Does flow control save a bad shot?

Beginner and pro baristas share tips and tricks for making espresso.
patrickneil

#1: Post by patrickneil »

I have a Lelit Bianca and use the flow control paddle quite a bit. I am wondering if what I'm doing isn

I start with 20g of coffee and I typically use the paddle to preinfuse for 2 seconds by fully opening for 2 seconds then closing. I keep the paddle closed for 5 more seconds. I open the paddle up at 7 seconds and more often than not I have the paddle at somewhere between 30-40% for 9 bars and then, as time goes on and pressure drops, I open the paddle more and more to hold 9 bars and eventually get to 90%-100%. When I'm at 20g I drop pressure down a bit and finish with 30g right around 35 seconds.

If I didn't have flow control, full pressure would likely be 12+ bars so I would say my grind is too fine. However, does the flow control make up for a bad grind? Or should I really be opening the paddle all of the way up to be sure my grind is correct? In short, does it make a difference or does the paddle save a bad shot?

PIXIllate
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#2: Post by PIXIllate »

You really need to start by mapping the flow rate (or water debit) from the group at various positions of the paddle. You should also set your OPV so that pressure never goes above 9 bar. At 10 bar the puck undergoes a secondary compression that is always a bad thing for coffee. Some people set it even lower to 7 or 8 bar.

Basically you set your paddle at the most closed position and put a cup on a scale and run the group for 20 seconds. Take the output in grams and divide that by 20 and you have your flow in ml/sec. This is the language used to describe preinfusion along with pressure. So if you got no water from the group your flow rate would be 0ml/sec.if you got 40g out in 20 seconds your flow rate would be 2ml/sec, if you get 160g out your flow rate would be 8ml.sec.....and so on. Once you map the flow for your *full open* and *full closed* positions map a few in between positions. Now you can build a repeatable flow profile.

What I do is start the shot at 7.5ml/sec for 3-4 seconds to quickly wet the puck and then move to the position that gives me 4ml/sec and watch the pressure gauge until it reaches 4 bar. This is the the maximum flow rate a puck can absorb water in its uncompressed state and the point at which the puck fully compresses and you are no longer *pre-infusing*. At this point open the paddle back up to the 7.5ml/sec position and let the streams come together and flow.

This approach will get the puck wet from top to bottom as quickly as possible for an even extraction while still allowing the puck some extra time to soften, heal dead spots and saturate before you apply full flow. As an added step you can also ramp down the flow toward the end of the shot as the puck begins to flow faster as a majority of the solids have been extracted.

Hope this helps. I've been meaning to shoot an updated video of this process as it's easier to do than it sounds.

patrickneil (original poster)

#3: Post by patrickneil (original poster) »

Thanks for that. Can you tell me the best way to set 100% at 9bars? Should I use the back flush basket and make sure it caps out 9 bars or is there a different way to do this? Then I will take the rest of the steps you recommend as well. Thanks so much!

PIXIllate
Supporter ♡

#4: Post by PIXIllate »

Yes, use the blind filter and set it to 9 bar.
Good luck.

patrickneil (original poster)

#5: Post by patrickneil (original poster) »

Thanks!

elkayem

#6: Post by elkayem »

PIXIllate wrote:... You should also set your OPV so that pressure never goes above 9 bar. At 10 bar the puck undergoes a secondary compression that is always a bad thing for coffee. ...
I have not heard the term "secondary compression" before and am curious, tell me more!

Also, my Bianca max pressure is set to 10 bar, and have never noticed any ill effects at this pressure. I usually try to dial in my grind to get the right flow at 9 bar, but if I'm a little off, I have found bumping up the pressure to 10 can help. If I left the pressure at 9, the shot can get overextracted and that definitely spoils the shot. So in my experience (with reference to the OP's question) flow control can definitely help to save the shot.

pham

#7: Post by pham »

I have not heard the term "secondary compression" before and am curious, tell me more!

The folks at Decent mapped out a rough relation from Darcy's law empirically that flow correlates with the square root of pressure when combining other factors such as puck height, solution viscosity, and bed permeability. At 10 bars, that correlation seems to stop working and flow is said to decrease at pressures above that, so they attributed it to the puck reaching a second compression state. So, first compression at 4 bar, "espresso flow" in between, and then second compression at 10 bar. In practice, I don't think there's rigorous proof that this happens because of puck compression effects, but it's a hypothesis. Sidenote, I honestly haven't seen this relation mapped out at various flow rates either. Perhaps different grind profiles will behave differently since some seem to flow much faster at higher pressures.

elkayem

#8: Post by elkayem »

pham wrote: The folks at Decent mapped out a rough relation from Darcy's law empirically that flow correlates with the square root of pressure when combining other factors such as puck height, solution viscosity, and bed permeability. At 10 bars, that correlation seems to stop working and flow is said to decrease at pressures above that, so they attributed it to the puck reaching a second compression state. So, first compression at 4 bar, "espresso flow" in between, and then second compression at 10 bar. In practice, I don't think there's rigorous proof that this happens because of puck compression effects, but it's a hypothesis. Sidenote, I honestly haven't seen this relation mapped out at various flow rates either. Perhaps different grind profiles will behave differently since some seem to flow much faster at higher pressures.
Interesting! Thank you for the explanation. I have not experienced a decrease in flow above 9 bar but will be on the lookout for it now. After preinfusion, I will slowly open the paddle until I reach 9 bar. If I'm not getting the flow rate I want at that point, I will continue to turn the paddle to a higher pressure. Flow always continues to rise for me when I do that.

PIXIllate
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#9: Post by PIXIllate »

I would still recommend setting the OPV to 9 bar and controlling the flow with grind setting and preinfusion. Higher pressure will not get you anything good.

Remember, the longer you preinfuse the faster the end of rhe shot will flow.

DamianWarS

#10: Post by DamianWarS »

patrickneil wrote:Thanks for that. Can you tell me the best way to set 100% at 9bars? Should I use the back flush basket and make sure it caps out 9 bars or is there a different way to do this? Then I will take the rest of the steps you recommend as well. Thanks so much!
Pressure should be calibrated to allow optimal flow. This is in the range of 9 bar but it depends on where the pressure is measured. As pressure ramps up the flow increases but to a certain point and with too much pressure it compresses the puck more and flow decreases.

If you run a shot with very close attention to details for exactly 30 seconds with the paddle fully open you can take an average of a group of shots in the same pressure range ignoring outliers to determine the flow of that pressure then increase/decrease until you find the pressure that yeilds the optimal flow. Start low and move up. Once you narrow the pressure with the fastest flow you can go to finer increments to be even more percise. If you need to make a large correction in grind size like new burrs or a new grinder then you will have to recalibrate.

In doing this it doesn't matter what the pressure reads 9 bar, 8 bar or higher/lower because you know the pressure is set to the optimal setting. There is a pressure gradient from pump to puck and unless you have a scace thermofilter this is the best way to set pressure if you have fine control over the pressure.