deidrichizing, now more cerebrally
September 14, 2007 – 1:18 amwarning: wee-hour wonkiness follows.
casting about the interconnected webs for some sort of roasting standard whereby one can be sure he is “properly drying” coffee without baking them thar beayns, we stubbed our shins on a handy reminder that the audible first crack in the roast process is an exothermic reaction, meaning th’ beayns generate heat themselves, thus adding to the temperature in the roast chamber.
very quickly thereafter, they revert to the endothermic status of absorbing heat, which is a crucial time to make sure enough outside heat is being applied to avoid stalling the roast. (jaime offers a parallel text). it would seem to this blog that even with a finely tailored air-roast profile, ambient temperatures could easily alter when this switch takes place during a given roast. all the more reason to hover, then, and manipulate the airflow as needed to avoid temperature plateaus.
we’re calling our solution the finger’s lid juggle!
ultimately, “baking” would appear to occur any time temperatures flatline after beans begin to caramelize — or sucrose begins to melt. gurus having been consulted, that benchmark would appear to be roughly 370 degrees.
bonus inquiry: if, as our lady of wikipedia observes, an example of exothermy is “mixing water and strong acids,” then wouldn’t that sort of qualify coffee brewing itself? a gin and tonic with lime? just asking!
10 Responses to “deidrichizing, now more cerebrally”
Small tidbits of wisdom that I learned the hard way:
- Try not to roast any fresh crop/WP coffee on a rainy/humid day. If you must, choose DP or (god forbid) monsooned beans.
- If possible, roast in a AC’ed room. Small air roasters are the most affected by mother nature.
- Try making an enclosure for your roaster - even a simple cardboard box will help.
By Ben C. on Sep 14, 2007
good points. the wet processed coffee/rainy day thing hadn’t occurred to me.
you’re right about ambient temperature — it’s a huge factor. though i’ll reiterate that airflow controls seem to greatly mitigate this impact. before, a programmed roast profile was completely at the mercy of surroundings. ‘twould seem that manual airflow adjustments allow you to compensate on the fly.
By bz on Sep 14, 2007
By the terms and conditions defined above, I can safely say . . . I am NOT baking my beans! Actually, regarding the exothermic reaction, I am comfortable enough with my profiles to know when to “juggle the first lid” just prior to first crack which gives an additional ramp (about 10 degrees if I’m not mistaken) to keep from stalling the profile. Without consultng my notes, I don’t believe I have ever stalled the temp for more than 30 - 45 sec. But, for the record . . . it is still a stall!
By nate the finger on Sep 14, 2007
Correct me if I am wrong. It appears, from Jaime’s previous link to the Carl Staub article, that the crucial issue regarding an exothermic reaction is that the bean does not lose heat (rather than simply stall):
“Once carmelization begins, it is very important that the coffee mass does not exotherm (lose heat) or the coffee will taste “baked” in the cup.”
So, would a stall (same temp for a duration of time without increased heat) even be classified as “baking”? To be clear, I am not even getting temp stall, I am just trying to sharpen my understanding of the roast process.
Regarding ambient temp: I agree, Ben. There is so much flexibility from an operator’s standpoint during the roast. Also, I have been greatly suprised by the consistency of each roast. So much so that I can predict when I will need to restrict air flow based on ambient temp, bean density, batch size, etc. At the end of the day it may be a ghetto way to roast beans, but I actually enjoy the ritual.
By nate the finger on Sep 14, 2007
i’ll take your last two at once. i think the point is that just AFTER first crack (when exothermy ends), is when you need to be careful not to let temps flatline. the beans go from exothermically giving off heat, which ADDS to the overall temperature, to absorbing heat. that transition can quickly cause the chamber temp to flatline or even decline.
stalling, or flatlining, is most consequential once sucrose has begun to melt. that’s caramelization, and once it’s begun you don’t want to let bean temps lose momentum or else, according to staub, you get baked tastes.
i think.
By bz on Sep 14, 2007
Nate,
It’s good to see you guys do the homework and get something out of it. Let a roast decline in temp mid first crack. Do a double hump where the temp falls and then rebounds during drying early in the roast. See how it tastes to test Snoz’s theory. Nothing is better than suffering… er, experience.
Define exactly what bakey tastes like and you will be able to identify it in others coffees as well as your own.
By Jaime on Sep 15, 2007
I am beginning to experience brain expansion and an increased browning reaction . . . I must be approaching the door of first crack! Be warned . . . I am preparing to exotherm!
I decided to pull out the old profile notes this morning. I logged:
A Harrar DP that increased approx. 5 degrees every 15 seconds entering into, and carrying through, first crack.
A Brazil PB that increased approx. 10 degrees every 15 seconds entering into, and carrying through, first crack.
A Brazil Yellow Bourbon that increased approx. 3 degrees every 15 seconds entering into, and carrying through, first crack.
In order to be totally transparent: I also found a few older profiles of a Yirg that declined 1 degree during first crack (just before a 10 degree ramp) and a Harrar DP with a 45 second stall at the end of first crack (just before a 30 degree incline!). Sadly, I do note have cupping notes on these batches, but I do recall a flat, characteristic-less cup of the Harrar! Could be the beans . . . they are a sample batch from a new supplier.
By nate the finger on Sep 15, 2007
you running a thermoprobe into your roaster? or are you trusting the onboard thermometer and pushing the “roast” button every few seconds to get a reading?
also, you mentioned earlier that you’ve never let temps flatline for more than 30-45 seconds. for a 10-minute roast, that seems like a “stall.”
By bz on Sep 15, 2007
Hence the disclaimer about “not referring to my notes” and the later “transparency” confession. However, this stall was one of my first roasts as a lid juggler. Since then there hasn’t been any.
Regarding the thermometer, I do not currently have an internal probe, I am going by the extremely inaccurate on-board reading. Disclaimer: I only use the temp to recognize incremental incline vs. temp stall/decline. I do not use it as a means of measuring temp. I am more in tune with the reactions occurring to the bean, not the temp at which it is occurring. For example, I recognize from bean color, smell, chaff, and sound what is occurring/about to occur and the on-board temp just informs me that there is a continual incline in heat.
By nate the finger on Sep 15, 2007
“I am more in tune with the reactions occurring to the bean …”
well excuuuuuuse me.
By bz on Sep 19, 2007