Help understanding Slayer flow profiling

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bostonbuzz

#1: Post by bostonbuzz »

So slayer has 9 bar running all the time. They have 2 pipes feeding, one at 9 bar, and one variably restricted via a needle valve, but also at 9 bar. I think they have two so they can quickly switch between them with the paddle rather than have 1 that does both (less complex to have 2?).

You could do this with a rotary pump dial and a brew pressure gauge, or a needle valve in the brew path and a marking where you get 60mls/minute (like this guy http://baristafail.com/?p=8) - am I right?

I'm missing something, otherwise flow profiling and pressure profiling are two ways of talking about the same thing... (except for the speed of simply filling the chamber with water at 0 bar ((once it's full it's simply slowly raising in pressure))).
LMWDP #353

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another_jim
Team HB

#2: Post by another_jim »

They are the same process with a different controlled variable. Pressure profiling means following a preset pressure graph throughout the shot by controlling either the flow rate or pump power; flow profiling means having a constant flow by controlling either the pressure or the pump power. Prefontaine advocates using the Slayer's controls to maintain constant flow.
Jim Schulman

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jonr

#3: Post by jonr »

Controlling flow makes sense to me - it effects how long the water is in contact with the coffee. Other than its effect on flow, does pressure actually make any difference?

Note that the constant 9 bars on the Slayer refers to before the restricting valve - the pressure at the coffee is reduced.

My guess is that it would be an unlikely coincidence if constant flow, constant pressure or constant temperature were optimal for coffee that is changing throughout the brew. The limited data I have supports this (ie, both temperature and pressure profiling are beneficial).

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bostonbuzz (original poster)

#4: Post by bostonbuzz (original poster) »

Thanks Jim. The main difference that I can tell is that with the restricted flow at 9 bar (x ml/minute) allows the coffee to restrict the flow and therefore determine its own preinfusion pressure (if the puck wasn't absorbing water at all, it would hit 9 bar soon, and be no different from zero preinfusion - at the other extreme, if it was super coarse, the water would flow through at ~1 bar at the predetermined flow rate). Based on the grind/bean characteristics, it will restrict the flow more and be at a higher preinfusion pressure, whereas a bean that restricts the flow less will be at a lower infusion pressure, given the same flow. The coffee can do what it wants to an extent.

This is different from preinfusing at a set pressure, because the latter doesn't change with the grind/coffee.

Correct?
LMWDP #353

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another_jim
Team HB

#5: Post by another_jim »

I would like to add another point. Profiling pressure requires programming a PID to control motorspeed or a bleed valve throughout the shot. This is not a trivial thing, as people with experience in prototypes and now the La Marzoccos that do this know. Flow profiling is much simpler. You can do it manually with a lever machine or any sort of manual control of a needle or bypass valve.

Having done flow control for several years now; I can pretty much guarantee that its drawing out of the extraction and preventing gushing do create more consistently good shots. You can easily make fully extracted ristretto (aka high brew ratio) shots shots, which are a lot trickier to manage on a conventional pump machine. It remains to be seen if the more involved pressure profiling machines can do more than this.

One area where the high tech pressure profiling may be better is in shops. Flow profiling is hands on, whereas pressure profiling is automatic. If it achieves the same benefits as flow profiling, i.e. more consistent and error correcting extractions; and allows "full auto" operation, so the barista can get on to the next order, it may be worth the extra cost.
Jim Schulman

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shadowfax

#6: Post by shadowfax »

bostonbuzz wrote:I'm missing something, otherwise flow profiling and pressure profiling are two ways of talking about the same thing... (except for the speed of simply filling the chamber with water at 0 bar ((once it's full it's simply slowly raising in pressure))).
John, I referenced your post on this new topic a few moments ago. I started out responding in this thread, but realized that my discussion extended broadly beyond the scope of this exact topic. That said, I wanted to place a marker here to reference this off-shoot in discussion-a preemptive thread split, if you will.
Nicholas Lundgaard