How do you approach roasting in 80%+ Humidity


So I was just wondering how everyone here approaches roasting when it come to high humidity?
From what I’ve understood; warmer climate air with high humidity holds much more water than cold climate high humidity but how does that affect your approach regarding PH, P, F, D settings? if at all?


I’m hopeful this turns into an informative discussion. I live on the US Gulf Coast, where high humidity is the norm. Right now, I store my beans in the insulated, A/C- cooled house, but have to roast out in the uncooled, uninsulated garage. I have plans to build out an insulated and air conditioned roasting room, but I’m not there yet. I don’t really have a good comparison of the same coffee roasted in the garage versus indoors proper; maybe I can talk my spouse into letting me roast under the vent hood a time or two. :slight_smile:

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@matt_h and @jpndemir I live in a very humid area too (south-central Georgia) and I have also thought about this. While I do not have any idea about whether humidity makes any difference or not, I am thinking of roasting some beans this weekend when it will be more humid and then roast the same beans in December when the humidity is lower and see if there is any major difference or not. Of course in our region low humidity also means low temperature. So I am not sure if I can pinpoint the result of humidity (if any) or not. But we shall see.

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@krishroy and @matt_h

Since no superstar is swooping in with answers I guess we will have to do some comparisons, collect data and reconvene in a few months :stuck_out_tongue:

There’s got to be others in Asia in these forums roasting in higher humidity conditions than those of us in the US.

@cash0612 - if I recall you’re in India? Depending where, do you have humid conditions in 80%+ range?

I roast under the vent hood in MA - it works well but make sure you open up a window close by as well, it’ll help mitigate the lingering smell afterwards.

Our Monsoons are very, very damp with humidity often exceeding 90%. We also have frigid winters with sub 5°C temperatures, so that has made roasting quite challenging. In general, bean storage is more of an issue though grainpro bags do alleviate the issue to quite an extent.

Roastwise, I feel the drying phase is impacted most by humidity in terms of time to milestones. Once the yellowing is over the malliard and development happens normally, but since the drying phase itself is extended, the rest of the milestones also occur later than at dryer times. Just my observation that is.

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I’m in the Po valley in Italy and we do get high humidity here. I just don’t understand if this is a question for outdoor or indoor roasting. All of my September roasts were done when the humidity outside was well over 80%. You can look them up on roast world. I just do indoor roasting with inline fan and a large activated carbon filter on my balcony. As you can see the humidity inside is nowhere near 80% because it can’t be. And the Bullet will dry the air a bit while preheating and roasting. If you look at September 4 roasts you’ll see that the humidity has dropped by 2% while I was roasting. As for the other part of the question, the humidity will affect the roast, but only the humidity absorbed by the coffee you’re storing. The drum, once preheated, is hot and dry, it’s the coffee you’re putting in that will make the difference. If you don’t have an isolated space where you store your coffee and it’s exposed to high humidity, you should get a coffee moisture meter and measure the humidity prior to your roast. More humidity=more heat. Coffee should have around 10-12% moisture content and anything more will take a bit more heat to evaporate. Of course, it is impossible to determine coffee moisture any other way.

This takes math?!

The assumption is correct - warm air has a higher capacity to hold water than cold. And water absorbs more energy than air. So, for a kg of air at 45C and 90% humidity, technically you have more water and ‘rob’ more bean-heating energy than in air at 20C and 90%. There are fancy plots that illustrate this. So, in warm air of X% relative humidity, your roaster is less efficient in terms of heating beans than in cold air with the same relative humidity.

But in reality? 1kg of 40C air at 50% humidity holds about 23g of water. 1kg at 20C at 50% holds about 7g.

This is where it gets complicated and we need more data … We need to know how long it takes a Bullet to pull a kg of air through the machine. For that, we need to know the volume of air through the machine over time. If the machine pulls a kg of air through in 1 min (it doesnt), then relative humidity would be important. If it takes hours (Im not sure) then it is irrelevant.

How’s that for a long non-answer :thinking: :sweat_smile:

It’s a good non-answer, but it’s not complete. We would need to know how long it takes for Bullet to pull a kg of air through on all fan settings, 1 through 9, and let’s not forget that the fan is introducing cold air, in order to slow down the roast, that mixes with hot air already being introduced by another fan. I admit, it is a bit of a conundrum. :sweat_smile:

Braca you’re 100% right, I gave up at the ‘air in’ stage. Too much thinking to be done :wink: But I wonder if the delta of water in is in the noise :thinking: