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  • arcticroaster
    replied
    Re: temperature for roasting in corretto

    Originally posted by JavaB link=1167177851/30#30 date=1167788268
    Hi Peter,
    The heat gun adjustments required around and after FC are very fine... and I doubt you will be able to make them with a standard heatgun - well not without a lot of pain.
    Hi JavaB,

    I did a bit more fiddeling with my HG to understand the control better. Temp is controlled with a large dial with has many "teeth" (can be seen on the the pics I posted earlier).
    Couple of observations from measurements (TC in front of nozzle, outside the bowl) in the 60 .. 75% power range:

    1) when stepweise increasing power by advancing by one tooth, temp rises quite consistenly by 10 deg after some time lag

    2) its impossible to map these dial position to **absolute** temps. Eg when running the HG for some 15 min temps were 10 .. 20 deg higher (gun heats up, maybe the control Triac circuit is is temp sensitive, resistance of TRIAC may chnage, 1000 effetcs etc)

    3) when changing control direction from eg up to down , there seems to be some hysteresis before the HG responds  with appr. 10 deg down steps. You have to dial back 2 .. 3 teeth for that. I also read somewhere that certain Triac "dimmer" circuits have such hysteris behaviour

    4) when giving over some time up and down commnads , the temps come always out a bit different. However, smaller **relative** temp up/down changes are consistently possible with these caveats

    I tend to believe that in my case building external TRIAC dimmer circuit makes not much sense. The HG appears to already have a basic dimmer circuit  type of control, although with only one potentiomenter moved by the dial. So I already get roughly 10 deg steps control, just like at above mentioned Steinel HG and incidently like your external circuit (power change with 10 deg at 250 deg operating temp = 10/250 = 4%). And different control circuit doesnt help against the thermal lag and need to "plan ahead" with the temp settings, which, in this case I suppose means that when during the exotherm phase of 1st crack the beans produce heat and increase temp you should probably *increase* the temp by one notch in anticipation of the heat absorbing phase coming in 30 sec later or so , etc.

    Now being better aware of these issues you mentioned my last roast went roughly like this (sorry no nice log file yet):
    start of 1st crack  around 7 min @ 199 deg,
    8 min:  209 C
    9 min: 216 C
    10 min 220 C
    11 min 224 C sencond crack starts
    12 min 228 C, roast off  

    So between 1st & 2ncd crack I have initially a slope around 10 deg/min, then down to 4 deg/min until the end. Does this look reasonable ?

    I used some peruvian beans, is endothermic behaviour very bean specific, ie are some beans more prone to stall than others after 1st due to high heat absorption ?

    Anyway, I am almost exclusivley using these beans, its a workmate who runs a specialty coffee as 2nd business in his "free time", so its very convenient for me to get the beans from him (and they are good for espresso roasts). So maybe with some more roasts I will learn to manage the temp behaviour of these beans together with all the thermal lag in the control loop. Well, thats the main fun of this whole home roasting, cranking the HG controls around like mad and yet having in the end a decent cup and being able to do roast profiles which even a professional Probat roaster owner cant do (with larger charges) and all this with a heap of kannibalized home tools for a few bucks ...  

    Sorry for putting you all asleep with these tedious ramblings, every Coretto-roaster wonders probably since hours why the heck arcticroaster is not backing off his HG, there you got your nice continous control of flow an heat without any fancy TRIACs or whatever, but the sad truth is in my setup backing off the HG is not an option: the lid is in the way of the nozzle and I would loose all temp readings as I would be pulling out also all TCs as well ... :

    Cheers, Peter

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  • JavaB
    replied
    Re: temperature for roasting in corretto

    Originally posted by arcticroaster link=1167177851/30#32 date=1167849881
    JavaB, looks you are already pretty much down the road to upgrading the "Coretto" into a precision profile roaster , you got all the sensors with data computer uploading, you got 100% electronically controlled super fine heat adjustements , you got possibility for electronic activation of the cooling cycle ... hey, wait, makes me wonder if you are already working on a PID controller and hooking the whole thing up to your laptop, from which you only need to mouseclick on a predefined roasting profile from your favourite sofa or why not via cellphone during the drive home

    All the best,
    Peter
    HeHe.... very true- I had thought of automating the setup - but that would remove half the fun! Its one thing to have good tools to do the job - its totally different if you have someone (or something) do it for you!

