Bosco group: double vs single spring version [video]

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naked-portafilter
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Postby naked-portafilter » Dec 08, 2017, 5:12 am

There's been lot of debates about this topic earlier and it is an interesting one for sure. A bad news for those who expect now a DEFINITIVE answer: I can't deliver that.

We did some brewing with different piston gaskets some days ago. I made a few :-) shots (30-35) in quick succession.

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It was bit of a challenge changing the gaskets as fast as possible (releasing steam, pulling out a piping hot piston unit) but a huge beer jar came handy for cooling the piston unit and making the gasket change easier.

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Water inlets (still under pressure)

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It was interesting but the differences in yields and the observed pressure profiles showed only subtle differences. Except of this the original gaskets of the Pro800 weren't new which means it wouldn't be fair to reveal more about that.

The next day two friends came by with another Pro800. We removed the inner spring of the group of the machine in the roastery. A perfect setup for a comparison of two otherwise identical machines side by side (same pid setting of course). That's the video we made of the simultaneously pulled doubles:



As said, same grind/dose - 18,5g, temperature - pid 120C, same tamping force but the machine on the left without the inner spring, on the right with a double spring piston unit. As result different pressure profile (of course) peaks at 7 respectively 9 bar, different taste (no surprise), but same yield (45g), same pour (55 sec 10 sec pre infusion included).

It was interesting tastewise too. We pulled Ethiopean Jimma Seca and another farm selected coffee from El Salvador (both of them medium roasted) and a 100% arabica, dark roasted Belarbar blend (from a fellow roaster, Benvenuto Belardi in Umbria/Italy). All three of us preferred the dark roast with the single spring version but we were divided with the medium roasts. Making the results even more confusing I preferred the Ethiopean with the single spring setup and the coffee from El Salvador pulled with the dual spring group. I think there is no black and white in this debate but it was fun to make and very interesting to see the different pressure profiles BUT identical pours and same yields as result.

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TomC
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Postby TomC » Dec 08, 2017, 11:18 am

Nice work! I pulled the second spring out of my LSM group long ago and never looked back.

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Postby Javier » Dec 08, 2017, 1:00 pm

Hi Gábor! Amazing post, particularly your findings. I love every time you post a coffee-related video and/or coffee-related experiments.
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JohnB.
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Postby JohnB. » Dec 08, 2017, 1:17 pm

If the Pro 800 single spring peaks at 7 bar you might want to try substituting the spring used by Bosco which peaks just over 8 bar. It should hit a happy medium between the 2 set ups you tried & it works great with medium roasts.
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naked-portafilter
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Postby naked-portafilter » Dec 08, 2017, 1:38 pm

It was interesting also playing with different boiler pressures = different passive pre infusion intensity

As expected at higher boiler pressure (10 secs pre infusion time) the puck is more saturated which means the lever catches at earlier position (we have more water). The spring starts working earlier with more tension/force. See my measures below (dual spring version!):


A)
pid setting 115C - at about 0,7 bar boiler pressure

peak pressure piston 8,7 bar
shot volume 29-36g

B)

pid setting 120C 1,0-1,1 bar

peak pressure 9,5-9,7 bar
shot volume 43-49g

C)

pid 125 C, 1,5 bar

peak pressure 10,3-10,7
shot volume 50-56g

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redbone
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Postby redbone » Dec 08, 2017, 2:08 pm

Off Topic, Gabor I just noticed you changed names from "homo-barista" to naked-portafilter.

I could only imagine why you have done this. No more addendum needed at the end of your messages regarding name for starters,
ON A QUEST FOR BETTER ESPRESSO


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naked-portafilter
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Postby naked-portafilter » Dec 08, 2017, 2:21 pm

:-) we've been running some banners on hb which means we are "sponsor" and Dan made this name-change for me.

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Chert
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Postby Chert » Dec 08, 2017, 2:31 pm

redbone wrote:Off Topic, Gabor I just noticed you changed names from "homo-barista" to naked-portafilter.

I could only imagine why you have done this. No more addendum needed at the end of your messages regarding name for starters,


And the avatar is holding a port-a-filter and a tamper. Such accurate avatar-ism. :D

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Whale
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Postby Whale » Dec 08, 2017, 3:46 pm

Javier wrote:Hi Gábor! Amazing post, particularly your findings. I love every time you post a coffee-related video and/or coffee-related experiments.

+1

Slightly off topic, what is the "LED Tamper"?
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naked-portafilter
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Postby naked-portafilter » Dec 08, 2017, 4:44 pm

Whale wrote:Slightly off topic, what is the "LED Tamper"?


It's from a German espresso enthusiast, Markus. Tamper in action at 1:30


 
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