# Brew Pressure (OPV) on MaraX



## Hellsent

I'm sure we've all seen James Hoffmans video about the MaraX, one of his bad points about it was how unhappy he was that the machine came with such high brew pressure from the factory as it touches 10bar or slightly more on the pressure gauge on the machine. Realistically at the group this will be less but still probably in between 9-10bar.

After looking at flow profiling and reading up about brew pressure for espresso I keep seeing more and more posts about lower pressure, even down to 6bar!!

Scientific paper here: https://www.cell.com/matter/pdfExtended/S2590-2385(19)30410-2

Blog post: https://strivefortone.com/2020/09/19/low-pressure-turbo-shots-and-the-perfect-espresso/

Insta post:

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http://instagr.am/p/CQsX5lHB1sg/

So, I'm definitely sold on changing my OPV valve to a lower brew pressure, but my question is, what do you have yours set to? Have you changed it at all? Was it difficult?

Thanks


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## Bicky

I'm thinking of doing the same. I assume you've watched this -


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## Hellsent

Bicky said:


> I'm thinking of doing the same. I assume you've watched this -


 Yes just watched that before posting this thread, was curious if anyone had any tips or tricks, how many counterclockwise turns they did? Or if anyone else has done some experimenting with super low pressure under 8 bar and not liked it? Just a bit apprehensive about opening it up for the first time


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## siliconslave

So i did this yesterday, was showing 11bar on the machine and turned it down to 9bar now (might turn it up a little when i've run some more coffees through.

Instead of removing the tube from the OPV i used a 12mm open jaw spanner and held onto the tube with my other hand, its a bit fiddly initially but you can get the spanner in from the right (as you face the machine) and hold on with your left hand. Once in position you can turn the opv bolt about 90degrees while stopping the tube twisting. I did about 180 then tested with the lid off, turned it off and did another 45 or so checked and repeated so probably about 360 in total.

Literally took me 10min including taking the lid off, checking, adjusting and replacing, took longer finding the tools and blind filter tbh


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## Bicky

siliconslave said:


> So i did this yesterday, was showing 11bar on the machine and turned it down to 9bar now (might turn it up a little when i've run some more coffees through.
> 
> Instead of removing the tube from the OPV i used a 12mm open jaw spanner and held onto the tube with my other hand, its a bit fiddly initially but you can get the spanner in from the right (as you face the machine) and hold on with your left hand. Once in position you can turn the opv bolt about 90degrees while stopping the tube twisting. I did about 180 then tested with the lid off, turned it off and did another 45 or so checked and repeated so probably about 360 in total.
> 
> Literally took me 10min including taking the lid off, checking, adjusting and replacing, took longer finding the tools and blind filter tbh


 I've also just done it there, 10 minute job. Never bothered removing the silicone tubing either, it didn't seem to be twisting or under any stress.

I was at just over 10 bar, dropped it down to about 9 for now. I was going to say it took about 1 full turn, but maybe it was less going by what @siliconslave has said. Probably best to do a half turn, check what effect that's had, then adjust from there 👍


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## siliconslave

After a bit more faffing with the grind I seem to be running at 9.5 on the usual 35seconds to 1:2 (20g:40g) so quite happy with that, seems to have improved the crema significantly.


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## Hellsent

siliconslave said:


> After a bit more faffing with the grind I seem to be running at 9.5 on the usual 35seconds to 1:2 (20g:40g) so quite happy with that, seems to have improved the crema significantly.


 Have you tried grinding coarser? With less pressure there should be less need to grind as fine as normally for espresso. Apart from crema can you notice any taste difference? I need to find a spanner and give it a go today


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## siliconslave

Hellsent said:


> Have you tried grinding coarser? With less pressure there should be less need to grind as fine as normally for espresso. Apart from crema can you notice any taste difference? I need to find a spanner and give it a go today


 Well stupidly I did it at the same time as starting a new bag so hard to tell how much of a flavour difference i'm getting, but i'd noticed i've been getting very thin and light crema for the last couple of months, despite getting reasonable flavour and ratios.

I'm defiantly grinding slightly coarser that previously though.


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## Hellsent

Bah! I've done it and am shaking my head wondering:
A) Why didn't I do this sooner
B) Why does it ship with such high pressure from the factory???

Struggled to find a 12mm spanner so used an adjustable one, turned out it was too big to fit in the machine, but found a smaller one in the end. Gave it a few good twists thinking this will take me down to the region of 9 bar. Screwed everything back on and turned it on and did a blind filter test and it had only taken off about 0.3 bar from the initial 10+.

A bit frustrated but opened it up again and gave it a few more turns. This time I didn't screw things back in until I tested it.

Down to just under 9bar with a blind filter so decided to screw everything back together.

Pulled a shot and my god 😁

Less bitterness/harsh flavours, probably caused by uneven extraction of the puck (even though I WDT and use a distribution tool)

"Softer" on the pallet, not sure if placebo but it felt softer, like @siliconslave mentioned, probably more crema.

The spent puck also came out of the basket completely intact compared to it being broken up (albeit slightly) every time before.


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## MediumRoastSteam

PS: Reducing pressure doesn't have a direct correlation to grinding coarser (and vice-versa). When I did this with the Pro-700 back in the day and more recent with the Elizabeth, I found the exact opposite happened.


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## siliconslave

Hellsent said:


> The spent puck also came out of the basket completely intact compared to it being broken up (albeit slightly) every time before.


 I'd love to have that side effect - still getting loads of coffee left over in the basket


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## Bicky

How are you guys getting on with this? I'm really pleased. I've not done any side by side comparisons with the original higher pressure, but I am getting some really tasty coffee, possibly more balanced than before.

From looking at the bottomless PF I'm definitely getting cleaner looking shots with less spritzing and a nice stream which comes together quickly, suggesting a more even extraction and less channelling? I think my shot times have been more consistent as well. Possibly the integrity of the puck holding up better under the lower pressure? I only went down to about 9 bar, I'm considering going further, 8 maybe.

Also as @MediumRoastSteam said, I'm not having to grind finer to achieve similar shot times, probably about the same. Grinding coarser seemed like the intuitive thing to do, so what's the explanation for that not being the case?


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## prezes

Decided to do it this morning and got it set at just under 9.5bar. As one of the previous comments there's more crema with every shot today.

funnily enough I swear I made one full turn initially which took it down to near 7.5 and felt like 2 full turns to take it back to 9.5bar


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## rxmnt

How does pressure affect the extraction and taste?


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## Hellsent

rxmnt said:


> How does pressure affect the extraction and taste?


 Apparently, higher pressure can cause more channeling and therefore more uneven extractions. As well as more inconsistencies due to the above.


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