Not to fire things up but has evaporative cooling been looked at as a cause for the drop?

It's called The Stall in the bbq world. The meat is trudging along and at about 160F or so, the juices start rising to the surface of the meat and actually stall the upward momentum of the meats temperature.

https://amazingribs.com/more-technique- ... l-bane-all

Moxiechef wrote:Not to fire things up but has evaporative cooling been looked at as a cause for the drop?

Yes that's what is being discussed.

I'm not saying I'm sure either. When my latest roast took off immediately after 1C I was shocked at how hard I had to put on the brakes by turning heat off and blasting the fan. There seemed to be more heat developing than I would have expected because of changes in air moisture and evaporation on the beans' surface. If I'd been cranking heat into the bean mass to overcome the dip, I might have managed a moon launch! Not enough to rest a case of course ...

It's not evaporative cooling specifically, as the water leaving the beans has already evaporated to steam (that's what creates the pressure needed to cause first cracks). But that steam is coming from the center of the beans, which is a slightly cooler environment than the air surrounding the beans, so it counteracts the rising heat of the roasting chamber, leading to a dip in ROR.

Boldjava wrote:...
There is no instrumentation which can measure the inside temp of the bean at this point.
...

You sure ? http://claycritters.com/coffee/Bollinge ... oaster.jpg

"You sure ? http://claycritters.com/coffee/Bollinge ... oaster.jpg"

A true sample roaster!

Now seriously... ever seen a thermocouple active area, the junction ? Is pinhead sized, there is no technical difficulty to make a bore in a bean, host inside the thermocouple junction, and measure true BT.
Of a single bean though... which could have different thermodynamics than the fluid mass of the beans, because will be exposed to hot air only, no drum touch, no agitation.

I am guessing inserting a probe into a bean for reference wouldn't be accurate either. I could very well be wrong, but I am pretty sure removing a chunk of the inside of a bean and inserting something that will conduct heat straight to the center of the bean would make the bean heat faster than the other beans.

renatoa wrote:Now seriously... ever seen a thermocouple active area, the junction ? Is pinhead sized, there is no technical difficulty to make a bore in a bean, host inside the thermocouple junction, and measure true BT.
Of a single bean though... which could have different thermodynamics than the fluid mass of the beans, because will be exposed to hot air only, no drum touch, no agitation.

And telemeter it out, or keep the wire (thermal conduit) into the center of the bean where it can carry heat right past the more insulative bean straight inside of it?

As for the rest of this topic......

Although I appreciate and try to listen to new ideas, I give a lot of credence to the roasters I talk to that have been doing it for decades. These new book writers were watching their parents drink coffee when today's highly experienced roasters were honing their trade. I taste their coffee and then I tend to believe. Even the latest "experts" say that they have a lot to learn, and if they don't then they probably aren't worth listening to. All in all it's just general trends based on limited information and the best thing to do is just try them all ... and then taste the coffee.

Down from soapbox now. Happy roasts!