new controlled roaster

[JavaB]

Re: new controlled roaster

Thanks for that. the thermocouple Ive been using untill now was fibreglass, but instead of heatshrink it had a metal sleeve crimped on the end. Worked nicely untill the crimp came off. The thing I like about the beads is that they adjust more quickly, and read from a more clearly defined point.

Yep, thats true.

However the solid probe supplied with the datalogger (multimeter) which most of us use is only sensitive right at the tip... and reacts quickly to temp change as well. It also has a thermoset plastic (like bakelite) handle which isnt affected by heat. It is long enough to go through the side of the BM and about 1.5cm into the bowl.

Works really well (check out the dattalogger ZIP files for some examples.) Because you are measuring primarily the air temperature between the beans it is only a relative indication of the temperature inside the bean (which is what you really need to know :-/)

[Brekel]

Re: new controlled roaster

Thanks for that. the thermocouple Ive been using untill now was fibreglass, but instead of heatshrink it had a metal sleeve crimped on the end. Worked nicely untill the crimp came off. The thing I like about the beads is that they adjust more quickly, and read from a more clearly defined point.

[JavaB]

Re: new controlled roaster

Firstly, what type of thermocouples do most people use? The bead type or the solid probe type?
Brett.

Brett

Good to see another interesting project.


I use both types.... mainly the solid probe now with the Corretto

Ive seen a few photos in different posts where people have used the cheap probes supplied with some multi-multimeters, however despite the instructions which quote the instruments measuring range, the insulation on many of the probes is only rated to between 200º and 250ºC, which is cutting things a bit fine. The fibreglass insulated ones go a lot higher - does anyone know if there is any problems with these?

The general problwm with the bead probes is the end of the fibreglass is held in place with a piece of heat shrink tubing... which wont take even 200 deg for long. If you remove the heatshrink (and allow the end of the fibreglass to frey.... they work fine at roasting temps. You can even feed the probe down a length of thin copper or brass tube (after taking off the heatshrink) and just have the bead poking out of the end - that works fine!

I was also wondering how most people hold their probes in position: through a hole in the base of the BM/Pot/Whatever, or enter from the top and fix it in position somehow?

Yep solid probe inserted through the wall of the BM and through the bowl (just got to remember to pull it out before removing the bowl :-[) About 1 cm above the base of the bowl. You can also use the probe inside the pipe detailed above and insert it from the top with some sort of clamp to hold it in place.

Another question concerns the heating profile. Ive heard two different schools of thought, and theres probably others too. One is that you heat to first crack as quickly as possible, whereas the other was to heat quickly to 110, then slowly to 350, then quickly to 1st crack (supposedly reduces acidity?). Wondering what peoples opinions/experiences on these or other alternatives are?

Well I try to heat fairly quickly to first crack (about 195-200C) and then reduce the heat and coast into the second crack....

BUT

If you heat too quickly the temp just keeps increasing (residual heat in the beans, bowl- whatever) and you are into second crack straight away even if you back the heat right off...

You should really get to second crack at about 14 minutes for best flavour..... Im still adjusting my heat output before first crack to be able to achieve that.

[Brekel]

Im working on a new roaster, which will be powered from my heatgun with some feedback from two thermocouples to alter the output.  Ive just got a couple of questions.

Firstly, what type of thermocouples do most people use?  The bead type or the solid probe type?  

Ive seen a few photos in different posts where people have used the cheap probes supplied with some multi-multimeters, however despite the instructions which quote the instruments measuring range, the insulation on many of the probes is only rated to between 200º and 250ºC, which is cutting things a bit fine.  The fibreglass insulated ones go a lot higher - does anyone know if there is any problems with these?

I was also wondering how most people hold their probes in position: through a hole in the base of the BM/Pot/Whatever, or enter from the top and fix it in position somehow?

Another question concerns the heating profile.  Ive heard two different schools of thought, and theres probably others too.  One is that you heat to first crack as quickly as possible, whereas the other was to heat quickly to 110, then slowly to 350, then quickly to 1st crack (supposedly reduces acidity?).  Wondering what peoples opinions/experiences on these or other alternatives are?

Thanks,
Brett.