Different Shot Pressure Readings

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#1: Post by HowardW »

Hello everyone! I was hoping you guys could help me. I have the Breville Dual Boiler and Sette 270. I think my technique is pretty good. I've come to a point where my shots are pretty consistent. Most of my shots are clean and flow well with no real mess with the naked portafilter. I'm using the stock basket and have been using 21 gram doses of Counter Culture Coffees with 41 to 50 grams out depending on the coffee. Lately I've been using Hologram and La Golondrina. Currently using a Ugandan from them. My technique is to grind into the plastic cup that came with the Sette. Then I pour that into the portafilter so that it mounds nicely. Then I use just a few, gentle palm taps to settle the grounds down. I then use an OCD knockoff and tamp. (This is from Lance Hedrick's videos.)

Here's my question. One time I will get a consistent pressure reading of 5 bar. Then anther shot will be 7 bar. And then sometimes 8 bar. With the blind basket the pressure reading is 9.5 to 10 bar. The flows are all nice and consistent but the pressure just varies shot to shot. And the pressure is pretty consistent. A 7 bar shot stays at seven bar. A 5 bar shot stays at 5 bar. And these are all with the same grind setting. (I do get the occasional shot where the pressure varies during a shot, which I take as obvious channeling. I sink those shots.) Does this mean there is channeling even if the shot itself is well behaved? Taste isn't too far off between the shots. I'm just trying to figure out what is going on.

Does anyone have any guidance on what could be happing and what I could do differently? I do have a WDT I made with a cork and acupuncture needles, but I find that the shots are more consistent without it. I have ordered the Decent funnel so I can experiment with more aggressive WDTing...

Thank you!

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Team HB

#2: Post by cannonfodder »

That is rather odd. Changes in the max brew pressure would be due to a higher flow rate and less backpressure. A 5 bar extraction from a machine that produces 9 bar would indicate massive channeling. I would expect it to be gushing water with the shot taking little more than a few seconds.

The other possibility is a faulty OPV valve so the pump bypass is dumping water before it gets to the puck. They are simple spring-loaded valves that open at a given pressure. If you take the return line out of the water reservoir and put it in something like a cup. Pull a shot check to see if it is dumping a lot of water out the return line. You will normally get a little but at 5 bar it would be pumping out lots of water.
Dave Stephens