

I've been cogitating over this subject for quite some time, trying to decide if there is a definitive, simple measure of preinfusion. As I look over all the responses and all the variables, I've come to a few simple points that I think are helpful, but not conclusive.

First, the whole shot, from pump on to pump off, is infusion.

Second, the part of the shot where stuff is exiting the basket is extraction.

There are the obvious caveats, such as the fact that any infusion into the top layer results in extraction of that layer into those beneath it, so in this way "pre" infusion loses its validity. But even so, we're left with what happens between when the infusion begins and the extraction into the cup begins. Suffice it to say that if preinfusion can be measured, it's in this time.

So then you are left with the question of whether or not preinfusion happened (it did), and if it finished before the extraction began. I agree with Assaf that you always get some preinfusion, whether you like it or not. This conversation has hit on all the relevant variables: grind, dose, headspace, flow rate, pressure, etc... so the follow-up, is "What do we do with all that?". I think the meaningful relationship of all of this is whether or not the basket shows coffee seeping through before the puck sees cake-crushing brew pressure above it. If it does, preinfusion was complete. If the pressure builds before the water makes it through, preinfusion happened, but it didn't finish.

The extent to which it didn't finish may matter and may tell a story about the rest of the shot. The extent to which it did finish turns into "How long did you keep passing water through the puck without pressure?" Or "How long did you steep or soak the puck?". Watching the bottom of the basket, it's easy to see when the headspace fills and the basket deflects as pressure builds. The time when this happens is half of the preinfusion story. The other half is when the basket wets. These 2 numbers give you the simple measure. "Pressure rise 4 seconds after first drops" to me is more meaningful than 15 seconds to first drops. Or 25 seconds to 5g in the cup. Likewise, "Pressure rise 26 seconds before beading " is way more meaningful than first drops at 32 seconds.

Note that the first example had complete preinfusion and a gentle, but not drawn out start, whereas the second shot was all but choked, and likely indicative of Bret's long and slow shots of Malabar Gold with "high pressure preinfusion", which I'd argue isn't a thing ;). It doesn't mean they're good or bad shots, but they're decidedly different in their execution. One has a positive PI measure (drops or beads or grams in cup before pressure). The other has a negative PI measure (pressure builds and then we wait for drops).

See any glaring issue with this? Obviously you can't measure it without a puck pressure gauge or a bottomless portafilter to see when the basket deflects, but it's really the answer to how much PI was present in a given shot. The rest of the normal shot parameters spell out everything else. You're not going to have 26 seconds between pressure rise and first drops and then get 40g in the cup in 15 seconds, but you could very well have 26 seconds to pressure rise with 1 second between first drops and full pressure and get a 15 second shot. I think the negative numbers will be interesting to examine, because then you begin to see how different amounts of PI influence the remainder of the shot. How does a shot with 4 seconds of dwell after PI compare to one with 15? Likewise, how does an additional soak of 4 seconds compare to longer soaks?

All of this ties back to what I believe Slayer was trying to accomplish polish with their pre-brew, which is to match the flow rate (water debit) to the natural wicking action of the puck such that the headspace fills around the same time the puck is saturated. This magical rate varies based on dose, headspace, grind and likely tamp (as I bet a loose tamp more readily accepts drops of water falling on it than a polished and nutated tamp, but that's just conjecture on my part...), but if you set a fixed flow rate you can then set a grind that gives you what you're after. My modified Rancilio S20 and Bianca both allow you to adjust the rate in real time so that brew pressure and puck saturation can occur pretty much whenever you want, within reason. This lets you look at other "recipies" and see what happens without too much guess work.

Maybe I'm making a molehill out of a mountain?


- Jake