How to maintain consistent flow rate throughout extraction?

Beginner and pro baristas share tips and tricks.

#1: Post by Hiruma »

Hello everyone,

I am hoping for some advice on what I should adjust to stop the flow rate from starting off slow and then increasingly significantly around 15-20 seconds into a double shot. I can try to get pictures later on if they might help. For reference, I just started learning about espresso!

My prep process before pulling a shot
I am using a Gaggia Classic Pro with medium roast beans (approx. 2-3 weeks after roasting) ground with a Sette 270 at settings that are quite fine (3-4). I changed the spring on the Gaggia to reduce brew pressure to 9 bars, warm the machine up for at least 20 minutes before using it, and follow temperature surfing guides to try to get the temperature as hot as possible (turning on the steam button before brewing). I dose directly into the bottomless portafilter with a funnel, use a 0.4 mm acupuncture needle for WDT, level with a Motta 58.4 mm distribution tool and then tamp with a 58.4 mm tamper calibrated to around 30 pounds.

The sad result
The first 5-6 seconds seem fine as I can see coffee slowly covering the bottom of the basket quite evenly. The flow begins and everything looks "right" (based on those neat extraction videos on youtube) until around 15-20 seconds where the stream turns into a grossly wide upside-down triangle that sometimes even contains bubbles. The flow at this rate is completely beige/blonde. The result this morning was 17g in, 34g out in 32 seconds and the taste was sour/astringent and overall unpleasant. I didn't see any holes or cracks in the puck afterwards.

What I have tried
I've tried grinder coarser, but that just makes the significant increase in flow start earlier. I've tried grinder finer as well, but that just delays the inevitable. I've tried skipping WDT since I thought I might be creating holes in the puck, but the result is channeling all over the place. Overall, it seems that no matter what I try, the espresso I pull always has some unpleasant acidity and the flow rate is almost never consistent.

If you have any pointers on what I should start adjusting to resolve this issue, please let me know! Thanks in advance for your time and advice!

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#2: Post by Peppersass »

It's normal for the flow rate to increase after peak pressure has been reached. Usually it starts off slowly, then gets faster and faster until it reaches a plateau, which can be pretty fast. This is caused by the puck becoming more and more permeable as water passes through the puck. And the faster the water flows, the more permeable the puck becomes. So the flow can get pretty fast pretty quick.

Generally speaking, it's not possible to get a "consistent" (did you mean "constant?") flow rate after peak pressure has been reached unless you have a lever machine or a pump machine with variable flow rate control (adjustable needle valve or gear pump.) However, you can and should keep the flow rate from getting too fast.

I would start with the grinder. Since you have a Niche Zero coming, you have the opportunity to determine whether the Sette 270 is capable of producing the grind you need. While I don't know if the Niche Zero will solve your problem, based on the reviews I've seen it's considered to be quite good, and I would expect an improvement if grind is the primary problem.

If you're not weighing the grounds with a scale that has 0.1g resolution, you should do so. Assuming you're using the Sette with a hopper, if the dose is sometimes smaller than it's supposed to be, which can occur when the level of beans in the hopper decreases, then you can get faster flow after peak preasure, or even a gusher. You shouldn't have that problem single dosing with the Niche Zero, but be sure to weigh the grounds, not just the unground beans. Retention can cause the two to not be equal (RDT can help with that.)

It's not surprising that not doing WDT makes things worse. Even top-notch grinders may require WDT, depending on the coffee and extraction parameters. It's also important to make sure that the coffee extends all the way to the edges of the basket before tamping, and that you get a good seal between the puck and basket when you tamp. And be sure your tamp is level.

Note that the situation gets worse if your machine allows you to slow the flow down with long, slow preinfusion. That makes the puck even more permeable (though this is offset by the grind being much, much finer.) Often it's necessary to gradually reduce the flow rate after max pressure has been reached in order to maintain a constant flow rate, and that requires a lever or a pump machine with variable flow control.

BTW, this wasn't as much of a problem in the old days, before light/medium roasts and longer shots became popular. Dark roasts tends to fracture when ground and produce more fines, which slow down the flow, and shots were often run shorter, either with the Italian Normale of 25 seconds or even shorter with Ristretto. As long as the puck was prepared properly, there wasn't enough time for the flow to get too fast.

Nowadays, with lighter roasts that fracture less and require longer pull times, you need a grinder that produces a consistent grind with reasonable ratios of particle sizes. You also need meticulous preparation. And you may need a machine with a gentle ramp to full pressure and consistent pressure thereafter. Alas, as you're finding out, capable grinders and machines usually cost more.

