Using water debit to adjust espresso brewing parameters - Page 2

Beginner and pro baristas share tips and tricks.
pcrussell50

Postby pcrussell50 » Feb 10, 2019, 2:30 am

lancealot wrote:Bear with me, I am trying to get my mind around this.

Could water debit be considered a way to set or adjust maximum flow, in the same way that setting your OPV would set or adjust maximum pressure?


Yes. But those of us who extract through a "fast needle"* can adjust on the fly as the shot progresses from beginning to end. I think this is what Jake is talking about as the "third dimension" of a new, three-dimensional extraction-planning map. Such a "map" is of great interest to me, as the owner of a machine with this capability.

*Fast needle: a made up term that refers to a needle like the one in the Bianca, or the stock one on the BDB, or the "Jake valve" (which I have in my BDB), where you can vary the water debit from zero to max, within an anatomically reasonable arc, say 90-210 degrees, depending on the needle.

This is as distinct from say a Slayer, whose needle is of a slower or more "micrometric" nature. So rather than continuously variable flow throughout the shot, like Bianca, BDB, Jake,-valve, you can only switch between low and high, where the low debit is fixed at wherever you pre-set the needle.

-Peter

Moderator note:
Follow up conversation on flow profiling split to Controlling extraction flow to improve flavor
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lancealot

Postby lancealot » Feb 10, 2019, 7:38 pm

pcrussell50 wrote:Something that you could easily rig your BDB to do, BTW.-Peter

:wink: yes yes, I have been keeping track of the mod thread. I am asking these questions because I am trying to get my mind around what all this tinkering does before I make the move. One of the things that I have been finding challenging lately is that there does not seem to be any kind of guide for what happens to extraction with all these profiling options we have now. When I started out, I had the extraction diagrams to guide me - the ones that Jake included in the first post in this thread. I haven't seen anything like that for profiling. Am i correct to assume they do not exist yet?

pcrussell50

Postby pcrussell50 » Feb 10, 2019, 8:00 pm

No, the guide you seek does not exist. It is the "third dimension" to dose and grind that are already well known. This is new territory we are treading. And much needs to be learned. But I'm quite sure people are hard at work on it. In the meantime we can at least lean on what we have learned from the Slayer crowd and put that to use, even if it's not as full spectrum.

-Peter
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Jake_G
Team HB

Postby Jake_G » Feb 10, 2019, 8:01 pm

I'm trying to develop them now, starting with water debit, which is a fancy term for "how quickly you saturate the puck". I'm doing some tests to try and identify what quick start shots give you that slow start shots don't and vice versa.

One hypothesis is that high water debit (like LMLM or rotary La Spaz, etc...) gives you more body. We know that low water debit (take Slayer as the defacto example) gives you the ability to grind super fine and get higher extractions without having to dose super low.

The questions are really around what is in the space between these two extremes, if it can be tasted, and if so, if it can be used in the same manner as the charts posted at the beginning of this topic to adjust the brewing parameters of your shot. It may be that water debit is a second order parameter at best. You dial in your grind to get the extraction where you want it, dial in your dose to get the strength/intensity where you want it, but you find that the perfect combo of dose and grind doesn't quite seem to exist for you.

You grind finer to get a little more sweetness, but then you drop the dose off (so you don't choke the shot) and the shot loses the punchy edge that you really enjoy.

What to do?

I think this is where having the ability to recognize that decreasing your water debit a bit will allow you to use the grind that you prefer along side the dose that you prefer will give you an edge on dialing in your shots. It helps you find the sweet spot, and I believe makes the sweet spot much, much larger. Slow soaking of the puck makes the shot flow faster, and faster soaks make the shot pour slower. Knowing this, you can make that final tweak by trying a few different flow rates to start your shot and not have to chase your tail with the give and take of grind/dose that we normally encounter when dialing in a new coffee.

I'm still working on what the flavor impacts are on their own. For the record, I think they are small. But it's the enlarged sweet spot between grind and dose that makes this conversation worthwhile.

Cheers!

- Jake

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lancealot

Postby lancealot » Feb 10, 2019, 9:54 pm

pcrussell50 wrote:No, the guide you seek does not exist.


Story of my life!

These are exciting times for sure. I am grateful for the energy and thought you guys are putting into this. Thank you. :D

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Jake_G
Team HB

Postby Jake_G » Feb 11, 2019, 3:02 pm

nuketopia wrote:No worries, all in good humor.

I agree with almost everything you wrote. :lol:

"Water debit" is just an odd term to express volume flow rate with no basket present. Ie, zero-pressure maximum flow.

The terminology is bizarre, but it matches gicleur, as debit is French for flow and gicleur is French for jet... While water debit is simply a flow rate measurement (thanks for posting how to measure it for others! ), it is also a useful number because it helps define the relationship between the flow through the machine and the pressure drop between the pump outlet and the shower screen. When you measure it, the pressure drop is pump outlet pressure. This relationship defines the flow coefficient (Cv) of the entire system, which is the factor that determines what the difference between pump pressure and brew pressure will be on different machines at different flow rates.

Case in point:

A double shot pulled on any machine will have a higher average flow rate and a lower average pressure at the puck than a single shot pulled on the same machine. It's the puck that controls the flow rate between a single and a double, but the Cv of the machine determines what the pressure drop between the pump and the puck will be at that flow.

The zero pressure flow rate (aka debit) can probably be compared between machines of similar designs. But of very different hydraulic design, not so much.
...
Very hard to compare the two. I doubt one "water debit" value is applicable across different machine designs.