    Im not sure how fine the adjustment of even the best heatguns is..... after all they werent designed with this sort of precision in mind. Air flow variation is a possibility but I would imagine reduced airflow would increase the temp of the air out of the gun..... but transfer less to the beans.... hard to work out what would happen!

    The other method which doesnt require a mod or an expensive gun is to change the distance - and this doesnt have to be by a lot to change the amount of heat transferred. So maybe a combination of coarse steps on the gun and fine adjustment by distance changes and you would get the same effect.

    By the way, distance changes dont suffer the same amount of lag that changing the heatgun power does...... another possibility.

    Leave a comment:


  • arcticroaster
    replied
    Re: temperature for roasting in corretto

    Originally posted by JavaB link=1167177851/30#30 date=1167788268
    Hi Peter,

    The heat gun adjustments required around and after FC are very fine... and I doubt you will be able to make them with a standard heatgun - well not without a lot of pain.
    Hi JavaB,

    hhmm, you maybe right, I already had the sneaking suspicion when looking at the heat output vs dial settings of my HG as posted above, ie 60 deg change for just changing dial from 6->7, how to hit your 4% heat output change with that ...   ;D

    But in addition to your solution there may be some other options:

    1) getting the Ueber-HG from control point of view http://www.steinel.de/en/thermo_fuer...se/hg_2310_lcd, but then again temp changes may in steps of 10 deg only (at least for their similar models) and fan-step changes are not clear form this. Also risk is how such HG would adjust internally the temp settings when you change the fan speed (otherwise temp rises), so there may be some iffy transients depending on their logic, how should one know this beforehand ? And this thing is spendy (~100 EUR). In principle I like the idea though of fan speed changes in this very convection oriented setup of mine (faster reaction times?)

    2) I could split the heat supply between HG and the gas burner and then do the finer adjustments on the gas burner in/after FC. But I havent tested this yet properly, ie how much extra heat is still required from HG when the burner is in low-moderate settings. Dont know if the burner adjustments are any faster as the bowl has some thermal inertia. Anyway the burner setting needs some headroom for up/down changes, so I may end up running the thing in drum-style roaasting only with little convection.

    I think your mod may not be all that tricky, a quick search showed there are ready-made TRIAC controller modules around for some EUR 20, you only need to add 1 .. 2  potentiometer for course/fine control and thats it.

    Need to ponder all this further.

    JavaB, looks you are already pretty much down the road to upgrading the "Coretto" into a precision profile roaster , you got all the sensors with data computer uploading, you got 100% electronically controlled  super fine heat adjustements , you got possibility for electronic activation of the cooling cycle ... hey, wait, makes me wonder if you are already working on a PID controller and hooking the whole thing up to your laptop, from which you only need to mouseclick on a predefined roasting profile from your favourite sofa or why not via cellphone during the drive home 

    All the best,
    Peter

    Leave a comment:


  • grendel
    replied
    Re: temperature for roasting in corretto

    I think JavaB is the Heat gun mod god after that bit of work.

    Leave a comment:


  • JavaB
    replied
    Re: temperature for roasting in corretto

    Hi Peter,

    Im glad Belinda and I were able to help.

    The heat gun adjustments required around and after FC are very fine... and I doubt you will be able to make them with a standard heatgun - well not without a lot of pain.

    Part of the problem is the thermal lag... the effect of any change isnt visible on the probes for 20-30 seconds (in my corretto) so you firstly need to get a feel for what is required that far in advance or you will overshoot or undershoot the correction.

    Ive modified my heatgun for finer control - if you have a friend who is an electrician you could do the same.

    Firstly I opened the heatgun (voids the warranty) and identified the heating circuit. I then built a 16 amp triac "light dimmer" with 12 switched stages of output between full and about 60 deg C output.... (using 11 equal resistors to set the output of the triac) and connected it externally to the heating circuit.

    That improved the control of output a lot - but I still found it a bit coarse.

