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Thread: Roasting slow-fast profile in the KKTO

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    Senior Member readeral's Avatar
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    Roasting slow-fast profile in the KKTO

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    I'm really struggling to retain any aromatics in my KKTO roasts, and maybe 1 in 10 roasts has the fruity acidity I'm so keen to find. It might be to do with too high a heat level and possibly an airflow thing, but I'm not experienced enough to troubleshoot. I'm sure it's just my skills lacking, but I'm almost inclined to stop searching and just resign myself to darker cocoa-like roasts. It's a bummer, given the tantalising descriptions Andy puts on these coffees. I know it's in there, just a bit too amateur to make it happen!

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    Mal Dimal's Avatar
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    Do you have any roast profile samples that you could post up Al?
    Might help us to try and help you...

    Mal.

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    Senior Member readeral's Avatar
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    Sure, I'll prepare a few of my recent ones. TBH, it's my first winter of roasting in the KKTO (last winter it was a popper), so that's also thrown me a little.

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    Senior Member readeral's Avatar
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    Ok - here's a bit of a recent cross-section.
    First is a Mexican, 600g batch, which has been my most consistently successful bean to roast this year. Been awesome. Sadly, I just ran out. Alas. I enjoy roasting this bean, and the results. It seems to like the high temperatures pretty well.
    Mexican.png


    Second is a Peru 600g batch
    Peru.png

    The next 3 I roasted this week, and have lowered my charge weight from 600g to 500g to try have a little more energy in the system, and to control it better. So, as you'll note, I've dropped my environment temperature from 265 down to 250/255 range.

    Peru 2 - this one I was trying to push through to a 2nd crack, but it actually ended up not getting anywhere close, and I had to drop it as a light/medium roast.
    Peru2.png

    Ethiopia:
    Ethiopian.png

    Rwanda:
    Rwanda.png

    I'm conscious that the transfer of heat into the bean is not just a matter of environment temperature, but a combination of airflow and available heat (as well as bean density etc. obviously playing a part) but right now I don't have control over my air speed, only my element, which I still haven't wrapped my head around PWM to keep it at a constant power level (it still pulses on and off once it reaches my PID preset of 265/250-255). That's a project for once my sparky friend has a little more time to help me.

    I also have been preheating to a stable 265 degrees, which might be a bit too much, but I haven't been getting any tipping or scorching, so have kept it there. I've been finding that 250 can do the job, but really only if I drop my charge weight. Part of me suspects that it's with the high drop in temperature that I might be losing my volatiles and aroma.

    The final thing is that my bean thermocouple seems to have shifted in the past 6 months. I used to hit 1st crack predictably on 200 degrees, but now it comes around 205. Hard to know if it's the thermocouple, or if it's a delayed (by temperature) 1st crack due to too high temperatures, that is, by the time I start to hear the cracking (which may have started at 200) the system has already reached 205. *shrug* excuse the overthinking after a day full of assignment writing.

    Lastly - I have a flat burr grinder. Won't make much difference, but will have a slight impact in how the flavours make it into my cup. I use a Hario hand grinder for my cupping, but haven't been inspired to do that in the past few months.

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    readeral, just my thoughts coming from 2000+ sample size drum roasts using the style of roast you seem to be chasing.

    You mention airflow control, this is critical to balancing the environment temp with the bean temp rate of rise. Also I do not think your elements going ON / OFF is ideal for this style.

    The first profiles I was thinking crikey you are spending a LONG time at 265 environment temp while going through the 150 to first crack zone. Straight away I was thinking ashy caramels / baked.

    The start of the roasts, up to 150 look really good. However they are out of proportion to the rest of your roast = the really long time you are taking between 150 and first crack.

    The start of your roast is quite aggressive and you are probably getting plenty of early roast development. With such a start I would be expecting to hit first crack start around 9 mins - with a steadily declining curve, slowly dropping environment temp = gently teasing heat from the system while keeping this balanced with ever increasing airflow = more convection as the roast nears the end. This requires one to have built up some thermal momentum earlier on to coast on.

    Off the top of my head from what I have seen / read and used a turbo oven for general cooking. I would say abandon your fast start and try for something along the lines of a slow start / fast finish profile - google it.

    Generally, take your time gently teasing out the moisture the from seeds until they are yellow, environment starting 200C very slowly rising. The curve will flatten slightly - like what others are calling the seattle dip.

    Ramping the heating up progressively to hit your max environment temp - say 250 - 255 around 8min mark. Hold steady until first crack is really going then gently wind back to find your optimum finish. If it is for manual brewing try dropping at the end of first crack, then another roast +30sec, +45, +1 min and so on. Otherwise find what gives you 3.5 to 4 mins to start of second for espresso and work backwards.

