And I wasn't sure whether to post this topic under Modifications or Tips or some other section ... I finally decided to post it in this section since the point of it all is to get a really great shot consistently. (Please relocate if you think this fits somewhere else better)Since working with the Mini VII, I've been a bit frustrated trying to get a consistent temp ... especially since the whole reason I purchased this machine was because of its reputation for consistent shot temp. What I was finding was that in order to get the group up to temp (cold nose) requires a whole lot of flushing - more than the typical 2x2oz that I was reading most people here use. I was finding I needed to flush about 4x2oz or even 6x2oz to get the group up to where I'd get the same temp on the first shot that I would get on the second and third shot. (and I have read at least one post where a user was saying his first shot is never as good as 2nd and 3rd - and I think this is why).
As an experiment, I mounted a K-type thermocouple probe into the group head. I used a very quick reading probe that was right in the water flow above the group (inserted into the hole where the mechanical pre-infusion device goes). I ran like that for a week or two and learned what I could about how warming flushes correlated to brew temp. With the TC right in the water flow, it read much hotter than the group while the water was flowing fast (say flushing into a cup) but when the water flow stopped (flushing into a blind basket) or slowed way down (pulling a shot) the temp reading would drop to the temp of the group. (this is because the very hot water from boiler was moving slowly enough for the cooler brass mass of the group to pull the temp down)
The K-Type probe was only a temporary thing (wires dangling about) but I learned a lot. So then I took an inexpensive Taylor instant read - and pulled the wire and bead out of the metal sheath (so it can read quicker without the metal mass of the skewer) and attached the bead directly to the group and the readout mounted just above the control buttons.
I find that the group cools down to read about 83C within a couple of minutes of pulling a shot. Then it takes 2x2oz flushes to get back up to 86C or 4x2oz to get it back up to 88C or 6x2oz to get up to 90C.
If you were making espresso for a group and pulling back to back shots (and did the 2x2oz flush before the first), at the end of the first shot the group will be reading 87C, end of second shot 88, end of third = 89C, end of fourth = 90c, end of fifth - 91C, end of sixth and it's up to 92C and that's where it will stay for subsequent shots until you allow it to sit for a few minutes.
In my testing, if I just want to pull one shot ... I find I either have to pull 6-8x2oz flushes OR I can just set the temp up 2 degrees higher and do the standard 2x2oz flush. But then I'd have to remember to set the temp back down if I'm going to pull several shots.
I've found having the thermometer to be extremely handy for getting consistent shots. It has me thinking of how I could modify the group head with a PID controlled heater just for the group itself ... but that's for another project, right now I'm pretty happy with the results using the thermometer so I can get the group warmed to the same temp I know works.
- S1_Thermometer.jpg (130.04 KiB) Viewed 28056 times
- Group.jpg (63.51 KiB) Viewed 28056 times
It is so good to have someone like you on the forum that tingle with the mechanics to make it even better. A few years back I was more active, but I think I'll be copying this mod.