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  • New Rotisserie Oven

    Well after participating in some discussion re the differences between fluid bed (which the Corretto is - sort of) and drum roasters...... and having the subject raised on the CS visit to 5 Senses-

    I decided to make a drum roaster.....

    First take one quite old rotisserie built some years ago by Hotpoint. Picked it up second hand for very little. It is a small unit but very solid (which I figured would be good for heat retention). It has a grill opening at the top.... unusual but hey, just block it up!



    It had two 300W elements on the bottom and two 450W ones on the top..... now heat is needed where the beans are - so swapped them over. Tried the oven - the thermostat switched on and off with a large gap between the functions..... and the oven couldnt make 250C.... MMMMM not hot enough.... so thermostat had to go.

    It was replaced with my original "mock up" triac controller so the elements were always on... Tried again and bingo- I could easily get the oven to 260C+ and maintain it..... Looking good. I had the TC probe inserted through a hole in the back just slightly below the level of the rotisserie to monitor the temperature.



    The "control box" is a bit rough... but for a prototype The left hand knob gives 12 levels of heating.... the right hand one is continuously variable between the steps.

    Now for the drum.... I scored a Nescafe tin and did the normal cut and fold forming 6 internal stirrers (the motor only rotates at 2.5RPM).... and covered the outside with Stainless Steel mesh.... just held in place with PK screws : - but this will be refined later -mark II version .



    In this photo you can see the TC probe on the right hand side (the tip is held by a saddle clamp which it is fed through to hold accurately in position - right near the end of the drum so it almost touches.....

    First roast:

    Preheated the oven, set the temp at 240C, loaded 250gm of Monsooned Peaberry into the drum and let her rip!

    First crack was at 18 minutes with roast pulled 10 seconds into rolling second just before 20 minutes..... the roast looks good and the time is very similar to what I aim for from the Corretto except FC to SC is a little short. Beans were cooled by taking the rotisserie out and rotating in front of a fan..... and I could touch the drum after about 10 seconds.

    The beans look good... just have to wait a few days to taste.... should be an interesting comparison as I did a similar duration Corretto roast of the same beans just before this one.

    There is still some playing with temps etc.... but looks very promising.

    Will let you know how the tasting goes.

  • #2
    Re: New Rotisserie Oven


    Looks very good Java !

    Ive got a newer version of that type of oven which Ive wanted to modify like you have. Im not an electrician though.

    It will be very interesting to compare results.

    Do you reckon you can get to FC quicker?


    Belinda

    Comment


    • #3
      Re: New Rotisserie Oven

      Hi Belinda,

      Yep, there is a lot of capacity for heating the roast faster. To maintain 240C the switch was only at level 5..... so four more "hotter" steps to go. The oven goes to well over 260C (I stopped there because I wasnt sure what would melt :-/).

      So I will be aiming at higher power / temperature initially to speed up the roast, and then return back to the normal temperature approaching FC and then lower again FC to SC (as I do with the Corretto)....

      There was less smoke than with the Corretto, and the rolling SC was unbelievable... went from an occasional crack to a thunderous roll in a couple of seconds (I guess because of the more even temperature)... The sound of the cracks is even clearer than with the Corretto as there is no noise - at all - from the oven.

      But Ill reserve judgement on their relevant merits until I taste the result..... only a couple of days now .

      Comment


      • #4
        Re: New Rotisserie Oven


        Sounds interesting.

        It will be nice to have 2 methods of roasting. To suit your moods :

        Now Im inspired to have mine modified

        Do you plan putting a few more thermocouples into the oven to check out that more even temperature theory?

        Keep us informed!


        Belinda

        Comment


        • #5
          Re: New Rotisserie Oven

          Originally posted by Corretto link=1179926707/0#3 date=1179963943

          Do you plan putting a few more thermocouples into the oven to check out that more even temperature theory?

          Keep us informed!

          Belinda
          Belinda

          I would dearly love to put a thermocouple in with the beans.... but there is no way of doing it. That is a huge advantage with the Corretto - you are actually measuring the bean temperature - or pretty close to it.

          There is a temperature gradient in the oven (hotter towards the top) which I have already found. So at the moment Im measuring the temperature just below the rotisserie shaft - which would be just a little above the bean mass. The tip of the probe almost touches the rotating drum..... but I have no idea of the actual bean temp..... and cant see how I could do it either :-/

          The time I got on the first trial run was very similar to the Hot-top (which also does 250gm maximum roasts)... but as Luca says " its whats in the cup which counts".

          5 Senses are spending heaps buying a specially developed roaster which allows them to dial in a mix of fluid bed and drum roasting.... as the thought is a mix of the two techniques (probably a different mix for different beans) will produce the best flavour.....

          Now maybe if I convert the oven to a fan forced rotisserie oven..... :

          Ahhhhh the joys of experimenting.