    If your roast times are overly long (FOR ME anything over 14 - 15 min is more of a bake) and you want to shorten them up, just keep reducing batch size while keeping your environment temp targets the same.

    Eventually you can wind back to where you can pull off a pretty much " straight line " profile to first crack start, then tapering off with a declining ROR for the finish, which in my experience is where it matters the most. I have done tones of experimenting comparing slow start / fast finish with a declining rate of rise finish and an RAO approved fast start / slow finish with declining rate of rise from start to finish. Great coffee is possible either way. FOR ME an increasing ROR after first crack is where things get roasty and worst case ashy.

    Just to illustrate the differences between the 3 basic style I mentioned, Slow start / fast finish with declining finish, generic straight line profile also with a declining finish and fast start / slow finish RAO rules . These roast are from 3 different origins.

    SSFF.pngStraight.pngFSSF.png
    Last edited by Steve82; 10th August 2016 at 12:18 AM. Reason: Added profile pics

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    Senior Member readeral's Avatar
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    Very helpful! I'll give it all a go. TBH it's a case of getting the best I can from items that honestly aren't made to roast coffee... But that's where most of us are at. I will be modifying that element when I can, and putting a controller on my fan too eventually. All a matter of time.
    The time from 150 to FC has always been the thing that got to me. Never short enough for my liking. It's why I pursued the high preheat in the first place in an effort to reduce the overall time to FC. I'll try ramping my ET from 200 to 250 as you suggest and report back.

    Interestingly, unless I'm careless, I rarely get ashy flavours. Baked however, is probably a feature.

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    Life-long Learner DesigningByCoffee's Avatar
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    Quote Originally Posted by readeral View Post
    Very helpful! I'll give it all a go. TBH it's a case of getting the best I can from items that honestly aren't made to roast coffee... But that's where most of us are at. I will be modifying that element when I can, and putting a controller on my fan too eventually. All a matter of time.
    The time from 150 to FC has always been the thing that got to me. Never short enough for my liking. It's why I pursued the high preheat in the first place in an effort to reduce the overall time to FC. I'll try ramping my ET from 200 to 250 as you suggest and report back.

    Interestingly, unless I'm careless, I rarely get ashy flavours. Baked however, is probably a feature.
    Lots of great advice from Steve

    I would second the ramping advice. Fast start, long slow reducing curve, esp after first crack gives pretty flat flavours in a corretto too.

    As to winter roasting, that does make it hard, depending on how 'wintery' your winters are! The TO is sucking in very cold air, so is bound to be slowing everything down. Case in point was your ethiopian - that seemed very long for that origin?
    I'm not sure how to solve that in a TO. Steve mentioned smaller batches. Or maybe you could use a small blow heater over the top of it so the air it is drawing is warmer? Just thinking leftfield… Some KKTO builders have added a good adjustable heatgun to the system too - that could help with ramping more quickly when required, larger batches or to deal with cold weather. But then again - if you're going to do that, you might as well roast in a corretto!

    Let us know how you get on…
    Matt

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    Senior Member readeral's Avatar
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    Oh, I'm in Sydney Matt. No winteriness compared to your neck of the mountains. I'm just being a wuss.

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    Senior Member readeral's Avatar
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    Also, after pulling the TO apart, there is almost no air transfer from outside the system in. All those vents on the side of the unit are merely for keeping the electronics up top cool. At least that's the case with my Aldi TO. It surprised us when we busted it open for mods, and I've been tempted ever since to put some sort of adjustable vent in the side of my roasting chamber.

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    Senior Member readeral's Avatar
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    And that causes problems for evaporation as it gets pretty humid inside the system without intervention. There's a gap I've put in for my rubber seal which lets enough out during summer, but in winter I've been finding its too much moisture in the hot air. Releasing it needs to be done carefully otherwise the roast runs away. A slower drying phase will definitely help with managing this.

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    Senior Member LeroyC's Avatar
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    Just read through this recent discussion. I have no experience with the KKTO so can't help with specifics, but the thing that sprung to mind when I read your initial post Al was that you need to stretch the drying phase. So I can only echo the sentiments above. I know you like to read and research - have you read the articles on Coffee Shrub about stretching the roast? Could be some good info in there for you.
    So it would depend on the bean, but in your position I'd be wanting to stretch the drying phase then ramp up for a definitive first crack, taking care not to let it get away on you if it's the sort of coffee that has that potential. The other considerations would be air flow and adequate exhaust/venting. Increasing airflow just around first crack would be good if that's possible on your set up.

