E61 Preinfusion

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

#1: Post by oksako »

Is this a thing?
  1. Lift the lever to ON position
  2. Wait until desired pressure for PI is reached
  3. Set the lever to mid-position, so that the pump gets disabled, but the extraction doesn't stop --> Pressurized preinfusion (kind of a blooming) is happening
  4. Lift the lever to continue extracting with target pressure until finished
Note: I'm not speaking about the "prewetting" without pressure, where you just lift the lever to mid-position without lifting it all the way up beforehand.

Nunas
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#2: Post by Nunas »

Yes, it's definitely a thing :D for machines not plumbed to the water mains and before the popularity of flow control device kits, many of us did this all the time. I have an FCD on my Synchronika, yet still do this often.

DeGaulle

#3: Post by DeGaulle » replying to Nunas »

I suppose you do need a group pressure gauge? If you have an FCD, obviously it's there, but if not... most E61 machines show the pressure at the pump outlet, but I expect that as the pump is building pressure, the pressure at the group lags behind due to the resistance of the gicleur.
Bert

Nunas
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#4: Post by Nunas »

A gauge isn't necessary, once you get used to your machine. On my Magister HX, I had an EricS thermometer, so couldn't fit a brew pressure gauge. With a bit of trial and error, I determined that about five seconds of pump was about right. You need to give it enough time for the water to displace the air in the puck and wet all the grinds, but not so long that coffee begins to flow. Usually, I'd wait until I saw the first few drops of coffee coming out before lifting the lever back to brew. If the coffee came out sooner than I wanted, I'd let the first gram exit (I always use a scale), then lift the lever. Of course, with a brew pressure gauge, the experimentation is greatly reduced, as one can see what's going on with the gauge.

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cannonfodder
Team HB

#5: Post by cannonfodder »

oksako wrote:Is this a thing?
  1. Lift the lever to ON position
  2. Wait until desired pressure for PI is reached
  3. Set the lever to mid-position, so that the pump gets disabled, but the extraction doesn't stop --> Pressurized preinfusion (kind of a blooming) is happening
  4. Lift the lever to continue extracting with target pressure until finished
Note: I'm not speaking about the "prewetting" without pressure, where you just lift the lever to mid-position without lifting it all the way up beforehand.
Ideally, you would need the machine plumbed into your water mains so you have around 3-4 bars of input pressure. Then you can lift the lever to mid-position which will open the solenoid and allow your mains pressure to fill the expansion chamber and start the pre-infustion/extraction. After you hit your desired preinfusion period which is usually when you get beads of coffee starting to show on the basket you can lift the lever the rest of the way to turn on the pump to do your full extraction.
Dave Stephens

bettysnephew

#6: Post by bettysnephew »

I discovered this hack on my unplumbed E61 VBM and it improved my espresso immensely. Just wait until the basket shows coffee on the bottom of the basket and then switch to pressure side of valve to extract your dose. Worked for me.
Suffering from EAS (Espresso Acquisition Syndrome)
LMWDP #586

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bluesman

#7: Post by bluesman »

DeGaulle wrote:I expect that as the pump is building pressure, the pressure at the group lags behind due to the resistance of the gicleur.
Pressure is force per square area, eg pounds per square foot or kg per square cm. It is equal throughout a contained fluid, which is the basic principle of hydraulic lifts, elevators, brakes etc. As long as the cross sectional area of the fluid path is large enough throughout to allow the needed volume to flow per unit of time (eg "2 ounces per second"), pressure will be the same everywhere in the system regardless of focal diameter. If there's an area too narrow to flow the required rate, it will cause lower pressure beyond the constriction. But a gicleur in a standard machine that passes enough water to make espresso is not that tight.

Flow control devices are variable constrictions, and when almost closed they do restrict flow enough to cause a pressure drop. But a typical gicleur will not.

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Jeff
Team HB

#8: Post by Jeff »

My experience with unplumbed E61-style machines is that piddling on the puck is about as unappetizing as it sounds. For me, it was far from repeatable and uneven to the point of encouraging channeling. Definitely better than just the HX pressure, but not repeatable enough for me.

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Jake_G
Team HB

#9: Post by Jake_G »

bluesman wrote:If there's an area too narrow to flow the required rate, it will cause lower pressure beyond the constriction. But a gicleur in a standard machine that passes enough water to make espresso is not that tight.
David,

I'm sorry, but this is not quite right.
There is always a pressure drop when there is any fluid flow through a system. In fact, without a pressure drop, the water has no reason to flow at all. This post in the ramble shows the relationship and the effect of gicleur size on how steeply pressure drops off, bases on the flow through the system. Point being that it is a continuum, and there is not a point where the gicleur "kicks in".

Cheers!

-Jake
LMWDP #704

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bluesman

#10: Post by bluesman »

Thanks, Jake. But I think Bernoulli would have agreed with me. The pressure within and immediately after the constriction is lower in inverse proportion to the velocity of the moving fluid (which, in this instance, behaves like a gas). But this is only to maintain flow. As soon as the conduit widens enough to cease being the flow limiter, the pressure rises again because the velocity drops. And the delta P that drives flow is not within the open system - it's at the ends.

In an open system like an espresso machine, I'm pretty sure the pressure at the puck is equal to the pressure at the inlet side of the gicleur as long as the gicleur isn't so tight that it reduces flow at normal pump pressure (in which case we call it a flow control device). I guess I should have qualified my original post statement with the proviso that pressure within a moving fluid column will vary with local velocity in accord with Bernoulli's equation. But as long as the flow rate at the outlet is unrestricted at working pressure, that pressure drop across the system (i.e between pump and "shower head" in the group) will remain constant. The force exerted by the water will change with the area of the outlet, but the pressure (ie the force per square area) will be the same at both ends minus only the slight differential required to force the water through the puck (which, as you point out, is why it flows at all).

It would be great if an HB participant turns out to be an hydraulics engineer and will weigh in :D

Best regards - D