I was wondering if there were any new flow rate scales out there. I know the Pearl S will display grams/seconds and at least one other of the Acaia scales will display flow in their app. But I'm curious if there are any other scales out there (perhaps cheaper ones) that'll do it was well, preferable display it like the pearl does. I'm not married to my phone, and most mornings would prefer to leave it off until after I've had my coffee.

I have a QM Carola on the way with flow control, and according to the website there is 5" cup clearance, so with a naked portafilter, I think even a thick scale should be OK, but preference would also be given to something smaller.

Edit: I decided to check out their apps, figured I could explore the brew guide and what not, And wow, for a pricy scale, their apps don't seem to work to well. Def makes me question spending the money, since the brew guide
For pour over and what not were part of how I was justifying a $200 scale to myself ha ha

Decent is just releasing their new scale. It's bluetooth and will be compatible with apps that should be able to calculate flow rate for you.

The Atomax Skale II is a proven design and manufacturer. Its protocol is open and sane. Its firmware can be field upgraded. It can be field calibrated with either a 500 g or 1000 g weight. Python code under GPLv3 is available, runs on macOS, Linux, and should on Windows as well. PM me for details.

Estimating flow from a scale is relatively easy, but has been done very wrong with apps in the past. There will always be some delay. The shorter the delay, the more noise in the estimate for a given scale resolution. When I wrote the replacement scale code for the DE1, I settled on a one-second window with an 0.1 g resolution scale. This works out to 1/2 second of lag and 0.1 g/s resolution.

Thankfully, espresso is generally slowly varying in its flow rate. A delay of 1/2 second for the estimation, 1/3 second for the internal lag of the scale electronics, another 1/10th or so for Bluetooth stack, what you're seeing is close to a second after the fact. It is definitely good enough for bulk measurements, like "the flow in the middle of high-pressure extraction is around 2.8 g/s" or "the flow at the end of high-pressure extraction dropped down to around 2.5 g/s". Anyone that thinks they can see channels opening and closing with scale data is likely deluding themselves, especially as the previous DE1 app code had around a two-second time constant introduced by its filtering (so nothing happening faster than around 1 second would be visible).

Several of the Acaia scales have been reported as having a subtle "stickiness" to them on around a 3-second period. It's not visible to the eye, but shows up as steps in the mass-flow estimate. A few of the people I worked with tried different settings on the scales but collectively were unable to determine if it was a specific mode, setting, or collection of them.

I see that the Acaia Pearl had been 'reimagined' in 2021. Seems there have been some improvements including a flow scale on the display. Personally I don't know anything about it.



From their website.

Curious to know how it is myself, and if Acaia will bring this to other models soon.

Ken

I agree that weight-based flow rate calculations aren't going to let you see what's happing in real-time. I think they might be somewhat useful for altering the rate of flow with a gear pump or needle valve after you get a feel for how the flow rate changes for a particular coffee and grind. For example, if you see the flow rate accelerate at around, say, 20 seconds, you can anticipate that when pulling the next shot and start to compensate by reducing the flow.

Note that the weight method can't be used to calculate the pre-infusion flow rate. Further, a weight-based flow rate for a shot won't be the same as the flow rate for an equivalent weight of water due to the difference in volume between a given weight of water and the same weight of coffee.

My modified GS/3 AV uses an Arduino to monitor the machine's flow meter. The Arduino flow rate display is pretty-much real-time, but the code sends the flow rate to an Android app running on a tablet or phone via Bluetooth, which does introduce a bit of delay, but I'd say it's no more than one second, and probably less. It's perfectly adequate for real-time flow control, even if I'm a second behind the actual flow rate. There's something of a timing pattern in the flow rate, so I can usually anticipate when it's going to speed up, and I start reducing the flow rate a little ahead of time. The app also monitors my Acaia Lunar scale via Bluetooth, and there the delays are more apparent. In fact, when using the option in the app to cut the shot at a particular weight, I have to set the weight one or two grams lighter than the target weight.

I can't say that even the fast flow rate display is useful for seeing channeling in real-time because the flow rate can increase because the entire puck has become more permeable, not necessarily some part of the puck. It's more useful to watch the bottom of the basket in a bottomless PF, where I can see any uneven flow as it happens. My Android app displays a chart showing pressure, flow rate and weight when the shot has completed, and that's where I can sometimes see evidence of channeling in the form of a brief drop in pressure and increase in flow rate.