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    Quote Originally Posted by readeral View Post
    And that causes problems for evaporation as it gets pretty humid inside the system without intervention. There's a gap I've put in for my rubber seal which lets enough out during summer, but in winter I've been finding its too much moisture in the hot air. Releasing it needs to be done carefully otherwise the roast runs away. A slower drying phase will definitely help with managing this.
    This is a pertinent observation. Have a read up on evaporative cooling in regards to " drying stage ". From what you are describing it would be a fair assumption there is lots of it going on. Definitely need to work out some kind of appropriate level of flow IN / OUT through the system.

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    Mal Dimal's Avatar
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    Nothing left for me to say really...
    Steve and Matt have nailed what I would also suggest.
    Let us know how you go Al...

    The intrinsic characteristic of the KKTO to cause an extremely humid roasting environment is one I could never quite overcome and is one of the reasons why I reverted back to a Corretto at the time.

    Even up where we are, some roasts literally caused pools of condensation to collect in the bottom of the roaster because there was just nowhere for it to go; even with a small gap in the top seal... I know this doesn't cause concern for all KKTO operators but it was a limiting factor for me to properly control each roast.

    Mal.

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    Senior Member readeral's Avatar
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    Quote Originally Posted by LeroyC View Post
    Just read through this recent discussion. I have no experience with the KKTO so can't help with specifics, but the thing that sprung to mind when I read your initial post Al was that you need to stretch the drying phase. So I can only echo the sentiments above. I know you like to read and research - have you read the articles on Coffee Shrub about stretching the roast? Could be some good info in there for you.
    So it would depend on the bean, but in your position I'd be wanting to stretch the drying phase then ramp up for a definitive first crack, taking care not to let it get away on you if it's the sort of coffee that has that potential. The other considerations would be air flow and adequate exhaust/venting. Increasing airflow just around first crack would be good if that's possible on your set up.
    The biggest difficulty I've had Leroy is that everything is relative, and so working out what has been subjectively described elsewhere and trying to devise a principle in which to apply to my own system has been very difficult. The advice here however has been very specific and tailored to my questions and concerns which helps me breathe a sigh of relief! Short of working with a consultant, I'd reached the limits of what I could do myself, so all this advice is very welcome.

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    Senior Member readeral's Avatar
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    Quote Originally Posted by Steve82 View Post
    This is a pertinent observation. Have a read up on evaporative cooling in regards to " drying stage ". From what you are describing it would be a fair assumption there is lots of it going on. Definitely need to work out some kind of appropriate level of flow IN / OUT through the system.
    It's _almost_ driving me to use a heat gun instead, just so I can have an opening for exhaust. We'll see what else I can just from this design first.

    The evaporative cooling has been something I've been aware of for a while (ever since I started webering meat) but hadn't resolved yet. I'd been trying to avoid doing much more hole making (cutting this stainless steel really sucked!) but I think that's my only next course of action.

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    Senior Member readeral's Avatar
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    Sorry I've turned this into a "how my roaster operates this week" thread, but hopefully it's a bit of relief for other KKTO owners. I'll report back on Friday or Saturday once I've had a chance to do more batches.

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    Mal Dimal's Avatar
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    I guess you could start up a new thread and ask Javaphile if he wouldn't mind moving the relevant posts into it...

    Mal.

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    Senior Member readeral's Avatar
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    So I gave Steve82's tips a go. Seemed a lot better to me.

    In a whole bunch of ways my profile _looks_ the same as my previously uploaded profiles but with the much lower environment temperature, and a slightly slower drying phase, I've definitely got a bit more aroma and fruity acidity off the freshly roasted beans when I had a munch on one.

    No photos of my roasts. Unfortunately on my first Ethiopian roast my vacuum cleaner suction dropped too much to move the beans (filter problem) so a significant portion of them sat unmoving in the roasting chamber while I sorted it out... but hopefully the slightly burnt surface won't mask the flavour too much and I can make an assessment on how it improved on last weeks efforts. I also did a Rwandan and another Ethiopian with a larger batch size.

    Would love comments and thoughts on this profile of the first Ethiopian batch - 470g.


    One thing I wasn't sure with Steve's recommendation was whether I was ramping right from the turning point onward, or ramping from the end of drying phase. But looking at Matt's profiles and the power levels there, looks like from the get go is what I'm looking for.

    Matt, you suggest that the roast seemed long for the Ethiopian origin - this one is kind of the same. Dropped at 17 minutes, as my ROR was not carrying me any closer to my 218/220 target, due to evaporative cooling I suspect after first crack. However, my first crack still happened at 14 minutes, which was later than I was hoping.

    Still need to work out what is happening with my probe, and why first crack happens at 205 degrees.

    One thing I'm reluctant to do is drop my batch weight any less than 470g of green (that is, 400g of roasted with 15% loss). I roast for mates, and trying to roast ~1.5-2kg of coffee on a Friday arvo when I'm resorting to only putting 400g into the roaster to begin with sounds far too painful to me.