    I then installed a potentiometer (variable resistor) of the same value as each resistor.... so one complete turn of the potentiometer gave 1/12 of the heat range...

    Now I control the temperature from first into second crack with the variable control (temperature up to just before first crack with the switched control). I find the variation required to be about half a turn of the knob on the potentiometer - or about 4%...... and you wont get that with any standard heatgun.

    I can even maintain the temp at a constant setting by fine adjustment of the potentiometer - and providing I allow for the thermal lag of the roaster.

    Total cost of the mod was about $20 .... and I think it will also extend the like of the heatgun heaps - it is hardly ever "flat out" and at the end of the roast I can turn it right down to cool down the gun.

    I even used the lowest setting (60C) to cool the beans in the corretto once. It worked well - took a little time to cool them down- but is possible. You just have to start the cooling a little earlier as the beans will continue to roast a bit.

    So if you have a mate who is an electrician ..........

    Leave a comment:


  • arcticroaster
    replied
    Re: temperature for roasting in corretto

    Belinda and JavaB,

    thanks a lot for this extremely informative Correto handling info . Especially JavaBs post-FC HG handling tricks is something I need to try, because I exactly have these temp run-away situations above 210 and around start 2nd which I have not yet mastered properly in terms of heat reduction. This is because I earlier stalled the roasts after FC (or had constant temp for some 2 min or so), so I tend to add too much heat arounf FC and miss the reduction point before/around 2nd. I mean the roasts are pretty OK, no charcoals by any means, but I understood that for Espresso roasts you should have the caramelisation go in a very gentle & controlled manner (slow linear(?) temp rise to say ~230C). OK, that needs lots of practice and I also need to investigate carefully how actually my probably China-made HG really changes the outlet temps as function of the dial settings (and in which time/transients). I dont trust that beast, in my last roast I still got the thermal runaway even though I did drastically ramp heat done, late in the game though around 220C. Probably ideally would be for me a HG where you can keep temp=const but change the airflow instead ==> better instantaneous control ??as I cant backoff the HG or I loose all TC readings (Steinel has a wonderful HG gadget for this for ~100+ EUR),

    Then, Belinda, I amust say I am amazed how even the temps are in the Coretto and its cool how they even compltely equalise in FC. I guess you must get nice even airstream from HG and the stirrers seem to take care of the rest. And you dont get these very dissimilar bean speeds in the bowl as I get them, so I guess your whole bean surfcae can absorb about same amount of heat.

    The overall temp ranges (bean vs air) you mention for the Coretto seem to be quite in line with measurement I took lastr night - so my cementmixer-roaster is not as badly behaved as I feared. I was only looking at the HG polluted TC reading which scared me, but when taking all 6 TC readings then the picture starts looking actually not all that different from what you said.

    In the next pic below you see last nights recording just prior to FC. This slow-shutter pic first gives you an idea hwo the beans flow and at whcih speed. The bowl is 45 deg inclined so the beans just flow fast downhill form 1oclock to 7oclock direction. This is like a fluid-bed and I have now re-arranged the heat gun nozzle so as to cover this fast moving "river" at as indicated by the pink ellipse (~5.5 cm above beans). The "hot" TC named L2 is close to bottom of beanbed and without bowl, is not be hit by the airstream, i.e. stays cool (50 deg at full HG blast). However, here the bowl creates (so I guess) a hot air plume which causes this high reading , actually very close to the situation without any beans in bowl (about 265 deg). So we see that the bean-river doesnt cool the HG airflow any more (unlike in beginning óf roast) and temps were rising slowly at this moment. TC called R2 is about 1 cm into beans and seems to be a very good "average" indicated it registered FC around 200C and should be the main aiming point. The 55 deg offset between L2 and R2 was almost kept throughout the entire roast.

    The rest of the TCs are about 1 .. 2 cm above the beans (due to the vanes interfering) .

    This roaster seems to work like a cross-flow heat exchanger: the concentrated HG air stream hits the (circulating) bean-mass flow and transfers heat to it. And there is always this mysterious 55 deg difference between the hot medium (HG air) and the warmed beans (cool medium) at their respective heat exchange "outlets". Probably this difference is always needed to compensate all the other heat losses in the roasting chamber.

