Exothermic Rise at 10 minutes

Greetings Roasters, I’ve been roasting on the bullet for a year now. I always roast 700 grams so that is one constant. I preheat to 270 C and add beans when the lady tells me too. I guess my roasts are ok, except at about 10 minutes I get a pretty good sized exothermic heat-up. Would one of you more seasoned roasters look at this and maybe have an idea for me? Is it an issue at all? Thank you all for your time and energy. Cheers Simie

When you say “I guess my roasts are ok”, care you referring to the taste of the resulting coffee, or the aesthetics of your roast curve?

What coffee are you roasting here? How long after roasting are you trying it, and what’s your preparation method? Did you like the flavor? Were there flavor aspects that you were trying for but did not get?

I think with those answers, the good folks here will be far better equipped to help.

To just make the roast curve conform to the declining ROR “ideal”, take notes about how the coffee responds during the development phase, and then be prepared to do a larger power drop in anticipation of that little kick you see at the end. I’ve found that the way a particular bean develops in the Bullet to be extremely repeatable, especially if your batch size and ambient temperature is consistent. You can use the overlay feature to help work out when to drop power when stretching out development.

On this one, I was roasting a Kenya Muranga Karugiro Peaberry, Most of my roasts do the same thing at about the same time. When I said my coffee was ok I was understating a bit, my coffee’s come out very good in flavor, but I was wondering if the exo-rise at the end had any consequence such as removing sweetness in the cup. I’m still pretty new, but man I love to roast and start my day off with my home roasted fresh coffee. Two hours of bliss.

I typically consume my coffee about two to three days after roasting and roast once every ten days or so. Temps in the 50-60 F range when I roast, humidity about 52. Thanks all for your time. Simie

I’ve had this on a number of roasts, over a number of different origins. I find it’s not linked to time but to temperature - 360 to 365 degrees F (182-185C) usually sees a spike in temperature that can be mitigated with a well-timed boost in fan.

My theory at least is that this is a point in the roast when the seed begins to absorb less heat as it approaches first crack, and the blip in the ROR is really just the excess heat captured in the drum. 20 seconds later the seed is back to absorbing heat and the ROR normalizes. If my theory is correct then there’s not much benefit to controlling the blip. However I haven’t really cupped the “blip” vs “non-blip” roasts next to each other to say if there’s an impact.