Hey guys, a couple of years ago, about 6 months before EricS developed his adaptor for the E61 temperature probe, and after reading Jim S's adventure with putting a thermocouple through the group head screw, i installed a thermocouple in my hex screw.
Mine, unlike Eric's is installed through a hole in the 6mm screw in the group, and soldered in place with silver solder. I used a tiny 1/16" stainless sheathed K-type TC from Omega. Smallest one they had.

It works great...but i'm not writing to boast:) I'm wondering if anyone can explain what i think i'm seeing.

For whatever reason i decided to start looking into my brew temperatures again, and trying to figure out how closely my TC shows brew temp. I did this after reading a lot of posts and data logging on Eric's adaptor, and how the brew temp is about 3-6 deg. lower than what the adapter shows.

That's where my question comes in. My TC seems to show basically the exact brew temperature., without any offset. I flush to 201, let sit for about 20 seconds, then pull a shot. The TC shows right at 201, without much variation. The only way i've been able to confirm this is with a small TC wire over the lip of the PF, onto the top of the coffee bed (this is why i just recently posted about renting a Scace..i'd like to do some testing with it). Both TCs read within about 1 degree of each other. Wow! That's great!

What i'm wondering is why would Eric's adaptor show an offset to the brew temp, and mine doesn't. Conceptually they are identical. I even took mine out and measured where in the water path the tip of my TC is (Eric explained where it should be for his adaptor), and mine happens to be placed almost exactly where he recommends placing his.

What do you guys think? Any ideas or thoughts?

Which machine do you have?

Oh yeah, sorry. It's an Isomac Tea.

another_jim wrote:Are you sure Eric's has an offset once the shot is underway? Are you sure yours doesn;t as the shot starts? It makes sense for the temp be initially higher in the group than in the basket, and then for the two to even out.

I'm asking if this simply could be a difference in the temperature logging gear (you might see initial offsets when looking at the readout of a dual channel recorder, otherwise not).

PS I remember your adapter -- way too much skill required compared to Eric's

What' i've read is that using Eric's adaptor the temperature about 20 seconds into the shot tends towards the true brew temp.
I'm not data logging on mine, but when i start the pump, within about 4-5 seconds, as the first drips start coming out, the temp is at 201, and stays that way, descending about 1 deg. through the length of the shot.

This same temperature profile/temperature is seen on the "over the basket" TC. I have a 2 channel TC reader, so i can look at the 2 values side by side.

PS: if Eric's had been available when i made mine, I would have used his with the nice swagelok system that allows the TC to be moved, retightened etc.etc.

The over the lip TC will give a good general indicator, but your TC is sitting atop a bed of cold coffee which will throw the temp off. Without having a reliable baseline it is hard to guess at what is going on. The Scace would verify the water temperature and you could compare that to your group bolt mounted probe. There tends to be several degrees delta between the group mount and the Scace for the first 15 or so seconds. As the shot progresses the temperatures slowly align until what you see at the end of shot is very close to the actual water temperature. There is nothing magic about the Isomac's, had a millennium for several years and it behaved the same. You could be very lucky, or you could simply be seeing the same offset between the two TC's because of how they are mounted. A calibrated Scace and meter would reveal that secrete.

Dave, that's why i was asking about a rental..i'll find out eventually if the rental fee is reasonable.

Having said that, the temperature on my readout does not drop almost at all for the whole shot (about 1 deg.), which is what i would expect if it were to approach a Scace reading. That's what started my wonderment.

My guess is a combination of factors :

Bolt is steel, not stainless
TC is brazed to the bolt
TC is .062, not .125
Over the lip TC is probably contacting the shower screen

This image shows the temperatures of .125 grounded T-TC in Eric's adapter and a bare K-TC mid-height in the puck for a 20s and 30s shot. The delta between the group and the puck will vary depending on the group TC insertion depth and the position of the puck TC in the cake.

Jason -

I would agree with the factors that Ian presented with the sole exception of thermocouple size. I do understand that response times between these sizes differ but the data I have show that those differences are minimal. Below is a graph of an extended flush and subsequent shot on an Isomac Ritual which, I believe, is fairly similar to the Tea.


I do remember the expression I used in a much older post and that was that the heat transfer antics within the grouphead of "our" espresso machines is quite complex. Of interest would be the temperatures you see under long term idle conditions and the response of the thermocouple during say, a 30 second flush only.

My group idles at about 212-213 on the TC. I can probably take a video tomorrow a shot..it'll show everything at once.
I'll take the video starting from idle, flush, wait, pull.