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    Life-long Learner DesigningByCoffee's Avatar
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    Quote Originally Posted by readeral View Post
    Matt, you suggest that the roast seemed long for the Ethiopian origin - this one is kind of the same. Dropped at 17 minutes, as my ROR was not carrying me any closer to my 218/220 target, due to evaporative cooling I suspect after first crack. However, my first crack still happened at 14 minutes, which was later than I was hoping.
    Howdy
    It was more that one of those Ethiopian roasts seemed so much longer than all the other origins. I tend to find that Ethiopians tend to best best when roasted from faster to baseline, then the Brasil/Columbians like baseline–slower. Just comparing all those different profiles
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    Mal Dimal's Avatar
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    Quote Originally Posted by DesigningByCoffee View Post
    the Brasil/Columbians like baseline–slower.
    I usually interpret this as a gentler profile, mainly for lower grown beans...

    Mal.
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    Senior Member readeral's Avatar
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    I'm partly wondering about processing method. A lot of the beans I've struggled with this year have been dry processed beans, rather than wet processed. The bean I've had the most success with was the Mexico El Malinal which is a wet process.

    Can anyone give me insight to my hunch?

    As a result I'm thinking of picking up some Costa Rica Tarrazu San Marcos as my ongoing staple (as there is no more of the Mexico on offer - knew I should've stocked up!). Andy doesn't specify the processing method, but a quick google suggests it is washed. What do you think?

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    Mal Dimal's Avatar
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    G'day Al...

    I don't have any blanket method for roasting either of those processing types as there is quite a lot of variability within each type. There is some info to be found however that may give you some very generalised guidelines to follow, such as this info here...
    Fundamentals - Coffee Roasting - Dry Process vs. Washed Coffees

    Mal.

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    Ok, so I’ve had a munch on some of the Rwandan beans, and there’s a delightful blueberry flavour! I’ve always known these beans could do it, and I’ve never ever got it which has been what’ driving my obsessive change attempts.
    Unfortunately I’ve also detected ashiness and would love some advice on this. My bean mass temp only hit 215 degrees before dropping, and it didn’t get to second crack (nor are the beans oily) so it’s some other thing.
    These beans have never burnt on a preheated system set to 265, so I’m inclined to think that charging at 200 degrees is unlikely to have caused my problem either, but that leaves me a little stumped. I may be wrong on both these thoughts however.


    It’s hard to tell as this is a bit of a mottled bean anyway, but maybe there is some charring in the seam - but it doesn’t look like I have charring throughout the bean. I’m not quite sure what tweak to make to avoid it.


    Here’s the profile I ended up with. It was a 470g green batch, when I’m used to putting 600g green in, so this would likely have played a part as well. With this roast, I couldn’t push it any deeper, even though I was trying to - so didn’t have enough energy into first crack to carry it. I’m playing a balancing game which is proving difficult!

    Rwandan.png

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    Senior Member readeral's Avatar
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    Quote Originally Posted by DesigningByCoffee View Post
    Howdy
    It was more that one of those Ethiopian roasts seemed so much longer than all the other origins. I tend to find that Ethiopians tend to best best when roasted from faster to baseline, then the Brasil/Columbians like baseline–slower. Just comparing all those different profiles
    So if you wanted to roast faster to baseline, there are different variables you could play with: higher preheat, lower batch volume, less development after first crack, higher heat input across the roast.

    My question is, if you were to put these in an order of priority, what would you say?

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    Senior Member readeral's Avatar
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    Ok - my next experiments are to:
    1. Drop my charge temperature to 190
    2. Draw out the drying phase an extra minute, and delay ramping my power levels up until about 1m30s into the roast (rather than right from the get go).
    3. Prop open the roaster slightly (haven't worked this out yet - maybe I'll just make more gaps in my rubber seal) to get more airflow out of the system, and hopefully carrying moisture with it.

    I'm reading from one of Boot's Roast articles that high moisture content requires careful drying phase, and that poor air pressure (and I expect that a closed environment like the KKTO will have quite poor air pressure, even if it has high air speed) will give baked and flattened flavours, and a dulled acidity. Makes sense. It's an oven designed to bake... Can't say that I've always had a dulled acidity in my KKTO roasts as in the past I've dropped quite light, but I can definitely vouch for the baked flavours which I am constantly fighting against.

    The risk of opening up the lip of the roaster is that as the convection air is forced sideways across the face of the glass top, I might just be forcing my hot air out of the roaster from the get go, and lessening what heat energy I have available to actually get my roasts over the first crack line and into proper full development. In the inverse, I'm letting moist air out of the system, avoiding evaporative cooling, and also avoiding a super-hot moist environment damaging the roasting beans.

