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  • new controlled roaster

    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.

  • #2
    Re: new controlled roaster

    Originally posted by Brekel link=1163049397/0#0 date=1163049397

    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.

    Comment


    • #3
      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.

      Comment


      • #4
        Re: new controlled roaster

        Originally posted by Brekel link=1163049397/0#2 date=1163051934
        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 :-/)

        Comment


        • #5
          Re: new controlled roaster

          Originally posted by JavaB link=1163049397/0#3 date=1163052655

          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.
          Brett I agree with almost everything JavaB wrote. I did actually melt the bakelite when I was trying to calibrate the probe with boiling water and 100 is a lot less than 230. I had it attached to the side of the saucepan and it did not like the heat one little bit.

          That said I havent had a problem with the probe inserted through the bread maker, it doesnt get hot at all, sometimes I have to hold it in place because the beans get a bit excited and knock it out of place.

          Comment


          • #6
            Re: new controlled roaster

            Originally posted by Brekel link=1163049397/0#0 date=1163049397

            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?

            Brett.
            I soldered a length of 8mm diameter copper tube to the exterior wall of the BM, intruding into the cavity, stopping just short of the mixing bowl(so I dont knock it off each time I dump the beans), I have had better results from the solid probe, the flexible one seems to have broken some how, it only reads "1" after start up, I wonder if I can snip the end and start again. :-?

            Comment


            • #7
              Re: new controlled roaster

              Snipping the ends should be fine, as long as you can join the wires reliably. Theyre normally welded with a special capacitive discharge arc welder. I wouldnt solder them - at the temps were talking about, it wouldnt be reliable. Plus lead and food dont mix that well.
              As long as youve got a good junction between the two dissimilar metals, the thermo-electric effect will occur.

              Comment


              • #8
                Re: new controlled roaster

                Originally posted by Brekel link=1163049397/0#2 date=1163051934
                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.
                What we used to do with these, is to make a ferule out of fine fuse wire that is wound around the external f/glass sheath and over-lapping to where the two t/c cores exit the sheath. This is then soldered to form a solid ferule that will withstand temperatures up to the melting point of the solder, well within the boundaries of coffee roasting .

                Mal.

                Comment


                • #9
                  Re: new controlled roaster

                  Originally posted by Brekel link=1163049397/0#6 date=1163070292
                  Snipping the ends should be fine, as long as you can join the wires reliably. Theyre normally welded with a special capacitive discharge arc welder. I wouldnt solder them - at the temps were talking about, it wouldnt be reliable. Plus lead and food dont mix that well.
                  As long as youve got a good junction between the two dissimilar metals, the thermo-electric effect will occur.
                  Great, now Ive got enough foreign words to justify a trip to bunnings

                  Comment


                  • #10
                    Re: new controlled roaster

                    Originally posted by Mal link=1163049397/0#7 date=1163087410
                    ...This is then soldered to form a solid ferule that will withstand temperatures up to the melting point of the solder, well within the boundaries of coffee roasting .

                    Mal.
                    Youd have to be carefull with this. Although soldering is normally done at 300-400ºC, the solder actually begins to melt at around 183ºC.

                    Comment


                    • #11
                      Re: new controlled roaster

                      Originally posted by Brekel link=1163049397/0#9 date=1163108620
                      Youd have to be carefull with this. Although soldering is normally done at 300-400ºC, the solder actually begins to melt at around 183ºC.
                      Yes,

                      Youre quite right there Brekel..... we used to use a eutectic higher temperature rated solder from memory (Sn05Pb93.5Ag1.5) which has a melting point nearer 300ºC and as you say, standard solder would probably be unsuitable if it is likely to be directly exposed to the temperatures experienced in roasting. It was my impression though that the termination of the sheath of the t/c would not be so exposed and that only the junction itself would be immersed in the bean mass.

                      I think you can also obtain heat-shrink that is rated much higher than the standard variety available from DSE et al that is used in industrial applications.... So long as it isnt directly immersed in a flame it is capable of withstanding temperatures up to 300ºC. Industrial Electric Motor Rewind facilities would use this, as would some of the Refractory Furnace manufacturers who may be able to sell you small off-cuts, or maybe even give them to you.

                      All the best,
                      Mal.

                      Comment


                      • #12
                        Re: new controlled roaster

                        Yep, that kind of solder would do it nicely.  Until I work out exactly where my thermocouple will go, Im not sure exactly how much will be exposed, so I want to keep my options open.  Im also putting a second thermocouple into the incoming airstream, so the microprocessor will have an extra variable to work with and hopefully be easier to achieve the desired profile.

                        Does anyone know of any sites where you can see profiles for professional roasters?  I thought that kind of info would be a good startng profile to emulate initially, and then experiment from there.

                        And yes, as time allows Im wading through the 17 pages in the Datalogged zip file threads - theres a lot to go through though!

                        Comment


                        • #13
                          Re: new controlled roaster

                          Originally posted by Brekel link=1163049397/0#11 date=1163154251
                          Does anyone know of any sites where you can see profiles for professional roasters? I thought that kind of info would be a good startng profile to emulate initially, and then experiment from there.
                          Dont know if this is the sort of thing you are looking for Brekel, but as you say it might get you a foot in the door to repositories of more explicit information about the topic.....

                          Heres a couple more..... Here, and here.

                          Hope some of this is helpful,

                          Mal.

                          Comment


                          • #14
                            Re: new controlled roaster

                            The last link you posted Mal is an article written by the only other owner of a Gothot Sample roaster like mine that Ive been able to locate and actually talk too. I dream of the day my roaster has been moded to the level that his has been. He has quite the set-up, some of which you can see here including several shots of his Gothot: http://www.sweetmarias.com/hondurasCoEcupping2004.html

                            He has written several articles on roasting that make for enlightened reading and has them posted on his site here: http://www.bootcoffee.com/articles.html


                            Java "Wants that temp control!" phile
                            Toys! I must have new toys!!!

                            Comment


                            • #15
                              Re: new controlled roaster

                              Thanks for the links guys! Looks like theres some interesting info there. When I start putting things tohether, Ill let you know how I go.

                              Comment

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