    I almost panicked when L2 was recoring 270 C around 2nd and thought that the roast must be very uneven now. But it was perfectly even. No charring, with 270C at 5.5 cm and HG with max airflow .. : Only explanation is then that this bean fluid-bed with all the tumbling is so effective in heat transfer, like in real air-roasters where I heard temps well above 300 C are used.

    OK, sorry for this extremely verbose rambling, but I think now I get slowly the picture how these HG setups generally are meant to work. Then the next thing one should do is to actually start cupping the different profiles JavaB was hinting at and see how it ultimately pans out out in the cup.

    I attach below also 2 more pics from the latest incarnation of my TC instrumentation - maybe not releavnt for anybody here on the HG/BM Coretto trail, but maybe inspiring for people with other HG setups and something rotating beneath.

    All the best,
    Peter








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  • JavaB
    replied
    Re: temperature for roasting in corretto

    Java,

    Yep, Its strange.... but true :

    The heatgun blasts out far hotter air than a popper and is capable of carbon conversion in short order....

    One of my methods Ive tried:

    I start the HG relatively high up to about 150C then slowly reduce the heat so that it is heading to first crack in about 10-12 minutes (sometimes a little longer). By the time it is at the start of first crack the rate of temperature increase is slow.... but steadily increasing...

    When first crack is rolling nicely.... if I leave the HG output the same, there is a slight dip in measured temperature.... and then it starts to increase again at about 210C slowly at first. If I dont do anything it starts to race ever faster and faster up to > 230C with lots of smoke and the result is not pleasant....

    How do I know.... well you got to set up a base line measurement!

    So now (if Im using this method) I increase the HG output ever so slightly just after the start of first crack and then bring it back down (by quite a bit more than I had increased the output) at about 205C.... and let it coast toward second, slowly reducing further if required to maintain the nice slow increase until I reach the desired roast level (in a controlled way).

    So yep, quite a bit different to your method.... but I get the level of roast required in about 15-17 minutes (or any other time I choose). Thats what I love about the Corretto- fantastic control.

    EDIT: the other significant difference.... the corretto bowl is quite a bit cooler than the beans and is also stealing heat from them. In your roaster you have a considerable thermal mass which is quite a bit hotter than the beans.... and will continue to heat them for some time after you have reduced the heat source.

    In my case, only the heat from the gun is an input to the roasting process... the bowl is constantly cooling the bean mass - together with the fan blowing over the top of the corretto.

    Leave a comment:


  • Javaphile
    replied
    Re: temperature for roasting in corretto

    Its interesting how different systems are adjusted differently to end up at the same result.

    With my roaster I get a very visual image of just how much I have to reduce the heat at the onset of first crack as it is gas fired.

    In brief it is a gas fired solid barrel sample roaster (For all the details on it go here). On the way up to first crack the flames are 2-3cm high. When the beans enter first crack I have to turn the flames down so that they are barely able to stay lit (3-4mm). The exact timing of when the flames are turned down varies from bean to bean but it always occurs prior to the rolling first crack. If this is not done the beans will go straight from first into second crack.

    Most beans require very little additional flame after first crack to reach second crack 3 minutes after the end of first. Some on the other hand can require quite a bit. A surprising amount even when compared to most of the other beans. Many Nicaraguans seem to fall into this catagory.


    Java "Things that make you go Hhhhmmm...." phile

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  • JavaB
    replied
    Re: temperature for roasting in corretto

    Originally posted by Javaphile link=1167177851/15#24 date=1167735687
    Uuuummmm........Did you mean 2nd crack? At first crack the beans go exothermic before returning to an endothermic state.
    Java "Hhhmmm...Energy!" phile
    Java,

    I dunno

    According to sweetmarias:

    "Since first crack is an exothermic reaction, the beans are giving off heat in first crack, but the quickly become endothermic, meaning that a roaster that is not adding enough heat to the process will stall the roast at this point ...not a good thing. Once caramelization begins (340-400 degrees internal bean temperature) a roast that looses heat will taste "baked", perhaps due to the disruption on long-chain polymerization."

