Breville Dual Boiler: Inconsistent espresso shots

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sorenwrang

#1: Post by sorenwrang »

Hi,

For some time, I have experienced a large variation in how my espresso shots flow on my Breville Dual Boiler.
As an example, I have made two espressos today (a few hours apart) using exactly 20.0 grams, in the basket, of ground coffee (same bean ofc). The first shot was 40 grams in the cup in 25 seconds, whereas the second shot was 33 grams in the cup in 28 seconds.
For both shots the coffee was carefully prepared with WDT, levelling and the same tamping pressure.

I experience this variation both on shots made with hours apart, but also between first and second shot made minutes apart.

What could the cause for such an extreme variation be?

My grinder is a Niche Zero.

Best regards,
Soren

vickeryj

#2: Post by vickeryj »

What does the pressure gauge look like while you are pulling the shots?

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sorenwrang (original poster)

#3: Post by sorenwrang (original poster) » replying to vickeryj »

Since the flow rate is so different, the pressure gauge reading is also different between the two shots. For the faster flowing shot the pressure is lower. In my opinion the pressure gauge just confirms the variation - it is not the cause.

FYI, I use a bottomless portafilter, and there are no signs of significant channeling, but I can obviously see the difference in the flow rate.

JRising

#4: Post by JRising »

And the third was very similar to the second, right?

Perhaps a little bit of stale coffee in the grinder chute overnight goosing your first shot.

sorenwrang (original poster)

#5: Post by sorenwrang (original poster) » replying to JRising »

The third is not always similar to the second. To be honest it is quite random.

Can 0.5 grams of stale coffee really make the difference between 40 g out in 25 secs and 33 grams out in 28 secs?

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Jake_G
Team HB

#6: Post by Jake_G »

Are you weighing the dose going into the grinder, or the weight of ground coffee in the portafilter?

sorenwrang (original poster)

#7: Post by sorenwrang (original poster) » replying to Jake_G »

It is the weight of coffee in the portafilter - so retention in the grinder is out of the picture.

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Jake_G
Team HB

#8: Post by Jake_G »

Well that's not helpful :lol:

To rule out exchange as a contributor, you can grind a really small amount of coffee, like 2 or 3 grams prior to your first shot.

If the issue remains, we continue scratching our heads. If the issue goes away, then there is definitely some coffee left over from the prior day's last session that is contributing to the issue.

Cheers!

- Jake

vickeryj

#9: Post by vickeryj »

On my bdb the pressure gauge builds up to a low level during preinfusion then jumps to its max pressure and stays there for a while, then starts to decrease as the puck loses integrity.

If yours isn't reaching the same max level between shots and holding it, that indicates that either your puck isn't providing enough resistance (which could be due to grind variance as others have said), or there is something wrong with the machine.

PeetsFan

#10: Post by PeetsFan »

Try pulling some dummy shots using the cleaning disc wrapped in plastic wrap (no cleaner of course). Take several. Does the pressure gauge show consistent results each time?