mixespresso wrote:One question that I have also asked myself is whether repeatability is sensitive to small differences in the time it takes to ramp up to 6 bars after finishing preinfusion.

It is. A slow ramp and a quick ramp will not pull or taste the same. So, at least fairly large differences will make a noticeable difference in my experience.

I think it's a better approach to use a scale and stop at the desired weight. A few seconds more or less won't have as much impact as several grams less or more in my experience. I think it's a lot easier to pull consistent shots with the Robot compared to the pump-driven machines I used to use because it's easy to make minor adjustments throughout the pull.

mixespresso wrote:Maybe this is the reason why some people recommend ending the shot by colour

I've never been able to figure out what is supposed to be the end of the shot by color. I stick to the ratio I've found works well, adjusting grind to make the flow not too slow, not too fast. When a particular shot runs faster/slower I still pull the ratio and most of the time the shot is good anyway. I had a shot this morning that ran for 50 seconds instead of the 30-32 seconds I was used to. It was tasty!

I've wondered about the dynamics of ratio versus contact time and I can't unwind it in my tiny brain.

My scale does not fit the robot and I have to admit that I have felt somehow "unconfident" without it. My new mini-scale is on the way

To remove variables in this learning phase, I have used the same coffee grains since I got the new burrs. Most of the time, I have used 17g doses. So far, I have not managed to pull good pre-infused shots with doses <17g

jpender wrote:I've never been able to figure out what is supposed to be the end of the shot by color. I stick to the ratio I've found works well, adjusting grind to make the flow not too slow, not too fast. When a particular shot runs faster/slower I still pull the ratio and most of the time the shot is good anyway. I had a shot this morning that ran for 50 seconds instead of the 30-32 seconds I was used to. It was tasty!

I've wondered about the dynamics of ratio versus contact time and I can't unwind it in my tiny brain.

Granted this is super, super subjective, but I recall that between shorter and longer shot times, I tended to taste less bitterness when I tended towards the shorter times.