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CharcoalRoaster
11/04/2019 1:58 AM
+1 snwcmpr

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11/03/2019 2:16 AM
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allenb
11/01/2019 2:20 AM
Funopt, please post in the gas and electric heat sources forum

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10/30/2019 5:17 AM
Can someone help me for using forced propane burner as my heating element. I rather want to use lpg than electric. Do you think it would work

snwcmpr
10/22/2019 5:31 AM
Thanks to you all....... I was not sleeping ... I stayed awake worried about it all. :)

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endothermic reversal point
JETROASTER
Dan wrote:
Yes, steam is releasing heat since it is hotter than the environment, and it does tend to remove heat from the bean, making it an exothermic process, but it is not an exothermic CHEMICAL REACTION since the water/steam started and ended as H2O. That is there was no chemical reaction, just simple heating and cooling.



That sounds like a good fit for 1C. Then the exotherm at 2C must be
getting close to combusting on its own? -Scott
 
Dan
Based on my experience, roasts go exothermic right about 2nd crack. On some of my darker roasts (FC+ to Vienna) I turn the heater off when 2nd crack gets rolling. I've noticed that the thermocouple in the bean mass measures a temperature rise even though the heater is off, a sure indication of an exothermic reaction going on.

In commercial roasting circles they talk about the dreaded "3rd crack." A roast that is so violently exothermic that heat builds to where you see flames.
 
http://www.intactamerica.org
JETROASTER
"3rd crack" is followed by "1st fire bottle". Been there.

Although it may not be a true exotherm, the heat/steam
release around 1st C still interests me.
It ties in with the thread about 'monitoring moisture during roast' as well as 'regarding the pre-yellow stage'

If all of this makes no sense, I apologize in advance.

Depending on how pronounced that reversal/release is,(around 1st C) it would seem a strong indicator as to whether or not you entered the roast as you intended.

....But how would you measure it? It seems that the thermometer doesn't tell the whole story during that part of the roast. The moisture release clouds the picture.

Is there a good way to measure humidity within the RC of an air-roaster ? -Scott

 
eric
Nice summary Wallace. I have about as many roasts under the belt as you, all with air roasters. I am more with Ed on the science - though there is plenty of art in getting crude consumer roasters to perform! Coffee roasting definitely qualifies as a chaotic process, which is what makes it so difficult to control. Later stages are very dependent upon earlier for their results. Whole chemical reaction pathways may be cut off by how the roast is set up in its earlier stages: amount of drying affects reaction pathways later in the roast due to residual water availability. RoR will affect vapor pressure within the bean and guide pathways as well. Fiendishly complex. IMHO.

I will take exception to one of your statements - the folklore around exothermic reactions at 1C - I am sure there is no such thing. I have never seen it with my setups that should have shown it: very low thermal mass air roasters with good thermometry can easily detect any exothermic reaction as a rise of bean temp above env temp. Never happens, even on quite low RoR through 1st. There is sometimes a very marked reduction in apparent thermal capacity after what I call the Maillard hump before 1st and if your roaster has any sort of thermal delay between power and BT then you could be fooled into thinking things were getting exo into 1st. The Maillard reactions can be very endothermic (hump usually around BT 180-185C for me). No-one mentions it, but the max RoR through this phase at a given batch size is an important spec for a roaster and where I will hit the power limit first for profiles that I prefer.

On the title of this thread, getting through Maillard as quickly as possible will minimise the sugars consumption of the Maillard reactions and leave them for caramellisation later in the roast. ThumbsUp

My 2c...
Eric
 
Dan
This might help. Raemy and Lambelet measured coffee energies in their study and found that roasting becomes markedly exothermic around 195°F. as seen in this graph.
Dan attached the following image:
raemy_lambelet_1.jpg

1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
Ringo
The way I understand it is when the beans go through 1st crack steam is released causing the heat to rise. On my drum roaster when 1st crack starts I have to cut way back on the heat but as 1st crack winds down I have to add heat so the roast does not stall. I would guess you would not see this rise in a air roaster because the steam would be blown out the top, but in a drum the beans are rolling in a pile.
All you need in life is ignorance and confidence, and then success is sure. Mark Twain
 
Dan
Actually, releasing steam COOLS the beans! Steam is heat leaving the bean. What you might see happening is the beginning of the Maillard reaction. As moisture leaves, the bean becomes dryer, and sugars can begin to brown, this stage is slightly exothermic. You can see that in the graph above. The 45° slope from 170°F to 190°F is the sugars being browned. The steeper portion are from the remaining hydrocarbons.
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
JETROASTER
It seems like perhaps the endothermic/exothermic discussion is out there again, I figured I'd put this thread back up to keep things tidy.