    I remember reading previously about people modifying the fan blade angles of a TO in order to get more airflow straight down (and actually seeing a subsequent decrease in roast times). This might be something for me to look into doing, but given there was no discussion of roast defects (presence or absence of) with reference to those mods, I'm hesitant.

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    Senior Member readeral's Avatar
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    Also (sorry about the spam) but some of my beans (at least in the Rwandan roast) did bulge open - which I've always known is an indicator of too much heat. My question is - is this too much heat when dropped into the roaster, or is it too much heat in general from the environment, once the drying phase is over?

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    Life-long Learner DesigningByCoffee's Avatar
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    I tend to keep turning point consistent by adjusting my preheat and 'drop zone' gun temp inputs dependent upon ambient and green bean temps. Then increase the ramp from TP to first crack, and leave the post first crack to second crack zone alone unless roasting for filter.

    By your tasting notes, it could be than heat / fan is too hot early on in development. I'd try a slower start (possibly less preheat but certainly post TP heat input) but then increasing higher towards first crack. Beans should be more resilient to higher heat input then

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    Senior Member readeral's Avatar
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    Cool thanks Matt - I just wrote a reply but not sure where it's gone...

    What is 'drop zone'? Re: my turning point, I usually aim for a consistent TP of 80 degrees after 1 minute. My probe is one of Andy's 100mm probes, 3mm wide, so it's pretty quick responding. Alas, I think I've killed it as where FC used to be 200 degrees, it then shifted to 205 degrees, and now it's 206-208 degrees.

    Looking back over Steve's comments, I can see that he was trying to get me to avoid hitting my max ET early in the roast. By ramping right from the start, I still hit my max ET four or so minutes out from first crack. I'm assuming that by delaying my ramp up, I can get better momentum into first crack for a more rigorous crack, as well as avoiding those high environment temperature negatives, damaged beans from earlier high heat input and hopefully carrying it into post-FC development a lot better.

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    Life-long Learner DesigningByCoffee's Avatar
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    I call it the drop zone. I basically preheat the corretto, drop the beans in cold at a certain preheat temp (120-140), and then the zone from load to the TP is the drop zone (sure it has an official name ). I keep the gun running gently at different temps in this zone to get a consistent TP, but at around 40. Seems to work for me

    Could the probe be moving? If you change batch size, you might need to adjust the probe. I have two locations for 350g and 750g batches - get it wrong and it reads 10 out.

    I think your right about ET - lower at the start, hit it harder late. If it is too high early, you're more likely to scorch and tips beans (though I've never experienced this myself!) so might be talking out of my hat!

    Matt
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    Senior Member readeral's Avatar
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    I'm almost at the point of giving up on the KKTO. Almost. Invested hundreds of hours into building the roaster and trying to get a roast that I'm close to satisfied with (granted I'll never be thoroughly satisfied. That's the game of any sort of skill), but I rarely see one!

    I did 4 roasts today to try to nail this slow fast process. I'll upload the graphs of the first 3.. They were "ok". First two roasts were 500 grams and the third was 400g. My last roast I tried 600g which is what I used to do back when I preheated high and left it high, and managed to have the most uneven roast I've had for a long time, with many burnt beans. Needless to say, new approach does not do kindly with larger batches.

    My biggest concern on my first roast was that with an ET of 200 degrees, I wasn't approaching end of drying phase before 8 or so minutes, and so started my ramp before drying was over. I tried ramping over 5 minutes to 255, and eventually pushed it to 265 to try to get a better run up to first crack. It fell short, and in doing so, I then didn't have enough energy to push it through to first crack (206 degrees) let alone much beyond it.

    Rwandan1.png

    In my second roast, I tried an ET preheat of 210, and ramping earlier, letting the machine just ramp as quickly as possible. This was slightly better, and first crack appeared to come earlier (203), but again I had to give it a further boost before first crack and I couldn't get it much past a light roast after backing off from my elevated ET.
    Rwandan2.png
    My third roast I dropped down to 400g (probably the minimum volume I can get away with in this system) to try and give myself access to more energy. I also decided that instead of worrying about what the ET was, I would try to maintain some sort of steady RoR. This was probably the most successful of them all in terms of how dark I could take it - finally an espresso-worthy roast if judging by temperature alone - but first crack came really late (214), and I didn't develop much beyond this temperature.
    Rwandan3.png
    Every roast had some ashy beans.

    I'll cup all the roasts tomorrow, but I doubt any of them will have that fruity acidity I had last week. What a depressing day of roasting.

