I've only roasted at altitude; I have zero experience roasting at sea level. My house is at around 5850 feet of elevation (~1900m).

Based upon my own experience, in contrast to what I have read on the internet, it is my impression that coffee does not roast at altitude the way that it roasts at sea level. I believe that my roasting experience is different than I would have at sea level, but I do not know in what way or why (other than presumably the reduced oxygen content of our air, and the lowered atmospheric pressure). My own observation is that the cracks occur at higher temperatures (measured by a bean mass TC) than what I read posted by people who roast at sea level. It could be, however, that this is just a function of where my bean mass TC is located within the particular drum I roast in.

Bernie Digman's cafe and roasting business is in Las Cruces, NM, which appears to be at around 4000 feet of elevation. I'm not sure if that is high enough to effect roasting, but I'm sure that Bernie knows the answer.

I was curious to know if anyone knows how altitude effects the roasting process, in observable ways such as the temperatures that the cracks occur, etc. Obviously, gases combust differently at altitude and that does effect the heat source when one is roasting with gas (as I do) however that isn't really what I'm getting at; I'm interested in the bean roasting process itself.

Does anyone have any useful observations? I'm not interested in theories or regurgitation of unsubstantiated stuff that may have been written or posted before, rather I'm interested in provable facts.

Thanks,

ken

You are probably right; it is certainly true of all other baking and roasting.

The problem is that everyone gets different temperature readings for the cracks due to sensor placement, bean moisture content, and profile differences (a dry coffee or a slow approach to the first crack creates a higher temperature first crack and lower temperature second crack due to lower moisture content slowing the escape of the steam, and accelerating the breakdown of the cellulose). You'd need to ship the same roaster and beans to different altitudes, then roast at the same weight and profile, to know for sure.

My sample roaster has a hacked in bean probe that is surrounded by swirling beans during the roast:



Depending upon the bean and slight variations in my roast profiles, I'll hit the onset of first crack around 423F to 425F, at around 8 to 9.5 minutes into the roast.

I also have an M3 Quest, and although it does not behave exactly the same, it hits first crack within a few degrees F. of what I reported above in my sample roaster.

With the type of profiles I use, where I try to extend the time in between the onset of 1st crack and the end of the roast, 2nd crack, if I roast that far (rarely) begins around 437F. I usually stop my roasts at between 432.5F and 434F.

When I read roast descriptions on the internet I read about first crack starting around 398 to 408F, not higher than that. I read about roasts being terminated quite a bit lower than what I report above.

Obviously, some of this can be explained by roaster particularities and the vagaries of probe placement, still, I think that altitude is playing a role here.

Has anyone else who roasts at altitude made similar observations?

ken

Hi Ken,
I'm a newbie roasting at close to 10,000 feet altitude. I roast on a Quest M3 and first crack arrives around 380F. I still haven't managed to translate all the info on roast profiles available into something I can use. Looking at the bean color my beans seem to be done drying at a lower temp as well. I'd sure love to get some advice from someone roasting at altitude. It seems that I need to roast into 2nd crack which I get around 420F.