Here's a question. I don't believe I'm ever reading actual bean-temp....and i could be wrong. It seems it's always some form of enviromental reading.
If that is true, how can anyone be sure of what the beans are doing?
-Scott
 
Dan
What food scientists do is a calorific test in a calorimeter. We did them in high school chemistry. You put a small sample in a sealed container, heat it up and measure any change in heat. That's what the Raemy and Lambelet graph I often post is from. Using this test you eliminate any environmental causes such as heating the drum, cooling from a breeze, etc. What R&L did was grind some green beans, steep in water to pull out anything soluble in water, and then test the coffee-water and spent grounds separately in a calorimeter. Here are those two overlaid on the same graph.
Dan attached the following image:
raemy_lambelet_2.jpg

1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
JETROASTER
....so, I understand this to be proof that it is releasing its own energy at that point?
(When I first started roasting, I had a little book from M Sivetz that spoke of this, I really just took it as gospel.)
But....there are some opposing views out there.
I believe the other point of view is that coffee isn't releasing energy unless it's on fire?
I'd like to hear that as well.

-Scott
 
Dan
Scott, I know there's been a lot of talk about this on this forum and other forums over the years, but I thought by now everyone had come to understand the simple science of the Maillard reaction. Yes, these graphs are scientific proof of an exothermic reaction. Here is the abstract for that article which clearly states coffee roasting is exothermic and even warns that it is so intense that it can start a fire:

"The technique of heat flow calorimetry was used to determine the specific heat of coffee and chicory products and to study their thermal behaviour above 20°C. Intensive exothermic reactions were particularly evident when measurements were made with sealed cells. The data obtained help in the understanding of how exothermic reactions (and self-heating) occurring in such foodstuffs can bring them above their minimum ignition temperature."*

The notion that roasting coffee is not exothermic is a falsehood. Granted, there are roasters who disagree, but until they run their own calorific tests and get it published in a peer-review journal, I'm going to stick with what these two dudes are saying.

Burning hydrocarbons are indeed releasing energy and it is therefore an exothermic reaction, but then so is mixing a two-part epoxy. If you've ever mixed too much in a paper cup you know it gets warm. That's an exothermic reaction, too.

*Raemy A, Lambelet P. A calorimetric study of self-heating in coffee and chicory. Int J Food Sci & Tech, 1982;17(4):451–460.
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
Ringo
ok This will be my last post on this subject. The old timer that showed my how to roast explained that coffee takes in heat until 1st crack were it gives up heat. Its not a chemical reaction its heat stored in the steam. He did use the words endothermic an exothermic but only to mean the take in heat or release heat. When steam is no longer under pressure it releases heat, the higher the steam pressure is the more heat that is stored. In some roasters the release of steam will raise the environmental temp of the roast for a short time. I really never understood that the discussion on this was weather there was a chemical reaction because I agree there is no way there is a chemical reaction. I work with boilers in my day job that are used for industrial heating and I do think there is "stored" heat in steam. When I roast on my behmor of my IRoast2 i do not see this heat release, I think the heat is released with the steam its just the roaster is too open and the heat dissipates. If you roast someday on a commercial drum roaster I believe you will see this need to cut the heat at 1st crack. I am probably not right on the reason this happens but in a drum the roast will steed up if you do not cut the BTU's. On somethings we will not always agree and that ok.
All you need in life is ignorance and confidence, and then success is sure. Mark Twain
 
Dan
Ringo, A drum is a more or less sealed container. When water is heated and leaves the beans for the drum the amount of heat the beans lose is exactly the same as what the drum gains. In other words, the amount of heat stays the same.

Maybe I'm missing something, but this sounds a lot like the old "overloaded semi-trailer full of pidgeons on the weigh scale story." As the story goes, the driver bangs on the truck, the pidgeons fly, and presumably he passes the weigh limit. Keep in mind that MythBusters busted this very convincingly. Maybe we should ask them to test this "myth," too. :)
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
JETROASTER
Scientific data aside, it sounds like it matters to the drum folks. The transition is something that has to be anticipated or bad things happen.