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    I have no experience with the KKTO but have used two different drum roasters, so apologies for the really basic questions. First question is why 400 g is the smallest charge you can use? When I was reading about your problems it immediately sounded like they should be fixable by lowering charge weight. The very slow move to dry (I consider 6 minutes as slow as I'd want and with smaller charges I get there in 4 minutes) and the inability to get the system temp through first crack and beyond sound exactly like charge weight is too high.

  32. #32
    Senior Member readeral's Avatar
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    Probably could go less, but general convention in previous threads suggests 400g is the lower range for proper bean agitation and avoiding scorching the beans.

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    Oh, and very sorry to hear you describe your "depressing day of roasting ". We've all been there! I've produced kilos of ash.

  34. #34
    Senior Member readeral's Avatar
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    Previously my drying was only 5 or so minutes, but that's with a preheat of 265 degrees. The suggestion above was that my drying was (proportionally) too fast then. It just doesn't seem I can get much momentum in this roaster without terribly high temperatures. Probably cause it does such a good job of distributing that heat evenly throughout the system. Maybe I'll dare to tweak how the fan works to get more direct heat onto my beans.

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    So the problem is that despite getting ET close to the limit (I find that ET greater than about 270 C causes ashiness and scorching) that you still can't get enough energy into the system. How is airflow controlled in a KKTO? If I had the same problems on a drum roaster I'd increase airflow and raise gas to get same ET but higher system energy.

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    You beat me to it. 265 preheat is incredible to me. Again using a drum I preheat to about 180 and even lower when I'm roasting for pour over.

  37. #37
    Senior Member readeral's Avatar
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    Quote Originally Posted by kwantfm View Post
    So the problem is that despite getting ET close to the limit (I find that ET greater than about 270 C causes ashiness and scorching) that you still can't get enough energy into the system. How is airflow controlled in a KKTO? If I had the same problems on a drum roaster I'd increase airflow and raise gas to get same ET but higher system energy.
    So there's just a central fan that sits above the whole system, not behind the heat source, but "inside" it (hard to describe) pushing it out to the perimeter of the chamber and circling it round. It's indirect, so ultimately probably terrible airflow in traditional terms. I've been convinced for some time that the airflow is significantly ineffective.

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    Will be very interested to see whether your fan tweaking experiments yield results. Good luck!
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  39. #39
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    I think I'll be looking at converting this into a "glorified breadmaker" and go with a heat gun, and ditch my electronic control via my roasting software. I suspect it's the only way I'm going to get the kind of airflow that I really want. Just a bummer that so many seemed satisfied with the KKTO over the years. Maybe I have much higher expectations!

  40. #40
    Senior Member readeral's Avatar
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    Quote Originally Posted by kwantfm View Post
    Will be very interested to see whether your fan tweaking experiments yield results. Good luck!
    Thanks! I'll give it a go.

  41. #41
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    Quote Originally Posted by kwantfm View Post
    So the problem is that despite getting ET close to the limit (I find that ET greater than about 270 C causes ashiness and scorching) that you still can't get enough energy into the system. How is airflow controlled in a KKTO? If I had the same problems on a drum roaster I'd increase airflow and raise gas to get same ET but higher system energy.
    Also I may use "ET" incorrectly, as I'm referring to the general environment temperature, rather than an exhaust temp. That's the other downside with this whole setup is not being able to create negative air pressure with an exhaust to draw the hot air through. It (generally) is fairly static air. The definition of baking. Given turbo ovens are... ovens... that's what it's really designed to do!

  42. #42
    Senior Member Yelta's Avatar
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    Quote Originally Posted by readeral View Post
    I think I'll be looking at converting this into a "glorified breadmaker" and go with a heat gun, and ditch my electronic control via my roasting software. I suspect it's the only way I'm going to get the kind of airflow that I really want. Just a bummer that so many seemed satisfied with the KKTO over the years. Maybe I have much higher expectations!
    Have never used a KKTO so cant comment on the device, however I have been using a Coretto for over 10 years with great success, my setup really is quite basic, Breville single loaf bread maker, Bosch variable speed heat gun, DMM with temp probe and timing with wrist watch.

    I roast 725 grams weekly, over cooked one batch slightly in the early days, since then have not had a failure, perhaps I'm not as fussy or as scientific as some, however i do know and enjoy good coffee and consider my efforts as well above average.

    The one disadvantage with a Coretto is uncontrolled chaff, I'm sure this could be controlled, not a problem for me as I roast in a shed and set up a pedestal fan to blow the chaff into the garden.

    Not attempting to denigrate the KKTO, simply explaining a setup that works very well for me.
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    Quote Originally Posted by readeral View Post
    I'm assuming that by delaying my ramp up, I can get better momentum into first crack for a more rigorous crack, as well as avoiding those high environment temperature negatives, damaged beans from earlier high heat input and hopefully carrying it into post-FC development a lot better.
    There are some interesting observations in this thread, and clearly a lot of collective roasting experience, but there also appear to be some misconceptions about the fundamentals of heat transfer.

