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How far into second crack, if at all?
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Frost
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Frost
Joined: 26 Jul 2007
Posts: 2,099
Location: Sierra
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Posted Sat Feb 8, 2014, 10:41am
Subject: Re: How far into second crack, if at all?
 

boar_d_laze Said:

That didn't take long. So much for good intentions. Why do I let myself get roped in?
OK.  It's a made up term which you used without defining in hopes of improving communication.  Whatever you meant by it then and now (still not entirely clear) it has little do with efficiency, or transferring heat.  

While I'm familiar with the term "phase lag" in a few contexts, I'm not sure what you mean by it here.  

Maybe I'm wrong about this -- I hope I am -- but technical terms strewn about like confetti without their "term of art" meanings, is often indicia that the author is trying to sound more knowledgeable than (s)he actually is.  

How could you possibly know what I "might think" about ratios?  I haven't said a word except about skillets and popcorn roasters.  You're probably thinking of the guy who ghost writes for Karl Schmidt, President, Probat Inc.

I'm not sure whether or not "component" is the right word insofar as agitation relates to transfer.  I think it's more about how evenly the heat is transferred throughout the mass.  But it's close enough for me to at least understand what you mean by it.  But there's something I don't get... What's your point?  Just musing?  Or, does "agitation" relate to the usefulness of ET's importance as an indicator of what's happening to the beans through every phase of the roast in some non-obvious way.    

Better roasters do offer better control than worser roasters; one thing which makes them better.  

Bigger machines are not necessarily better.  And -- just speaking generally -- at a certain level of capacity you lose a great deal control to the thermal momentum of the bean mass, the roaster mass, limitations on how much heat you can actually pump into a roaster (no matter how it's pumped) without damaging the roast, and surface area-volume considerations.  

That's partly why even high volume artisanal roasters add mid-sized roasters to meet supply, rather than investing in a big boy.      

If you're saying roasting a large charge requires a roaster large enough to handle it; you're not adding much to the conversation but you're right.    

Yes.

I not only have, but have discussed it in some detail in several posts within this thread.

That takes nerve.  

You don't have even a shred of an idea where my ET probe is located.  The only problem with the its location and the accuracy of the information provided is that it doesn't fit your idea of good information.  It not only works for me, but works for the people doing the roasting in the world-class shop where I trained under one of the best roasters in the country.

Or -- second possibility here -- you're wrong and the beans take energy from another source besides hot air.  

BDL

Posted February 5, 2014 link


I have never witnessed such a display of surly arrogance and ignorance here. Normally I don't respond to such and let it stand on it's merit, but it is also a direct assault on my integrity. (as well as Probat Burns)

I try to be concise and clear, using as few words as possible, when posting on forums.
I do know what I'm talking about, but this thread has been poisoned for further productive discussion.

'Heat Transfer Efficiency' is a 'made up term' but I can't take credit for making it up. It is commonly used in describing heat exchangers. It is obvious the ways a coffee roaster can be characterized as a heat exchanger.

Phase Lag or Phase Shift, (in this context maybe it would be easier to call it 'thermal lag', but then just more 'word salad'.) is germane to the subject and in particular what you are seeing in your roaster ET/BT profile.

Your ET probe location in the exhaust stream is meaningful, but what you are observing points to problems and ways you may be able to improve control of your roast profile.

The convection/conduction ratio is important for roasters. Air roasters always have too much and drum roasters can never have too much.  Ideally, you want a knob that can control it at least to some degree.

My background includes 22 years developing automated semiconductor manufacturing process control systems for Lam Research. (more word salad)
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boar_d_laze
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Posted Sat Feb 8, 2014, 12:44pm
Subject: Re: How far into second crack, if at all?
 

I owe whomever wrote the Probat Burns article an apology.  I misread the article and missed a comma.  My reading that energy sources were limited to convection and bean to bean contact was mistaken; other contact conduction was clearly included.  That aside, I stand by my comment regarding perforated drums and radiant energy.

Frost, I don't care what you did for Lam, how smart you are, nor how much you know about any of a variety of topics.  They have nothing to do with roasting coffee.  You're not the only person with a technical background or education.  For the little it's worth, I have some of both and neither helps me much with roasting.  

Regarding the question/challenge as to how I'd calculate ratio, I'd use Rayleigh's Number.  No.  I didn't look it up in Wikipedia.  

If I didn't feel compelled to acknowledge my error regarding the Probat Burns article, I wouldn't have added to this long, sad mess.  But with that out of the way, that's it.  I'm done.

May all your roasts be delicious,
BDL
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Frost
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Frost
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Posted Sat Feb 8, 2014, 1:21pm
Subject: Re: How far into second crack, if at all?
 