What about for the air-roaster? Do I care? Would there be an advantage for me if I could pinpoint the moment of transition?
-Scott
 
ginny
The notion that roasting coffee is not exothermic is a falsehood. Granted, there are roasters who disagree, but until they run their own calorific tests and get it published in a peer-review journal, I'm going to stick with what these two dudes are saying.


well Dan, you can stick with those two guys. many more do not agree.

there is only one thing I can think of you get with an "overloaded semi-trailer full of pidgeons."

ginny
 
Dan
Oh, I'm not asking for anyone to agree with me, Ginny. I'm just sharing what I've learned and talking about what works for Dan.
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
boar_d_laze
Dan wrote: becomes markedly exothermic around 195°F. as seen in this graph.


195C not F. It's probably just a typo, but you repeated it in your next post. Worth correcting in case a newbie is lurking.

Finally:
Actually, releasing steam COOLS the beans!
No.

Setting aside the question of whether the reactions occurring in the beans are endothermic or exothermic -- the beans continue to gain heat if for no other reason than because the environmental temperature is higher than the bean temperature and the ordinary laws of thermodynamics apply.

BDL
USRC 1lb Roaster, Chemex+Kone, Espro, Various FPs, Royal Siphon Vacuum, Yama Ice Drip Tower, Bunnzilla, La Cimbali M21 Casa, Ceado E92.
CookFoodGood
 
Dan
BDL, Thanks for the temperature correction. Right, heat moves from hot to cold. And, speaking of the laws of thermodynamics, changing liquid to gas (water to steam) requires heat. When that steam leaves the bean that bean now contains less heat than before. Same basic principle as a swamp cooler.

Dan
1 pound electric sample roaster, 3 pound direct-flame roaster, both handmade; modified Mazzer Mini grinder, LaSpaziale Vivaldi II automatic espresso machine. When the electricity goes out I make vacpot coffee from beans ground on my Zassenhaus hand grinder, and heat the water with a teakettle on the gas range.
 
http://www.intactamerica.org
boar_d_laze
Dan,

With respect:

Steam leaving the beans doesn't mean the beans are losing net temp or net heat energy for that matter -- it means they're losing moisture.

You already said the beans were in the midst of an exothermia. That means their generating their own heat energy. They can't be exothermic and cooling at the same time. Being a net emitter of energy or steam isn't the same thing as cooling.

The little study you got that graph from says exothermia occurs as well.

As long as ET is greater than BT, losing steam at 1st C doesn't "cool the beans." It can mean a lot of things, but with roaster heat and fan constant, BT measurements prove that BT doesn't drop at first crack. They actually show an increase in BT rate of rise. ET RoR, too.

If you're saying that the beans would be even hotter; and/or have a faster temp rate of rise; and or emit more energy if they didn't give off steam, those are different inquiries.

The swamp cooler model is largely inapplicable. As their is no external heat source other than ambient air temp, and the water inside isn't filled with objects in the midst of pyrolysis.

Considering that this is the internet and that I'm new on this forum it probably needs saying that I'm not trying to show you up -- just help you out.

BDL
USRC 1lb Roaster, Chemex+Kone, Espro, Various FPs, Royal Siphon Vacuum, Yama Ice Drip Tower, Bunnzilla, La Cimbali M21 Casa, Ceado E92.
CookFoodGood
 
boar_d_laze
eric wrote:



I will take exception to one of your statements - the folklore around exothermic reactions at 1C - I am sure there is no such thing. I have never seen it with my setups that should have shown it: very low thermal mass air roasters with good thermometry can easily detect any exothermic reaction as a rise of bean temp above env temp.


Bad hypothesis. Exothermia doesn't mean that BT would be greater than ET. Exothermia would mean a faster rate of rise for BT AND ET (because the beans would be heating the environment by being net emitters of energy) than would otherwise occur absent exothermia.

The hallmark of science isn't making or using measurements which can be expressed with numbers, it's "scientific method" which is just a way of thinking things through and testing the guesses.

BDL
USRC 1lb Roaster, Chemex+Kone, Espro, Various FPs, Royal Siphon Vacuum, Yama Ice Drip Tower, Bunnzilla, La Cimbali M21 Casa, Ceado E92.
CookFoodGood
 
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