Trying a much faster flow for my robot pull at the moment, had about three shots so far and have two observations.

First taste. My average preinfusion/pull with old grind setting was about 20/30. Last 3 shots averaged 9/22. Perhaps closer to the range suggested for normal machines as I see a lot of folks here recommend much longer times with their robots. Overall I liked the faster shots more. Different aftertaste,... better. Faster shots seem a little weaker, but will need time with new settings before going back to old to be able to notice the difference. Right now I am favoring the faster shot.

What do you guys usually strive for in your timings? Anyone go as low as about 10/22 as a goal?

Could it just be the coffee? I had coffees that no matter what I did they were always sour. Could it be that these coffees are the ones that do well with the very long timings?

Second observation I have I have noticed for a while and I am wondering if anyone else finds this too. A pull with a very fine grind takes a lot more pressure on the levers than a pull with a coarser grind to get the 'same reading' on the gauge. I would have thought that the force needed for the different grinds would be the same as long as the gauge achieved the same reading with the difference only being with flow and timing. The difference in energy needed is quite noticeable!

EDIT:

I put the scale on a bathroom scale as per jpender's recommendation and pulled shots at different grinds. Scale all registered same weight. Weird illusion of the mind as it feels much different!


Ken

Ken5 wrote:Second observation I have I have noticed for a while and I am wondering if anyone else finds this too. A pull with a very fine grind takes a lot more pressure on the levers than a pull with a coarser grind to get the 'same reading' on the gauge. I would have thought that the force needed for the same reading would be the same at the same gauge reading with the difference only being with flow and timing. The difference in energy needed is quite noticeable!

It has to be the same force. But your muscles don't measure force like the gauge does. Pushing against relatively static arms versus arms that are slowly dropping will feel different to you. Also a finer grind will simply take longer to pull through so your muscles will fatigue.

From a purely physics standpoint the energy is simply the gauge pressure * piston face area * mechanical advantage * arm travel distance. But the chemical energy your muscles burn through varies depending on the force and even occurs when pushing against an immovable object. A better mechanical advantage would make it all a lot easier but then it wouldn't be a Robot. It would have some other shape.

That is why I am confused about the force needed. The levers drop faster with the coarser grind perhaps giving the effect that less force is needed, and it is shorter.

But with the finer grind I am definitely pressing harder, not just longer. More energy, hands hurt, and the feeling that the robot is flexing a little front to back all only happens at finer grind. Even the wife makes a comment when watching me press at finer grinds!

Doesn't make sense which is why I asked. I will continue to pay attention to the different grinds to see if I come to a different conclusion.

Ken5 wrote:But with the finer grind I am definitely pressing harder, not just longer.

Put your Robot on a bathroom scale and you'll see that what you perceive as "harder" isn't more force.

I will put it on a scale and get back, probably not in the next few days as I am almost at the end of this bag of beans and like what I am getting at the moment.

If it is an illusion type of effect it is quite believable!

Ken5 wrote:Trying a much faster flow for my robot pull at the moment, had about three shots so far and have two observations.

First taste. My average preinfusion/pull with old grind setting was about 20/30. Last 3 shots averaged 9/22. Perhaps closer to the range suggested for normal machines as I see a lot of folks here recommend much longer times with their robots. Overall I liked the faster shots more. Different aftertaste,... better. Faster shots seem a little weaker, but will need time with new settings before going back to old to be able to notice the difference. Right now I am favoring the faster shot.

What do you guys usually strive for in your timings? Anyone go as low as about 10/22 as a goal?

Could it just be the coffee? I had coffees that no matter what I did they were always sour. Could it be that these coffees are the ones that do well with the very long timings?

When you say "pull" time, does it include the preinfusion time or not?

Anyway, I think short vs long shot time depends heavily on the coffee and own's taste preference. Keep in mind temperature drops rather fast on Robot. So when I hold long preinfusion, I'm also basically saying ok I'll be using low brew temp. In fact, quite low if you don't preheat the piston, according to data shared by jpender. Some coffees do ok to well at such low temp, some don't. And I don't think it's as simple as lighter vs darker roasts. I'm still experimenting heavily and learning new things daily. Lately, I've been incorporating basic piston preheating to my routines.

Times of both are listed above. My preinfusion is basically determined by my grind. I basically press at about 2 bars till the scale reads 0.3 grams. I guess due to my technique the faster the preinfusion, the faster the flow during the actual pull.

Ken5 wrote:Times of both are listed above.

Yes I see them in xx/yy format. Does yy include preinfusion or not was my question.

First value is only prefusion at 2 bars, second value is only pull at about 7 bars.

I see, thanks.
Then you might try going even faster! Like 22 sec total (maybe with 5 sec PI). That's what Gwilym Davies suggests in his dial-in guide for some coffees.

BTW, I think his guide is excellent. Simple, effective and easy to follow. Wish I had found it much earlier.