    Forget about 'momentum' - it's a misleading analogy. What you are describing is a product of the temperature gradient in the bean (i.e. that the middle of the bean is at a lower temperature that the outer surface).

    If you start with a cold bean and pass hot air over it, heat (energy) is transferred from the air to the bean surface. The rate of convective heat transfer depends primarily on the difference in temperature between the air and the bean, and on the velocity of the air.

    Meanwhile, heat is being conducted away from the surface of the bean towards the centre. It takes time for this to happen (and from memory the dynamics are primarily a function of conductivity and heat capacity).

    If conduction through the bean is rapid relative to convection then there won't be a significant temperature gradient (i.e. if heat is transferred away from the surface nearly as fast as is is transferred to it, then the temperature at the inside of the bean will be close to that of the surface).

    If, on the other hand, the rate of convection is very high relative to conduction (through the bean) then the surface temperature will rise faster than the centre temperature (resulting in a temperature gradient).

    This effect is amplified when the air temperature is increasing (because the surface temperature will rise with it faster than the centre).

    Now, first crack occurs once a particular temperature is reached. The slower the temperature rise of the bean surface in the lead up to FC, the closer the centre of the bean will be to FC temperature - perhaps resulting in the observed "tighter" first crack.

    This of course is somewhat simplified - chemical reactions and physical changes in the bean as it expands complicate the situation beyond simple heat transfer - but it is still useful for picturing what is happening.


    A picture is worth a thousand words: https://youtu.be/NwpJDV5vzm8
    Last edited by MrJack; 20th August 2016 at 02:21 AM.
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  44. #44
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    MrJack, most of this I understood from many sources I've read, thanks for a concise summary. I might be using the term 'momentum' unhelpfully, but I suppose I have meant 'ongoing heat transfer' especially as the roast has progressed. It's a minor point in a broader discussion that essentially is determining: 'effective heat transfer to the bean, and through the bean is essential' and as the whole roast is progressing very slowly, due to poor transfer, the beans are subject to high temperature for a long time. Couple this with the likely evaporative cooling due to poor exhaust/air flow, and we've got ourselves a complex problem.

    The salient comment you made is "The rate of convective heat transfer depends primarily on the difference in temperature between the air and the bean, and on the velocity of the air." What I'm finding is that although this is a 'convection oven' unit, I'm getting very little convective transfer of heat given how it's now being used. The challenge I'm trying to solve is how to improve energy transfer to and through the bean for a successful roast within reasonable parameters. The success of the suggestion by kwantfm of lowering the batch is contingent on good roaster design to have good, direct convection (and, lesser so conduction/radiation), which I personally feel it does not have. I obviously have no instruments to actually measure this, and chaff flying around the roaster seems to contradict my hunch, but I think the problem may lie in the issue of air pressure (which, if I have understood correctly, means with negative pressure outside the system will produce air flow through the roaster) - rather than just air movement.

    The reason - I suspect, and honestly all of this is just hunch given I am a musician not an engineer - that lowering the batch will not help much anyway is that: given the size of the roaster, the amount of energy lost to the increasingly exposed metal surfaces of the roaster (to be conducted outward to the ambient air), will offset the desired gains from a lower batch size. Creating better convection directly to the beans, rather than to the surfaces of the roaster, should help a lot more.

    I'm sure I've got some science wrong - feel free to correct me, but in the context of solving this problem of effectively executing a slow-fast profile in a KKTO.
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  45. #45
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    I think the profile you are trying to achieve is not particularly suited to the KKTO, all my profiles have a slightly decreasing RoR to FC, it starts around 11deg/m and at first crack is around 6.5deg/m, then I continue to control a slowly falling RoR from FC to SC - from 6.5deg/m down to around 3.5deg/m at the end of the roast. I aim for a Rao style profile with 20-25% of the time to FC for the phase between FC & finishing.

    I roast 1.2kg batches in my KKTO, i bypass the thermo couple so the heat is always on, i lift the TO off to 'burp' when I need to control RoR.

    I actually found over the years that bigger batches are easier to manage in the KKTO - as long as you bypass the cycling of the element.

    Temps and thermocouples are something I use relatively - they do vary and its more important to observe whats happening (FC, SC, etc) than relying on what you think should be happening at a given temp. Different beans vary a lot too. I dont bother any more with ET, I think its more important in drum type roasters, I couldnt find any correlation in the KKTO.

