Recent heat wave with high humidity and been doing some very light roasts. I can't help but think the increased moisture raises havoc with the roasting processes. And might especially be a significant factor when light roasting. Steaming the beans seems like it would change a bunch of chemistry going on. And can only see this creating a poorer/off cup. Air needing to be dry coming in efficiently heating and flushing produced moisture.

I feel like I've read electric roasters were not as good as gas because of the lack of moisture. It's well known the some of the best coffee is roasted on a Loring, and you can bet that is some humid air. If anything, lower roasting temps are allowed due to higher convective rates. I don't believe in this "flushing moisture" idea you pitch. At 400F+, water is either chemically bound or quickly evaporated.

It's less known that the Loring has been quite frustrating some highly experienced users.

Ive actually been thinking about this alot. It seems more moisture would be beneficial to the beans, since there are chemical changes that are contingent on water. A humid environment should tranfer heat more efficiently and gently as well. Its why roasts coming out of the quest have cracking at the ends of the beans, and roasts coming out of gas roasters often dont have split ends (possibly its the cast iron drum used in a lot of roasters too).

I won't be attending the roasting summit in France later this month but maybe can get a question asked to Joseph Rivera who will be attending and a panelist. I've heard roaster troubles at both ends of the spectrum of too dry and too humid incoming air. But what is considered more ideal or an issue during various phases I've yet to find good info.

With more thought, I think there might be something to this. Considering how airflow alone has such an impact on flavor, and considering that thick stewed flavor from diedrich roasters compared to the thin taste of a similarly stretched air roast.

I've also recently come to learn that most roasters with a Loring also keep an SF-25 or L-12 around for the coffees that matter.

farmroast wrote:I won't be attending the roasting summit in France later this month but maybe can get a question asked to Joseph Rivera who will be attending and a panelist. I've heard roaster troubles at both ends of the spectrum of too dry and too humid incoming air. But what is considered more ideal or an issue during various phases I've yet to find good info.

Please report back if you ask him, I would love to know what he thinks!

+1; +1 Great discussion guys.

I notice issues roasting during high humidity, and when raining. In the summer my pooch potential goes way up.

My theory is that the very hot roasting air has a large capacity for water vapor. Humidity doesn't likely effect local chemical availability as much as it does add another variable in convective heat transfer.

http://link.springer.com/article/10.100 ... 3480050161

... For molar fractions of water vapour up to 0.27, the heat transfer increased with increasing humidity. The ratio of heat transfer rates in humid air and dry air is a unique function of the molar fraction of water vapour, independent of the air temperature and flow velocity.

So I decided to try and run a test by adding water to the roaster mid roast. I suppose this shouldnt be a huge shocker, but it made the roasts flat and flabby. I used a coffee I have roasted a ton of, so I know how this coffee can taste. Its hard to describe in words, but the roasts with added humidity were lifeless. Like a stalled/ old coffee. Of course adding water/steam mid roast changes the thermal dynamics of the heat transfer, so with each burst of water the rate of rise changed. Generally slowing things first, and then speeding things after.