Peppersass wrote:Note that the weight method can't be used to calculate the pre-infusion flow rate.

We might be using the same words to mean different things, so let me temporarily disagree with you there, and we can see if that's the case.

On the DE1, I absolutely use weight-based flow rate tracking to determine the optimal preinfusion flow rate.

How?

After preinfusion ends, and pressure rises, I look to see if "flow rate into the puck" = "flow rate out of the puck".

If preinfusion has been successful, then the two flow rates should match. The puck should be fully saturated.

If the preinfusion flow rate is too fast, then the flow rate out of the puck will be slower than the flow rate into the puck.

Why? Because there are still dry spots in the puck, absorbing some of the water. Preinfusion has not been fully successful, and you are making an espresso that is extracting unevenly. This is an extremely common flaw, likely endemic to flat-9-bar machines that have no preinfusion, but it's totally solvable on lever machines, or semi-autos with preinfusion control.

This "compare the in/out flow rate" approach has helped me find that *most* coffee pucks can absorb water at about 4.5 ml/s, though some max out at 3.5ml/s. I can tell the absorption rate by varying the flow rate, and seeing if the pressure on the puck increases. If it does, then we are feeding water at the puck faster than it can absorb.

-john

Thank you to all who have responded.

Based on responses, I think I should clarify, my goal is to attempt to keep grams per second consistent (I know using a scale like this, I'll always be chasing the mouse so to speak). More in an effort to save potential bad shots during dialing in, or when to start tapering off near the end of a shot. I'm coming from the world of lever machine (flair) and like that while dialing in, I can feel a grind is too coarse and ease up on the lever a bit, or as the puck erodes and resistance decrease I can lower the pressure.

So my thought was that even if it's only updating every .5 second, it would still give me an indication that flow is increasing earlier in the process than I would notice with my own eyes (I don't have confidence that my powers of perception are that fine in the mornings)

How I see this playing out,

I use the pressure gauge to gauge pre infusion, keeping it to about 2bars till first drops (15-20 seconds on my flair) then I gradually open the flow control over the next 5 seconds or so until I top out at 1.5g a second, then taper down as needed as the puck erodes trying to keep at that target of 1.5g a second.

I am however totally willing to accept that I may be way over thinking things.

decent_espresso wrote:After preinfusion ends, and pressure rises, I look to see if "flow rate into the puck" = "flow rate out of the puck".

Thanks for your comments, John. I'm not familiar with the architectural details of your machine, so forgive me if I'm missing something.

How do you determine the "flow rate into the puck"? You can't use the scale for that. Without a flow meter, I think the only way to do it is to know how much water it takes to saturate the puck and fill the basket. Then you can calculate the flow rate into the puck from that pre-determined preinfusion water volume and the time it takes for the pressure to start rising, right? If this is how you do it, then how do you know what the preinfusion water volume will be? It varies with dose, grind, basket size, etc.

Jeff wrote: Several of the Acaia scales have been reported as having a subtle "stickiness" to them on around a 3-second period. It's not visible to the eye, but shows up as steps in the mass-flow estimate. A few of the people I worked with tried different settings on the scales but collectively were unable to determine if it was a specific mode, setting, or collection of them.

Wonder if it affects all of them? A reason not to consider getting one?

Jesse.F wrote:
How I see this playing out,

I use the pressure gauge to gauge pre infusion, keeping it to about 2bars till first drops (15-20 seconds on my flair) then I gradually open the flow control over the next 5 seconds or so until I top out at 1.5g a second, then taper down as needed as the puck erodes trying to keep at that target of 1.5g a second.

I am however totally willing to accept that I may be way over thinking things.

I think it totally makes sense and I would aim to do something similar on the Robot. I think it would be more useful than pressure and time indicators, as that's exclusively what I look at on the DE1 to see how the shot is working out (as well as checking the bottom of the portafilter).

I think the limitations listed by others are probably not deal breakers for the use you're going for.

I should play around with it too and see what I learn. Haven't had the Robot out to play lately. I am getting the new Decent scale soon, and I do have the Skale2, but haven't ever looked for an app for that. (Oh, and what of these actually fit under the Robot... hmm... ).