My S20 is also prodigious in it's water supply, but that is in factory trim without any jet at all. I first put a 0.5mm jet into the threaded 8mm hole and that calmed things right down. The needle valve I selected allows me to emulate up to a 1.75mm jet on the upper end. With my pump and hydraulic circuit, this gets me into LMLM territory. Regardless of complicated plumbing schemes or any other tricks under the hood, measuring the water debit (if it's fixed) defines the relationship of pressure and flow of the machine. It would be a farce to suggest that just by knowing the gicleur size one could predict with any accuracy what the brew pressure would be at various flow rates, but the water debit doesn't lie... I see no reason why debit by itself won't paint the complete picture of puck saturation and resulting back pressure the puck generates (based on the permeability of the puck, see last paragraph...) so long as one knows the pressure at the pump when the debit is measured. The only other (massive) variable is the puck itself and the headspace of your machine/basket combination.

It all gets into the dynamics of fluid flow and pressure through an annulus and a particle bed, which is a bit hard to sort out.

The pressure ramp of a puck of coffee is determined first and foremost by the puck itself (grind, height and surface area), and then by the combination of headspace volume and the water debit. The initial fill is easy, as it is just your water debit flow rate times the number of seconds it takes to fill the headspace sufficiently to start building pressure. Empirical testing suggests that 25 - 30ml is a typical volume that needs to be dispensed before drops start forming on a 58mm group with ~2mm headspace and an 18g dose. So we have the total volume pretty well figured out. How fast you dispense that volume determines how fast the pressure rises, and how much of that total volume the puck absorbs before building back pressure. I agree with your assessment that the difference between 0.6mm and 0.8mm jets would be small-ish.

Slow fill rates tend to stay steady longer and the pressure ramps up slower. Take a 2ml/s debit: Unimpeded by the puck, it would take 14s to deliver 28mls and saturate the puck and give you beads on the bottom of the basket. Instead though, the puck does impede the flow, and the pressure starts rising slowly and the flow rate starts slowly falling. The puck generates the pressure because water is flowing through it, and in response, the flow into and through the puck starts dropping. You dont see this drop in DE1 flow charts, because the pumps just pump harder to maintain the target flow rate, but it's present in all conventional machines. But in the real world (because apparently DE1s aren't "real" :P ), you get 2ml/s for about 5 to 8 seconds and then, depending on the grind, the flow rate then drops off to around 0.5ml/s over the next 10 to 15 seconds as the pressure rises, at which point drips form. Lower debits can take 30 or more seconds to saturate the puck and may not even build pressure at all if your grind isn't fine enough.

Faster flowing fill rates get through this process quicker, but experience the same basic dynamics. There is an initial fill where only the headspace is filled and the rate is steady prior to pressure building. Then the puck starts generating back pressure and the flow rate decreases. The same volume of water gets absorbed by the puck, but the spike in pressure happens faster, there is more dwell time between pressure being generated and flow beginning, and the resulting shot pours slower...

This last statement is really the crux of using water debit as a tool to adjust brewing parameters, as the rate at which water is introduced to the puck (water debit) has a very strong influence on the permeability of the puck once the pour begins. By making subtle adjustments to your water debit, you can control how fast the shot pours and then alter your grind or dose in ways that your machine would otherwise not be able to support.

Once again, this post is far too long and annoyingly over-technical.

Cheers!

- Jake

pcrussell50

Postby pcrussell50 » Feb 11, 2019, 3:25 pm

Jake_G wrote:It may be that water debit is a second order parameter at best...snip...

I'm still working on what the flavor impacts are on their own. For the record, I think they are small. But it's the enlarged sweet spot between grind and dose that makes this conversation worthwhile.

- Jake


Devastating :( ;)

All kidding aside, whatever we are able to learn from this is gravy. The more the better.

Lately while living in smug superiority that we can do more than just the two discrete steps that Slayer is limited to, I have begun to wonder if maybe their binary, low or high-only capability is really where most of the benefits lie? And that our super duper fancy pants, full control is, well, only second order as you are suggesting as a possibility.

-Peter
LMWDP #553

Zanderfy

Postby Zanderfy » Feb 11, 2019, 5:30 pm

Jake_G wrote:The pressure ramp of a puck of coffee is determined first and foremost by the puck itself (grind, height and surface area), and then by the combination of headspace volume and the water debit.
- Jake

Your posts may be technical, but they add tremendous value to the conversation. :) In your opinion, what variable(s) would you adjust first to address a shot that chokes? This happens often for shots on my Slayer (18g in an 18g VST basket, prebrew water debit is 55g/30sec) where the pressure gauge is already approaching 10 bar when the first drips of espresso start in the prebrew phase. Judging from what I've read in other Slayer fora, the headspace to water debit relationship may be more important than "grinding as fine as possible."

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Jake_G
Team HB

Postby Jake_G » Feb 11, 2019, 7:21 pm

Alex,

Were it my machine, I would be inclined to lower the debit to 45g in 30s. This should delay the peak in pressure by a few seconds (~18% longer than it takes now) as well as soften the puck a bit more. If pre-brew is taking an obstinately long time to give you drips, it's probably time to loosen up the grind a touch, but you can also drop the dose if you really need the high extraction that the fine grind gives you, and you're not getting decent flow after 30 seconds or so of pre-brew.

Cheers!

- Jake

pcrussell50

Postby pcrussell50 » replying to Jake_G » Feb 12, 2019, 5:18 pm

+1 here

In fact, it was the Slayer community that put that 1.5g/s debit into my head to begin with. And now, that or even occasionally as low as 1.0g/s is how I start a pull with lighter roasts. My thanks to the Slayer community for the work they've done pioneering this low debit-at-the-start, space and showing us what we can expect with this capability.

-Peter
LMWDP #553