    Which suggests the transition occurs during first crack.... they mention a bean temperature of 370 degrees....(187C for us down under) as the start of the endothermic caramelisation reaction which is ..... before the end of first crack.

    That is also my observation.... there is a drop in temperature whilst in the first crack..... so up with the heat ever so little so the temp doesnt drop.....

    You can see that on some of my datalogger zip files...... a slight drop at about 195 C (air temp - not bean core temp) when I didnt correct for extra heat absorption.

    But if the heat isnt dropped back so you slide into second....
    Thermal runaway!!! Lots of smoke and charcoal real fast!!!!

    Leave a comment:


  • Corretto
    replied
    Re: temperature for roasting in corretto

    Originally posted by Javaphile link=1167177851/15#24 date=1167735687
    Uuuummmm........Did you mean 2nd crack? At first crack the beans go exothermic before returning to an endothermic state. As they crack they are releasing energy. This is why you have to be careful of a roast running away and going straight into second crack.
    Java "Hhhmmm...Energy!" phile
    This would explain why at first crack the temp seems to even out from top to bottom.


    Belinda

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  • Javaphile
    replied
    Re: temperature for roasting in corretto

    Originally posted by JavaB link=1167177851/15#23 date=1167728351
    At first crack the beans become very endothermic absorbing lots of heat as the sugars get caramelised.
    Uuuummmm........Did you mean 2nd crack? At first crack the beans go exothermic before returning to an endothermic state. As they crack they are releasing energy. This is why you have to be careful of a roast running away and going straight into second crack.


    Java "Hhhmmm...Energy!" phile

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  • JavaB
    replied
    Re: temperature for roasting in corretto

    Originally posted by Corretto link=1167177851/15#22 date=1167725928

    I cant answer all your questions, maybe JavaB can help?
    OK, Ill add my 2c worth...

    I have tried various methods of roasting.... ramping up the temp to provide a constant increase, running with 250deg just above the beans.... and starting at different levels of initial heat and reducing after first crack. They all give slightly different results in the cup. The different styles seem to be more suited to different bean varieties as well. e.g. the constant 250 gives a longer roast and better flavour with Monsooned Malabar.

    I measure the temp about 1 cm above the base of the bowl and about 2 cm in from the side.... as far as possible from the heatgun. Directly under the heatgun - even only 1 cm off the bottom - some hot air penetrates the bean mass and increases the temperature.

    I agree with Belinda that it will be 15-20 degrees hotter in the beans just under the gun - but in all cases we are measuring the air surrounding the beans - not the actual beans.

    Just above the bean surface - under the gun - the temperature I use would be between 250 - 300 C at the maximum.

    In the corner - furthest from the HG it is probably about 50 C cooler - but still well above the temp 1cm from the bottom.

    And the bowl is also far cooler than the air temp because of radiation from its external surface.

    For the most part of the roast the difference between the 2 was about 15C with the top probe being the hottest. At first crack the difference changed to around 0C, sometimes with the bottom probe being hotter.
    At first crack the beans become very endothermic absorbing lots of heat as the sugars get caramelised. So more heat from the HG is being absorbed. If you dont supply enough extra heat the roast will stall and quality of the final product will be reduced (which is why I maintain at least 50 degrees of heat difference HG output to bean mass until after first crack).

    Some of the best roasts have been with the HG output - measured at the surface of the beans and directly below the HG - kept at 250 degrees for the whole roast.

    Try to measure your bean temps away from the HG blast and as deep in the bean mass as you can (without being closer than 1 cm to the sides or the bottom)- and remember the temperatures are not absolute as you are measuring air temp and not actual beam temp.

    Leave a comment:


  • Corretto
    replied
    Re: temperature for roasting in corretto

    Originally posted by arcticroaster link=1167177851/15#21 date=1167430104
    Hi Belinda,

    for curiosity about the inner workings of the "Coretto":
    - with your standard settings, what would be the air temp just above the beans when compared to the beans itself ? Is there some more or less constant difference as you heat up the roast ?
    - if you have final temp of around 220C , what would then be the air temp above beans (I assume you have HG still on ?)
    - Is the bean temp even, or does it depend much where you measure ?


