Spitz.me wrote:I used both a robot and a Flair 58. You have to increase your own pressure on the lever as the shot runs longer to maintain a pressure since resistance diminishes. The Robot isn't unique in this sense, in my experience, but some are reporting that it is enough so that it separates it from other levers.

I think I missed your gist the first time around - of course I don't think the Robot changes the pressure on its own.

This is my second bag of beans. The previous one was dark roasted, and it was easy to brew a good shot; I even got the impression that I could make a great shot with my eyes closed. Now, I bought a light roast, and it's more challenging hitting the sweet spot and avoiding a sour taste. I've mainly been trying to maintain the pressure in the range of 6-8 bars, and when it drops, I apply more force to keep it in that zone. I've never had experience with machines like the Robot, and I'm trying to identify patterns. For example, in what situations does it make sense to maintain pressure and when to let it decrease?

If you get sour, sounds like you'll need to preheat the Robot, particularly its piston, before you pull your shot. Look back over the past few days of posts in this topic where jpender provided a little info (including a link IIRC) to get you started. Lighter roasts are more finicky than dark, particularly with the Robot. But it can be done.

Thanks, I'll take a look at it. I always preheat the basket but not the piston.

Spitz.me wrote:I used both a robot and a Flair 58. You have to increase your own pressure on the lever as the shot runs longer to maintain a pressure since resistance diminishes. The Robot isn't unique in this sense, in my experience, but some are reporting that it is enough so that it separates it from other levers.

I think what you're missing is that the angle affects leverage. If you would attach weights to the lever(s) like in this video: ...you'd get different pressure profiles from a Flair 58 and a Cafelat Robot.

I'll admit that I don't fully understand the calculations, but I think this is what happens:

• Flair 58 starts out with very low leverage (call it natural pre-infusion ), increases and then maxes out by the end of the shot when the angle is near 90 degrees.. or starts to decline a little bit if you pull high ratio shots.
• Cafelat Robot starts out with a little more leverage, increases quicker - maxes out before a regular dose 1:2 ratio and starts to decline.

For a similar shot you're closer to 45 degrees with a Robot when you reach the end. Bad news if you wanted a straight 9 bar profile because it requires more and more force. On the other hand, if you wanted it to 'naturally' decline to a bit more than 6 bars that is pretty much what a constant weight/force would do.

Ratio, dose, fill etc. all comes into play - as well as more and more complicated* physics. Corrections are welcome.

*to me..

Light roasts need a workflow like this:

1. Maximize heat: preheat piston and basket (overfill method works well here).
2. Grind extremely fine. Aim for 1:2.5 or 3 ratio in *60 seconds*. Preheating the piston keeps the Robot temp stable over this time.
3. WDT. Enables you to grind finer than if you don't, and if you're getting any channeling at all the shot is going to be bad. Much less room for error here than with dark roast.
4. Start at 6 bar and decline to 4 by end of shot. This was heresy to me coming from the world of classic espresso, but it truly improves the shot in terms of balance of flavors.

(PS: place paper filters above and below puck).

The above is good advice. If you want an easier time, you can invest in a grinder better suited to those kinds of roast - for example a DF64gen2 with SSP MP burrs. In my experience you'll then have better success also with faster shot times. Even higher ratio can also be helpful - you can do up to 1:5 with the Robot, for a different but tasty style called allongé.

have you guys tested whether, for light roasts, the more the shot resembles a pour-over (longer brewing time & lower pressure), the more resulting balanced flavour ?

I followed the advice to heat the piston. Previously, I only heated the basket. The acidity in the light roast decreased. I used a stand with a glass of boiling water to warm up the piston. But it's a bit complicated, I want to simplify the process. I'm thinking of buying a stovetop steamer for this purpose. I will need it anyway for frothing milk. Something like a Bellman steamer.

Hi, some ideas for you:
1. Some like it hot threadfor heating up the robot piston (links to hb here)
2. Cafelat recently released a basket plug (links to cafelat uk store)
3. Breville's/Sage's 58mm silicon flush disk can used same way as #2, but you need to use a spare basket (e.g. pressurized basket)
4. "thundies" - message "churls" on instagram for these (links to instagram) -- search youtube for videos
5. If you have access to a 3D printer or a library that does 3D printing for you, you can find similar thing to "thundies" on the various model websites
6. etsy has similar offerings
7. some people pour boiling water from the top of the robot down into the piston and then turn it upside down during cleanup to get rid of it. If you watch the robot assembly videos here you can what's on the inside of the robot then decide if you want to do this or not.

Lots of options that are safer than holding up a glass of boiling water!

For steaming milk: I used to have a bellman steamer long, long ago and didn't like it much. It doesn't work well on gas stoves and gets friggin hot on the hands; the electric one is a lot easier to use, not sure it is made anymore. If you are willing to do the microwave dance, then using a small french press or an immersion blender will get you pretty good milk foam. In the "Some like it hot" thread above, there's a link to a stand-alon steamer. I think the "Meticulous" people are working on one, too. Or, you can purchase something like a breville/sage bambino specifically for steaming.