Controlling extraction flow to improve flavor

Beginner and pro baristas share tips and tricks.
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lancealot

Postby lancealot » Feb 10, 2019, 12:23 pm

So, I think I am finally getting this. In reading this and some other places. I think I have understood that one thing you can do with a needle valve that controls flow (like in the BDB mod), is control the flow of water at the end of the shot so that the flow through the puck remains constant or slows as the shot progresses. In my shots, if I let them run long, especially past blonding, it looks like the stream picks up and more fluid comes out in that part of the shot than in the beginning. Are we saying that this is useful because I can prevent this by restricting the flow with the needle? Is this the same as holding back the rise of a spring lever as it nears the end of the shot? I don't know anything about that other than reading that people like their levers because they can "slow the flow and save a shot" if they get the grind wrong.

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Split from Using water debit to adjust espresso brewing parameters

Mesmer

Postby Mesmer » Feb 10, 2019, 3:56 pm

For sure flow influences extraction a lot. For levers as far as i understand the flow decreases towards the end.

Regarding my initial query, it sounds like it would be easy to measure extraction flow in tank fed machines: just stick two flow meters on the tank, one for pump line and one for OPV return and then display the difference. Extra bonus for controlling the pump in order to keep a preset flow.

pcrussell50

Postby pcrussell50 » Feb 10, 2019, 4:14 pm

Mesmer wrote:For sure flow influences extraction a lot. For levers as far as i understand the flow decreases towards the end.


In spring levers, yes. As the puck erodes, the spring is decompressing and reducing the force applied to the piston. In manual levers, your arm is the source of force on the piston. As you see and feel the lever soften, you pull more lightly in response. (I have two manual levers). In needle valve machine, you have your eyes, your scale, and your puck pressure gauge as your guide to when and how much to close the needle. (I have one of these, too).

-Peter
LMWDP #553

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lancealot

Postby lancealot » Feb 10, 2019, 5:34 pm

With a spring lever, does flow decrease or does pressure decrease?

pcrussell50

Postby pcrussell50 » replying to lancealot » Feb 10, 2019, 7:12 pm

You've just got to go asking good questions, don't you? ;)

So here's what happens with a spring lever:
-You start the extraction by pulling down the lever, compressing the spring
-As the shot progresses, the spring un-compresses and exerts less and less downward pressure on the piston
-This ^^^ coincides with solids eroding out of the puck as the shot progresses, which would normally increase flow... IF pressure on the piston remains constant. BUT on a spring lever, the pressure on the piston doesn't remain the same. It decreases as the shot progresses. This has the "effect" of keeping the flow constant, because as the puck erodes, it takes less and less pressure to keep the same flow. I used quotes on "effect" because the declining pressure on a spring lever may or may not exactly match the rate of puck erosion.

On a spring lever, you have no control of the rate of declining pressure, except by swapping springs. In racing cars and downhill mountain bikes, spring swapping is part of tuning. I don't know if the makers of spring levers make a variety of springs to "tune" with.

But this is a thread about using water debit to adjust brew parameters, which implies the ability to set any water debit you want, on the fly. (Something that you could easily rig your BDB to do, BTW).

-Peter
LMWDP #553

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Jake_G
Team HB

Postby Jake_G » Feb 10, 2019, 9:26 pm

lancealot wrote:In my shots, if I let them run long, especially past blonding, it looks like the stream picks up and more fluid comes out in that part of the shot than in the beginning. Are we saying that this is useful because I can prevent this by restricting the flow with the needle?

Yes.

However I start my shots, I very rarely just let them run their course any longer. I generally gravitate to a 1 to 1.5g/s "flow" rate as measured by my scale as the shot is progressing. The first 10-15g in the cup are unrestricted (needle valve at some arbitrary "large" opening) and then I taper the valve position to keep the flow steady, as one would ease up on a manual lever or hold back the rise of a spring lever.

The results are nearly universally better. Less ashy notes, more sweetness, more separation of flavors. It doesn't seem to matter if it is a dark roast or a light roast, they just suit my palette better when the flow is held more steady. It would be an interesting candidate for blind taste testing to pull shots side by side, identical in every way except the declining profile.

Cheers!

- Jake

Bluenoser

Postby Bluenoser » Feb 10, 2019, 10:32 pm

On a vibe pump (assume rotary too, but only have vibe), you can put the lever to the neutral position for the last 4 grams.. Some say that helps the flavour.. Similar reasoning as above. I do it as a regular part of my shots, but haven't done an A/B comparison yet.