Hiruma (original poster)

#3: Post by Hiruma (original poster) »

Thank you very much, Peppersass, for the detailed feedback!

Yes, "constant" would be the correct word to use for my situation. I do weigh the ground beans after grinding as I find that the Sette 270 likes to keep at least 0.5g for itself when I put 17-18g through it. I will see how things turn out once the Niche Zero arrives in a month or so, and I do hope that it helps with my flow rate/unpleasant taste woes.

In the meantime, should I try to grind even finer while paying close attention to the weight inside the portafilter after grinding? I have never tried RDT but will be testing it tomorrow morning.
Alas, as you're finding out, capable grinders and machines usually cost more.
Very much so! The person who sold me the Gaggia at a local espresso shop pointed out all sorts of machines and grinders for thousands and thousands of dollars, telling me I would be back for these sooner or later. At the time I thought my GCP and 270 would be the end of it, but boy was I wrong.

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#4: Post by cafeIKE »

It goes about like this:
Coffee 50%
Grinder 25%
Machine 15%
You 5%

3 week old coffee can be marginal, especially if it sits in the hopper.
Who roasts the coffee?

A pal has a Sette and makes very good espresso. He just tamps moderately with no falderal. He is Italian, so...
The niche Zero is very, very good. I've used one for a couple years. There is no need to weigh the grounds with it.

Tamp pressure is largely irrelevant. 30# is less than 10% of the pressure the water applies to the puck . An even distribution and true and level tamp tops tamp pressure six ways to Sunday.

If you put the portafilter in the machine and then remove it without brewing, is there any mark in the coffee? If not, try adding ½g increments until the coffee just touches the screen, then use ½g less. Adjust grind for correct flow.

I've not tried a ditro tool like the Mottta. If doing WDT correctly, there should be no need.

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#5: Post by Jeff »

Grind and dose for flavor.

The guidelines are just that. The coffee doesn't have a stopwatch. Guidelines are helpful for getting in the ballpark, but from there, it's down to taste. Take notes of how things change when you change things. With a modest-priced setup, there will likely be variability from shot-to-shot that is out of your control. It may help to try a few shots with one set of parameters to confirm the changes.


#6: Post by Jesse.F »

Lance hendric (sp?) Just posted a video on how to get the most out of your machine. One thing to try might be to turn the stream wand on (into a cup) when you see the flow going up. This will reduce the flow to the puck. Assuming I understood his explication of how to do pre infusion with your machine.


#7: Post by spopinski »

For a true constant flow, you'll need a lever machine or pseudo lever like decent profile. However you can mod almost all pump driven machine with a needle valve.

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Hiruma (original poster)

#8: Post by Hiruma (original poster) »

Thank you cafeIKE, Jeff, Jesse.F for your input as well!

The beans I buy are roasted by local coffee shops/roasters in Vancouver, Canada. I dose 17g in my VST 18g basket because anything above leaves a mark in the center, which I assume means the coffee is pressing against the shower screen.
I've not tried a ditro tool like the Mottta. If doing WDT correctly, there should be no need.
I will try a few times with just thorough WDT and no distribution tool in the next few days. Thanks for this!
Guidelines are helpful for getting in the ballpark, but from there, it's down to taste.
This is very true and is something I need to continue working on. I visit different coffee shops in town every now and then to try to get a feel for different flavours and an "ideal espresso" for me to chase, but almost all the espresso bars serve sour espressos here in Vancouver. I guess I'll just have to get better at taking notes and working towards something I find delicious!
Lance hendric (sp?) Just posted a video on how to get the most out of your machine
Thanks for the info! I will google that and see what I might be able to incorporate into my routine.

Hiruma (original poster)

#9: Post by Hiruma (original poster) »

Thanks, spopinski!

I shall add that to the things for me to look up in the next while. Never heard of or thought about needle valves. Appreciate the tip!

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#10: Post by Peppersass »

Flow control (needle valves, gear pumps, etc.) is an advanced technique that's primarily useful for pulling difficult-to-extract light roasts. I wouldn't get into that until you can pull a good shot using traditional techniques. You should be able to do that with a medium or dark roast, consistent grinder, proper distribution and a consistent machine with a reasonable ramp to full pressure.

VST baskets are great for lighter roasts because the hole area is larger than most baskets, which forces you to grind finer, which in turn will extract more. But they usually require more care in preparation. You might try the stock basket that came with your machine or a different brand for comparison.