          Comment


          • #6
            Re: New Rotisserie Oven

            Tinkerers just cant stop tinkering JB ;D

            While I was reading your post above I immediately thought of the possible benefits of making the unit "fan-forced" and reading further down, youve had the same idea LOL :. This type of design really lends itself to PID control in a big way too.... Yet more tinkering possibilities

            Mal.

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            • #7
              Re: New Rotisserie Oven

              It is possible to make a dual contact point with brushes that rotates on the axis of the shaft - difficult but possible.

              Comment


              • #8
                Re: New Rotisserie Oven

                Originally posted by grendel link=1179926707/0#6 date=1179998406
                It is possible to make a dual contact point with brushes that rotates on the axis of the shaft - difficult but possible.
                Well, yes, it is possible..... but the slip rings and brushes would have to be made of exactly the same material as the two leads of the thermocouple.....

                Otherwise you have extra junctions of dissimilar metals.... when generate voltage when heated..... and make the reading worthless...

                So it would be very, very hard!

                Comment


                • #9
                  Re: New Rotisserie Oven

                  2nd set of leads from Jaycar. . . hmmmmm he thinks.

                  Comment


                  • #10
                    Re: New Rotisserie Oven


                    Looks great JavaB.

                    I do love roasting contraptions... more the merrier.

                    If you make one end of the drum a cone it will allow you to move the (left) drum support further in and get a probe into the bean mass beside the shaft.

                    ------------------------
                    /\/ | |
                    /\/ | |
                    | |
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                    ---------- | |
                    / | |
                    / | |
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                    My acsii art is a little rough but with a little imagination it makes sense.

                    Comment


                    • #11
                      Re: New Rotisserie Oven

                      I friend and I made a similar one using a jam funnel at one end for easy unloading.

                      One funnel pointing in and one pointing out would allow for easy loading & bean probe and easy unloading at the other end.



                      Comment


                      • #12
                        Re: New Rotisserie Oven

                        Ah, thanks Andy....

                        I see what you are suggesting and makes good sense.

                        I had thought about having a "spider" inside the drum (in from one end) to support the drum on the shaft at that end..... and then having a freely rotating end to contain the beans..... that end would then remain stationary and a probe could be inserted through the stationary end into the drum (similar I guess to the front of a commercial roaster.....)

                        The probe would stop it rotating.... when roasting was finished pull out the probe and then the whole drum..... and empty as normal.....

                        But your idea would be less mucking about and probably more effective.

                        Cant beat experimentation.

                        Comment


                        • #13
                          Re: New Rotisserie Oven

                          Hey Java - this looks like it can handle a lot more than the 250gm youve tried. Have a few questions:

                          What do you think might be an optimum weight that you could roast?
                          Would you try it without pre-heating the oven...so that the beans might go through a drying cycle?
                          Whats the effect re chaf - does it burn off?

                          Looks like fun and I just love the fact that a nescafe tin is a component !!

                          Comment


                          • #14
                            Re: New Rotisserie Oven

                            Dennis,

                            Yep it would take at least 600 grams - possibly more. Ill be experimenting to see how the roast times are affected by bigger loads. Once Ive done some more testing Ill have some idea of its actual potential.... but Im waiting to taste the first roast..... not much longer now!

                            I can heat the oven as little or as much as I want (far more control than the thermostat...) so I will give the drying cycle a try.... the only problem is if you dont get them to first crack in a reasonable time you can end up with beans which taste baked.... so again some experimentation is called for.

                            Most of the chaff falls out through the gaps on the drum onto the base of the oven - and just sits there and slowly goes brown - some hits the elements and is incinerated.... and a bit remains in with the beans.... a quick pour between colanders in front of a fan soon dispatches those.

                            And the Nescafe tin.... yep, appealed to my sense of humour as well.

                            Comment


                            • #15
                              Re: New Rotisserie Oven

                              Well tasting of the first oven roast has now started.....

                              So here are the first details of the comparison between a Corretto roast and the oven drum roast.

                              Both were used to roast 250 gm quantities of Monsooned Peaberry.

                              The beans were roasted in roughly the same time (just under 20 minutes to SC) and the roast pulled at the same stage (about 10 seconds into SC)....

                              Beans were the same colour and evenness of roast in both cases.... and developed some small patches of oil on the surface during resting.

                              The oven roast produced a darker (and slightly more abundant) crema than the Corretto..... the grind needed to be slightly coarser as well for the standard pour.

                              In the cup, the flavour of the oven roast is more intense, but lacking some of the subtle flavours which I find very pleasant with the Corretto roast. It is also slightly less sweet on the palate as well. The slight "roughness" of the oven roast is similar to a Corretto roast which has only be rested for half as long.

                              Im beginning to think that oven roasting requires a longer resting time to develop to its peak.... so it will be interesting to see how the flavour develops over the next few days.

                              At this stage (and I have to do some more testing - this being my first oven roast) I find the Corretto roast far more interesting and pleasant - at least to my palate...

                              Will provide further feedback as the oven roasted beans rest for more time.

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