Having trouble with Cafelat Robot - Page 3

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Starguru (original poster)
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#21: Post by Starguru (original poster) »

I just tried some dark roast at 145um. I think that was on the edge of how fine I can grind. I couldn't get a drop with pre infusion, and even at 8 bar the coffee came out in a trickle. I could not get the pressure gauge higher even with all my strength and weight, but from previous comments 8 bar should be more than enough with these burrs.

I was in a rush so didn't set up my camera, but it was off center. Still it tasted....good. Right in the middle, not sour, not bitter. It was probably my best shot yet.

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Jeff
Team HB
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#22: Post by Jeff »

Glad it is testing better!

There's a force/pressure graph in the manual that suggests around 55 lb-f for 9 bar. Page 23 of http://www.cafelat.com/uploads/1/5/3/6/ ... manual.pdf

jpender
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#23: Post by jpender »

It's worth mentioning that there's more than one way to push/pull those levers, depending on the height of machine (and you). It's quite possible to apply plenty of force without excessive strain. And still see the pressure gauge, if that's important to you.

Lots of people seem to push from above which makes it difficult to impossible to see the gauge. In videos Paul Pratt squats and pulls down, using some bodyweight, while facing the machine so the gauge is right in front of him. I stand to one side, push down with one arm and pull with the other, leaning over to the side. It's maybe a tad awkward but I can see the scale display, the pressure gauge, the espresso emerging from the bottom of the basket, and even get my nose right in there and smell it as it pours.

Be creative.

Ken5
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#24: Post by Ken5 »

Starguru wrote:I just tried some dark roast at 145um. I think that was on the edge of how fine I can grind. I couldn't get a drop with pre infusion, and even at 8 bar the coffee came out in a trickle. I could not get the pressure gauge higher even with all my strength and weight, but from previous comments 8 bar should be more than enough with these burrs.

I was in a rush so didn't set up my camera, but it was off center. Still it tasted....good. Right in the middle, not sour, not bitter. It was probably my best shot yet.
Sounds to me that you should grind coarser than you just did. Let us know how long it took to get that shot, it will help determine for sure if the grind was too fine.

If the stream out of the basket was off center I would think that has more to do with the robot not being level. When cleaning the basket you will see just how little of a tilt will cause a full basket of water to go off center.

Starguru (original poster)
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Joined: 7 months ago

#25: Post by Starguru (original poster) replying to Ken5 »

Yeah it took a while. The coffee came out in a trickle. Easily more than a minute.

I think the rubber ring on the bottom came off and the Robot wasn't level. Was surprised the shot tasted ok.

Jonk
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Joined: 4 years ago

#26: Post by Jonk »

Next time, if you notice that you can't get any beading during pre-infusion, back off slowly on the levers and try again with very little force. Usually that can save a shot from running slow. On the other hand, a minute is also fine for ristretto (you don't need to aim for the same output).

The beauty of the Robot is that it's so easy to adapt. Sometimes I'd aim for a 1:3 and notice that I need to try for 1:5 by slamming the levers. Sometimes it's like described above. The start of the shot is critical and you get good feedback so that you can react instantly.

Could be that the Zerno's pre-breaker and I guess also the V2 geometry means that you need a coarser setting. I'd often be in the 60-140µm range depending on roast level (but mounted horizontally in a Mazzer..)

Starguru (original poster)
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Joined: 7 months ago

#27: Post by Starguru (original poster) replying to Jonk »

I did try to back off slightly and reapply pressure but nothing came out until about 6 bar.


Can you expand on your "slamming the levers" example? What would you feel that lead to that?

Also, what is critical about the start of the shot?

Jonk
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Joined: 4 years ago

#28: Post by Jonk »

Try this:

Grind 2 samples at a bit coarser setting.

Then pull one shot without pre-infusion. Just 'slam' the levers to a high pressure right away.
The second shot, let the puck pre-infuse at very low pressure until you get droplets from every hole of the basket before applying 6-8 bars or whatever you're able to reach.

The first puck should meet with a lot more resistance. The second might not even allow you to hold the desired pressure. If you understand this, you can exploit it to get more acceptable shots by quickly adjusting the pressure profile to how the puck reacts. For example you can actually reach semi-high pressures with say a 30g dose of pre-ground supermarket coffee if you apply immediate pressure. It won't hold, but if you'd do it again with just the weight of the levers that might be enough to push all the water out at near 0 bar.

The puck is compressible and the more it's compressed the more resistance you'll get.

Ljkelly
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Joined: 7 months ago

#29: Post by Ljkelly »

When you talk about a vortex at the end of your shot, do you mean a cone of frothy coffee? If so, I'm guessing your beans are too fresh. That would account for the sourness, as carbon dioxide tastes sour. This would explain the both bitter and sour flavors you're tasting.

Starguru (original poster)
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#30: Post by Starguru (original poster) replying to Ljkelly »

Oh very interesting. I did not mean a frothy vortex, more like what I imagine channeling looks like. I've never seen it on my bambino.

My beans are about 3.5 weeks off roast at this point. When I started with the robot they were 2 weeks off roast.