    My load temp is 250 deg.
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  46. #46
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    Hi ArnhemR - it's not suited to the KKTO, you're right, but alas I own a KKTO and it's coffee is not suited to my tastes! So I'm seeing what I can do to modify the design or approach to make it do what I want. One day I'll fail in this pursuit and get a more suitable roaster for my liking :P But in the meantime I'm a student, living in an apartment, with no income of my own so... this is the extent to which my wife will let me go. All I want is those delicious fruity flavours that I know exist in my (especially African) greens. But maybe I'll have to stick to nuttiness and cocoa.

    My turbo oven already has (almost) as much control of it as I can wield. I can already control it's power level (albeit through pulsing rather than PWM) from always on through to always off. Rather than let it go full boar, I usually use my PID to set a maximum environment temperature. This isn't ideal, as really I should have the thing on full boar most of the time, and have some way of controlling the airflow to manipulate my environment temps. Corretto owners do this with lids on their bread pans, KKTO owners like yourself typically do it with burping. I found that KKTO approach too difficult to repeat but maybe I should give it another shot.

    I'm well aware that my thermocouples will behave uniquely - most of the concern about TCs in this thread is that they have drifted, so what value they have had recently is diminishing - until I fix the problem. Whether I like it or not, TCs are my best guide with my KKTO. With a small bean mass and a large amount of mechanical noise (don't know about you, but my Turbo Oven has got to the stage of rattling and requires retightening regularly) first crack isn't very discernable, and telling steam and smoke apart with such a sealed system is difficult.

    Most of the people I have read that are happy with KKTOs are, like yourself, much further north than I am. Makes me wonder whether there is a distinct advantage for the KKTO user in a warmer ambient climate. I had much less finicky roasts in summer (Again well aware that all roasters require adjustments for winter conditions).

    On the design front, I would posit that a solution would be to actually build in an exhaust (with fan). Either a tube straight down from false floor through the base, or diagonally from false floor to wall of roaster - which will draw the warm convective air across the beans with much more velocity, pull out chaff, draw out steam and smoke and make airflow a controllable dimension of the roast without more mods to my Turbo Oven. Then I could have the turbo oven always on. But the idea of more Stainless Steel drilling is not at all appealing, and further engineering decisions like diameter of tubes would make it a risky move. Still - I might do that some time as an experiment.

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    fair points readeral, you are aiming for the opposite flavour profile to my preference so i dont have anything to offer you there!

    I am surprised you cant hear FC clearly - thats never been an issue with my KKTO

    I sort of get the feeling though that you are complicating the process somewhat, I have never felt that controlling the air low was necessary, although I did experiment with a speed controller on the fan but found I couldnt detect any difference.

    I do think bigger batches are easier to control on the KKTO, I would suggest you try the biggest batch that makes sense with your usage. If you can roast as much as 600g green, aiming for 500g roasted (roughly), then I would try preheating to around 180deg and drop in the beans and leave on full heat until just before FC, start burping to slow the BT RoR to around 5 deg/m and finish when you like the look of the beans. Alternatively control the RoR approaching FC by turning the thermostat right down.

    What software are you using to record profiles?

    I would be surprised if it were not possible to roast on the KKTO to suit your flavour profile without major mods.

    Its worth hitting up Paul (the inventor of the KKTO ) for his thoughts, he is always happy to share his vast knowledge and experience.
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  48. #48
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    Quote Originally Posted by readeral View Post
    Couple this with the likely evaporative cooling due to poor exhaust/air flow, and we've got ourselves a complex problem.

    I'm sure I've got some science wrong - feel free to correct me, but in the context of solving this problem of effectively executing a slow-fast profile in a KKTO.
    I'll return to the rest of you post a bit later when not on my phone, but I just wanted to ask - where the evaporative cooling concerns have come from? i.e. what do you think is going on, and why do you think it is of particular concern in your roaster?

  49. #49
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    Hello again Al...

    An Aussie source of some really good info about coffee roasting comes from highly respected Roaster Extraordinaire Anne Cooper, who currently has been running a series of articles in the Cafe Culture Magazine. All of their articles can be read online or the magazine can be subscribed.

    Anyway, thought that this episode might have some information of interest for you, starting on page #32...
    https://issuu.com/cafeculture/docs/c...22766/37516812

    Mal.

  50. #50
    Senior Member readeral's Avatar
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    Behmor Coffee Roaster
    Excellent, thanks Mal. Glad she's been writing - a mate of mine went on some workshops with her and thought she was brilliant (I actually have a copy of that equilibrium graph on my PC - but not with her heat transfer details). Alas, a lot of what he took away (beyond this excellent kind of content), was specific to his Has Garanti.

    It's good to read the distinction of natural and forced convection, and how it needs to carry the bulk of the roast. Gives me confidence in the lower charge temps, but also my need for improved convection.
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