I've been home roasting my own coffee since 1984.  Understanding your roaster can't hurt, and can only help your roast quality.

Edit; And no, I wasn't expecting an apology.
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Frost
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Frost
Joined: 26 Jul 2007
Posts: 2,099
Location: Sierra
Expertise: I love coffee

Espresso: Isomac Venus
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Posted Mon Feb 10, 2014, 7:34pm
Subject: Re: How far into second crack, if at all?
 

Frost Said:

............
Also the Behmor is a unique case as it uses a radiant element; I have no idea where it operates.

Posted February 4, 2014 link


I wanted to pull this out of the weeds to better clarify what I meant to say.

The Behmor uses a quartz heater and the 'drum' is a wire mesh 'basket', fairly transparent to allow direct radiant heating of the beans. The oven walls are reflective as well. Contrast this with the Hottop that uses a cal rod heater that operates at lower temperatures and uses a perforated drum allowing much less direct radiant heat of lower intensity to reach the beans directly.

(If anyone has actual numbers on any of these roasters, approximate ratios of convection/radiant/conduction; please most welcome to provide data.)

Radiant heat travels 'line of sight' (same as light), so will heat the bean mass more evenly and efficiently than conduction that occurs only at point of contact, but it will not penetrate into the bean mass like forced convection. Only the beans in line with the heating element are heated. The other beans in the drum wait their turn as they tumble through the drum.

Obviously the air in the Behmor oven is heated as well by the element,  but the amount of direct radiant heat to the beans is uniquely higher than other roasters.   How much radiant heat as percentage? I don't know.

Darker colored objects will absorb more radiant heat than lighter colors. This is working somewhat against you with coffee roasting as the lighter green to yellow to tan phase of the bean (when you need to put the most heat into the bean) will absorb less radiant heat. During the finish, the bean is darkest and absorbing more radiant heat, and also more porous/less conductive, delicate, and the phase where the least amount of added heat is needed. Be careful about damaging the bean with too much heat now; Here is where you really want to back off the radiant heat intensity.  I know many suggest cracking the door open during this phase to slow the roast, but this doesn't really accomplish the same thing (...with the heater still full on). You are increasing the temperature gradient across the bean mass when you ideally want to minimise it. Also you risk stalling the finish by introducing cold air into the oven and breaking an important rule about roasting coffee;

File it under coffee roasting general principles, regardless if you are using a dog bowl or a shop roaster:

  • You never want to allow the beans to loose heat during the roast. Strive to minimise or eliminate this possibility. This is most important during the later stages of the roast when the roast reactions are occuring. Keep the roast moving forward at all times.

The only time you want the bean mass to loose heat is when you dump them to cool.
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Frost
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Frost
Joined: 26 Jul 2007
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Location: Sierra
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Espresso: Isomac Venus
Grinder: Lelit PL53
Roaster: Poppery I w/variac, MET, BT
Posted Wed Feb 12, 2014, 10:34am
Subject: Re: How far into second crack, if at all?
 

Cleaning out old dead links I came across this excellent reference by Carl Staub;
(Thank you Sweet Maria's for this and not breaking links)

http://www.sweetmarias.com/roast.carlstaub.html

It is packed with good information, temperatures,  what happens when during the roast, why you want to avoid a hot drum/cool air finish, and OMG! he used the term 'System Transfer Efficiency' (STE). Time to update my vocabulary.

This article also reminded me of another sign you have crossed into dark roast territory. (in addition to entry into second crack) The amount of surface oil on the bean(s) is an indicator the beans have been exposed to higher temperatures during the roast . After 7-10 days rest, I expect a Full City roast to appear dry, no sheen, no surface oil.  A few pops of second crack, Full City+ I will sometimes see tiny spots of oil on some beans after 7 days rest.

Getting more surface oil earlier in the roast is an indication of higher ET temps during the roast.
Edit: more careful/accurate wording; it is an indication the bean has reached higher temperatures during the roast.
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CraigA
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CraigA
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Posted Wed Feb 12, 2014, 11:28am
Subject: Re: How far into second crack, if at all?
 

Frost Said:

Cleaning out old dead links I came across this excellent reference by Carl Staub;
(Thank you Sweet Maria's for this and not breaking links)

http://www.sweetmarias.com/roast.carlstaub.html

It is packed with good information, temperatures,  what happens when during the roast, why you want to avoid a hot drum/cool air finish, and OMG! he used the term 'System Transfer Efficiency' (STE). Time to update my vocabulary.

Posted February 12, 2014 link

+1  Gary!! , I love that reference by Carl Staub! {;-)

 
http://twitter.com/CoffeegeekCraig
http://www.facebook.com/craig.andrews.169

Excellent coffee doesn't just happen!
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