Brew temp too high

[simonp]

I've had a suspician for a week or so that my brew temp was too high, but having had problems with my thermocouple to multimeter module I have been unable to check it. The espresso i the cup has just seemed too hot, and the espresso flat.
Last night I borrowed the dedicated thermocouple meter from work, and measured the temp of the water in the portafilter spout, it was 103C
I opened up the Silvia to find that the sticky pad holding the bead thermocouple (for the PID controller) on to the side of the boiler was coming off. No problem thinks I, I have plenty of spare pads. CanI get one to stick on the boiler, can I b****cks These things are specifically for attaching thermocouples and are good for 250C, but as soon as the boiler heats up they come unstuck
I tried roughing up the side of the boiler with a scourer and cleaning with solvent but to no avail
I think my only option is a big jubilee clip, but finding one that size (about 80mm) locally could be tricky.
At the moment I have the thermocouple wedged in on the top of the boiler, but the espresso is much better, crema is much finer, and more dense too .

[phil]

Mmmm Simon you're either living at the bottom of a very very deep chasm where the air pressure is incredibly high, or maybe your TC is a little off? Or perhaps you're brewing with saline? 103 deg C? Nahhh

Anyway good to hear you've identified and are fixing a problem. I bet your espresso is sweeter and less bitter too.

[simonp]

Ooops, that should have been 100.3C not 100C

The irony of this problem is that about 3 weeks ago I had the lid off to take the pictures for the PID article, I checked the sticky pad then and it was in place fine!

[phil]

Ah yes the PID article.

[simonp]

Hmm, I've managed to get a pad to stick finally, and I've stuck a second thermcouple on top of the boiler next to the old thermostat. I am measuring a 15F (must get round to changing the PID to Celcius) difference between the top and middle-side thermocouples.
Now I am using a proper thermocouple meter I decided to re-check what PID setpoint gave me the correct brew temp.
I checked the thermocouple in boilng water whcih was about 99.5C so about right. With the PID set to 228F (my previous setpoint) I was still getting close to boiling water measured in a cut down polystyrene cup. The top boiler temp was over 240F. I dialled the PID set point down to give 232F at the top of the boiler (216F on the PID) which is the temp most PIDed Silvias seem to use (with top mounted thermocouples), and lo and behold, 93-94C in the polystyrene cup.

It looks like my previous cup mesurements were wrong, and I have been brewing my espresso too hot.
I have run a couple of shots with the new PID temperature, and they were certainly sweet tasting, but wheras before the espresso was way too hot to drink initially, I now find that it must be drunk immediately as the first part of the crema becomes cool almost immediately.

I read somewhere (can't remember where now) that you read a hotter brew temp when there is no coffee in the portafilter, and hence no pressure, does anyone have expeience of this? I had the thermocouple in the basket (running over the lip of the basket. I have the original Rancilio basket which is next to useless, so I may try drilling this to accept the thermocouple wires through the bottom so I can get the thermocouple bead in to the top of the coffe puck (as recommended by David Schomer) to see the real brew temp.

[simonp]

I managed to get a thermocouple into a filter basket and stuck in the top of the coffee puck. I ran a shot and monitored the temperature:
Initial temp as the first of the water hit the puck was 202F, which almost immediately dropped to 200F, after a second or two. Over a 25 second shot, the temperature never fell below 198.5F, which backs up the Silvia's reputation for steady brew temperature through the shot.
These temps were with the PID setpoint at 218F which is 10 degrees lower than I have previously been running, but this appears to give close to the correct brew temperature. Interestingly the temp measured from the top of the boiler with the PID set to 218F is 230-234F, which is around where most PIDed Silvias run with the PID thermocouple on the top.

One thing having these 2 thermocouples installed has confirmed is that the lower one on the side of the boiler does indeed suffer from fewer rapid fluctuations, and so, I believe, give a better indication of the conditions of the mass of water. Also the temperature measured by the lower thermocouple is much closer to the temperature of the water hitting the coffe during brewing, so this must also be a good thing.

With these lower temperatures I measured the temperature of the espresso in the cup after pulling the shot. First thing is how quickly the temperature falls, even with a pre-heated cup, I guess I should get something better than the cheap Ikea cups we have The temperature in the cup is around 160-170F which I believe is about right.
I certainly need a coarser gring now, and the crema seems thicker and more dense, and has a much more creamy mouthefeel. The espresso taste is also richer and sweeter.

I think the main lesson I have learned with all this is to check your temperature measurement equipment is correct before using it, boiling water being a nice easy calibration check.

[matts]

FWIW I just have my tc stuck under one of the screws on top with a bit of thermal goo, and have my PID set to between 225 and 228F usually. No idea what this produces in the cup apart from good taste!

Cheers
Matt

[simonp]

I found mine took too long to settle to a steady temp with the thermocouple at the top, but your PID controller may be happier with this location, mine has no fuzzy logic, so is more tricky to set up. If yours tatses fine then that's all that really matters, its all a hell of a lot better that the standard thermostat

[matts]

Hi simon

My PID isn't stellar, no fuzzy, but after the initial fiddling with the settings I've just left it, it keeps up OK for my usage. I've also taken to heating my cups in the microwave, 30 secs with an oz of water in gets them *really* hot. Maybe I'll get the tc out of my BBQ roaster and check the grouphead temp, I do have a styrofoam cup in the cupboard which has been there for about a year full of good intentions

I did try some other tc locations when I installed it but the response was too slow, as you say this may well depend on your controller algorithm.
I couldn't agree more about the PID idea itself, can't imagine going back.
Cheers
Matt