Creeping Shot Variability Over One Hour

Beginner and pro baristas share tips and tricks for making espresso.
Kafana Nick

#1: Post by Kafana Nick »

Hello All,

I have noticed an interesting phenomenon as I make my morning shots. With a given weight of coffee in the grinder (18 g) and a set grind, from the first morning shot until the last (usually about 5), my shots progressively take a shorter time to reach 36 g. It is as dependable as a Swiss watch. To compensate, I alter my tamping, which I know is a bad idea and should be constant as well.

I barely tamp my first shot, and it comes out near perfect, 18 g in, 36 g out, taking about 33 seconds. By the last shot of the morning, I am putting my back into my tamping and am lucky to achieve the above output by 29 seconds, many times even less.

I let my machine warm up for at least half an hour before I start, so I can't imagine it is any kind of thermal issue. I keep everything else quite constant, using my scale for every shot. What gives?

Any ideas or suggested solutions would be greatly appreciated.

Thank you.

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Jeff
Team HB

#2: Post by Jeff »

If your tamp adjusts for a major change in shot time, I'd say one place to look is at your prep. Tamp really should never be used to adjust extraction.

18 g +/- a couple tenths, or always indicating 18.0 g, so +/- 0.05g?

Do you purge or vacuum your grinder every morning (or the like)?

A half hour for an E61 is barely enough. My experience is 40 min for reasonable thermal equilibrium.

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cafeIKE
Supporter ❤

#3: Post by cafeIKE »

+1 for min 45 minutes warm-up on e61.

tamp pressure, assuming consistent and level mechanics, has next to zero effect.

Are you weighing your shot in the basket after grinding to ensure ±0.1g?

Is the grinder close to the machine and heating up?
Can't comment on a Sette, but big shop grinders required constant adjustment through out the day for temperature and humidity changes.

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happycat

#4: Post by happycat »

Kafana Nick wrote:Hello All,

I have noticed an interesting phenomenon as I make my morning shots. With a given weight of coffee in the grinder (18 g) and a set grind, from the first morning shot until the last (usually about 5), my shots progressively take a shorter time to reach 36 g. It is as dependable as a Swiss watch. To compensate, I alter my tamping, which I know is a bad idea and should be constant as well.

I barely tamp my first shot, and it comes out near perfect, 18 g in, 36 g out, taking about 33 seconds. By the last shot of the morning, I am putting my back into my tamping and am lucky to achieve the above output by 29 seconds, many times even less.

I let my machine warm up for at least half an hour before I start, so I can't imagine it is any kind of thermal issue. I keep everything else quite constant, using my scale for every shot. What gives?

Any ideas or suggested solutions would be greatly appreciated.

Thank you.
Sette has a known issue of wandering grind adjustment due to three factors:

1. the felt ring inside the fine adjust wears down and there is less friction to maintain setting
2. the plastic gearset can wear leading to chatter and vibration
3. vibration can loosen screw securing gearset, and cause variation in microadjust ring

It's visible if you watch / use a phone to video the grind adjustment rings during the entire grind over multiple sessions. The grind setting can travel both ways... coarser and finer.

A symptom is noiser grind than originally, and somewhat random changes in grind.
LMWDP #603

Kafana Nick (original poster)

#5: Post by Kafana Nick (original poster) »

Hi Happycat,

I had that very issue with my Sette. They sent me a new grinder assembly, and I installed the 3 shims. It has stuck me as now staying right where I put it, but I will double check. In addition, I have not touched the adjustment rings for quite some time as I have found the best setting that is not terribly fine for my first shot and not terribly course for my last. It is compromise, and I know I could do much better if it weren't a moving target each morning. But if the grind adjustment were wandering, it would not be "resetting" itself each morning. This is a cyclic pattern.

Thank you!

Kafana Nick (original poster)

#6: Post by Kafana Nick (original poster) »

Hello Jeff and cafeIKE,

My earlier response to you did not post for some reason, so I will try again.

I preload my shots into mini mason jars, with each containing 18 +/- .05 grams. I have not been weighing my shots after grinding because of my knowledge of the low retention of the Sette, my earlier experiments to double check this by weighing before and after, and the long time I allow it to grind (an arbitrarily chosen 15 seconds).

I have been quite neglectful of my Sette 270 as of late. I will give it a good cleaning to see if that makes a difference. Were it a retention issue, I would expect it to be cumulative, and not reset itself for each new morning.

It is approximately six inches from my machine. I have never noticed it getting warm, but I can certainly move it further away. Is there a prudent minimum distance?

The half hour warmup I mention is the bare minimum; most often it ends up being an hour before I get started. And the creep in shot time/volume occurs regardless of the warmup time. It is extremely regular. And it is not over the course of a day, but rather over the course of less than one hour. I have not touched the grind setting in weeks, finding its current setting to be a compromise between "as course as possible" for the beginning of my cycle and "as fine as possible" for the end of my cycle.

It is frustrating to try to hit such a moving target, and the process resets and repeats itself every morning.

Thank you.

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Jeff
Team HB

#7: Post by Jeff »

Kafana Nick wrote:[...] the creep in shot time/volume occurs regardless of the warmup time. It is extremely regular. And it is not over the course of a day, but rather over the course of less than one hour.
My gut feeling is that it grinder-related. My first guess, without knowing your routine, would be stale grinds from the previous session in your first shot.

Giving a good cleaning seems like a good idea.