Confused by the change in brew pressure during extraction - Page 2

Beginner and pro baristas share tips and tricks.
JModdd

#11: Post by JModdd »

Armanius wrote:Thank you. I increased the dose from 18g to 19g using the same beans, and the pressure kicked up to 10 and then dropped to about 8. Got about 29.5g yield in 30s total time. Shot came out acceptable.

How long do you wait until you start your first shot after turning BDB on? The lights indicate ready fairly fast.
When the indicator light comes on after its cold, I will touch the PF to make sure it's hot, but it usually isn't and needs to be brought up to the same temp as the group head. So I'll run brew water through the PF until it is hot. Should be good to go after that.

If I were you, I'd slightly increase grind size. With that darker roast stuff you're using, you definitely don't need it to brew for 30 sec. I'd stay somewhere around 20-25.

Hope this helps!

pcrussell50

#12: Post by pcrussell50 »

Armanius and I exchanged some PMs about this and I had him do some tests to rule out mechanical trouble in the Italian Ulka pump his machine uses:

1) it was able to pump 10 bar into a blind disc indefinitely.
2) it delivers 6.7 ml/s in open free flow.

Both are within spec...Except...

The pressure test does not tell the whole story. Once you drive ten bar into the group, it will tend to hold ten bar if the seals are fresh and good, until you release the pressure through the solenoid. So it's possible that the pump is unable to hold pressure. I have not experienced it with my BDB and I've been rocking a rotary for the last two years as well. But every so often here at HB and on other coffee forums you get threads (based on other machines than the BDB), dealing with various failure modes of the Italian Ulka pump that the BDB and so many other prosumer machines use.

The way to spot this kind of failure would be to rig up a "puck simulator"... a valve screwed into the bottom of the portafilter adjusted so as to allow say nine bar of pressure AND a leak down of about 1.5ml/s which is about the typical flow rate for a shot. If you're mechanically handy this would be pretty easy. If not...

...Or...

A new pump is not much money on Amazon and pretty easy to change (as long as you don't take advice on how to do it from DaveB ;)

And of course if it's still on warranty, it's worth a chat with Breville.

At this point, I cannot rule out the pump.

-Peter
LMWDP #553

Armanius

#13: Post by Armanius » replying to pcrussell50 »

I used a fresh bag of beans roasted three days ago, and same thing happened. Pressure went up to 8.5 bars after pre-infusion concluded, but then dropped to 5.5 bars for the remainder of the shot. In spite of the loss of pressure, I still got a 1-2 ratio of 18.5g dose with 37.5 yield with a 30s extraction, including preinfusion. Temp set to 201F and Breville grinder set at 7.

DamianWarS

#14: Post by DamianWarS » replying to Armanius »

Pressure is relative based on the resistance that the puck provides. If you want higher resistance grind finer or dose higher however what is more important is how the shot tastes and if you like it then don't worry about the pressure. The puck will naturally break down as the shot progresses and without something that restricts the flow there is not much you can do with that.

If you find on your grinder going down a step is too fine then you can try other tricks like putting a cut out paper filter to fit inside the PF (at the bottom of the basket). Your grind will have a bunch of fines in it and during the shot they will migrate to the bottom and clog the PF holes slowing the shot so a paper filter will prevent this from happening and it can allow you to grind finer, extract more and you probably will dose lower to compensate for the time change and higher extraction. You may notice that you get higher pressures too. Even without the grind change this is something you can try to see how it affects the shot as it can generally prevent channeling which may also increase the resistance of the puck thus you will see higher bars.

Armanius

#15: Post by Armanius » replying to DamianWarS »

The weird thing is that the flow of espresso coming out is nice and steady, and I actually still got a 1-2 yield in a 30s extraction. In the past, if I went too coarse, it would show low pressure, and I would end up with a 1-4 yield.

pcrussell50

#16: Post by pcrussell50 »

I thought Armanius was having a situation in which pressure was dropping AND flow almost stopped at the same time. THAT would be indicative of a stealth equipment failure.

Otherwise the rest of the discussion is good standard barista talk.

-Peter
LMWDP #553

DamianWarS

#17: Post by DamianWarS »

Armanius wrote:The weird thing is that the flow of espresso coming out is nice and steady, and I actually still got a 1-2 yield in a 30s extraction. In the past, if I went too coarse, it would show low pressure, and I would end up with a 1-4 yield.
Nothing wrong with 5.5 bars especially if the result is good. The pressure gauge can't be turned up by a knob or push a button to change it. Pressure is from the pump but in practice it's based on the coffee you put into it so if you want to increase pressure grind finer or increase the dose. This will probably make the shot longer (and increase the pressure) so you might want to consider other things to lower the time, like if you grind finer maybe you want to use 1gr less of coffee to keep the time.

To me, however the most important things in order is the dose, yeild, then time. If you put 18 in then stop at 36 out (or whatever ratio you choose) and aim for a time window that's acceptable to you. But it's more important to be strict on the yeild than the time. Dial it in and change dose/grind of course to get the time in the right window but I wouldn't stop a shot early because it went past a set time.

You got 18.5 gr of coffee with 37.5 gr output at 30 seconds. Does it taste good? If so no one cares what pressure it was at and if you can reproduce this then you've dialed it in successfully. You can still play with if you think you can go further but I wouldn't worry about the pressure.

Armanius

#18: Post by Armanius »

pcrussell50 wrote:I thought Armanius was having a situation in which pressure was dropping AND flow almost stopped at the same time. THAT would be indicative of a stealth equipment failure.

Otherwise the rest of the discussion is good standard barista talk.

-Peter
Peter, I have also had that happen twice, where the flow was slow after pressure dropped. Which makes things even more weird.

pcrussell50

#19: Post by pcrussell50 » replying to Armanius »

Is your machine still under warranty? Otherwise a new pump is $30 and not hard to swap. Cheap diagnostic. These same Italian Ulka pumps widely used on other machines, and there are threads where people have talked of refreshing seals and such on the Italian Ulka pump. But they're so cheap to buy new that unless you take pride in fiddling, it's worth more just to replace.

The key here will be to find a circumstance where you can repeat it at will.

-Peter
LMWDP #553

Armanius

#20: Post by Armanius » replying to pcrussell50 »

I bought it in early April 2020, so it's under warranty. Although the thought of not having a machine for days if not weeks is not appealing.

Is this the pump that you are referring to?

https://www.amazon.com/dp/B077ZRP3GD/re ... .Eb0VD4XWS

I made the grind finer by one setting, kept the dosage at 18.5g, and there was not as much of a pressure drop. It went up to 9 and then hovered at 7.5-8.