    - with 10 cm distance of the HG, are you hitting only certain areas of the beans or do you get some mild airflow covering the whole surface more or less the same way ?

    Sorry for these many questions, but I am trying to figure these things out for my setup. The reason is that I got very different bean temp readings when I changed the TC location in my last roast which makes me suspect that I have quite some temp variations within the flowing beans. Actually, I suspect these readings were polluted by the hot&strong airflow from the HG and way higher then the average should have been.

    Cheers, Peter
    Sorry for the late reply Peter, but .... have been doing the nightshifts.

    I cant answer all your questions, maybe JavaB can help?

    I did a 630 gram roast the other day, the biggest so far. A blend.

    I had my normal datalogging probe ~ 2 cm off the bottom of the bowl on one side and had a non datalogging probe about 2 cm below the top of the beans on the other side.

    For the most part of the roast the difference between the 2 was about 15C with the top probe being the hottest. At first crack the difference changed to around 0C, sometimes with the bottom probe being hotter.

    Of course after 1st crack I wasnt taking as much notice of the top probe. But it is obvious there is a lot of mixing going on. Im thinking the difference in temp has something to do with why all the beans dont crack at the same time Id love to have more datalogging probes throughout the roast.

    I did a smaller roast ~ 224 grams and found that the difference between top and bottom started off at +15C for the first few minutes and went to 0C by 6 mins and then stayed + and - 5C approaching and post first crack. So obviously a lot of mixing is going on. All very interesting.

    Next time I will put a handheld probe into various locations of the roast and take some spot measurements.

    I have measured the temp just above the beans before and found it to be close to what I just measured 1 or 2 CM below the top of the beans.

    So there you go. Its all so confusing and the more you probe the more complicated it gets!

    Belinda

    Leave a comment:


  • arcticroaster
    replied
    Re: temperature for roasting in corretto

    Originally posted by Corretto link=1167177851/0#7 date=1167190381
    My HG is rated at 650C and I run it just below full power aimed about 10 cm above the beans.  This translates to heating the beans to a final temp of around 220C  8-)
    Hi Belinda,

    for curiosity about the inner workings of the "Coretto":
    - with your standard settings, what would be the air temp just above the beans when compared to the beans itself ? Is there some more or less constant difference as you heat up the roast ?
    - if you have final temp of around 220C , what would then be the air temp above beans (I assume you have HG still on ?)
    - Is the bean temp even, or does it depend much where you measure ?
    - with 10 cm distance of the HG, are you hitting only certain areas of the beans or do you get some mild airflow covering the whole surface more or less the same way ?

    Sorry for these many questions, but I am trying to figure these things out for my setup. The reason is that I got very different bean temp readings when I changed the TC location in my last roast which makes me suspect that I have quite some temp variations within the flowing beans. Actually, I suspect these readings were polluted by the hot&strong airflow from the HG and way higher then the average should have been.

    Cheers, Peter

    Leave a comment:


  • arcticroaster
    replied
    Re: temperature for roasting in corretto

    Originally posted by nunu link=1167177851/15#18 date=1167354590
    Hmm...looks to me like the stated temps may be in Fahrenheit.  Convert the actual temp at the nozzle to degrees Fahrenheit and you have an approximate match.
    Should be deg Celsius according to the HG specs.

    One reason for the substantial temp drop I measured may be the holes (on both sides) close to the inlet of the nozzle, see the pic. I could imagine that the fast rushing hot air would suck then outside air into the stream ("bernoulli effect") and as I was measuring at -2 deg C outside temp maybe this cooled things down a bit. So to advance the HG science, I may re-do above table without the nozzle, ie right at the HG outlet - or has anybody done such exercise already with possible higher rated TCs ?

    If this was the reason, then inside my roast chamber I shouldnt get such a large temp drop as the hot chamber aitr would get sucked in / re-circulated. Once again, it all points into ditrection of measuring the temps right inside the roaster setup as there are quite many effects coming together ...

    Cheers, Peter

    Leave a comment:

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