I’m reading Matt’s article in the Barista Hustle about coffee being baked in the final stages of a roast. I always thought that stalling was supposed to lead to baked flavors but he is saying that the RoR increasing towards the end of the roast is what causes this to happen.
At the end of the roast, the coffee beans are quite dry and fragile. Small, brief changes in temperature can make or break the whole roast. Here is an excerpt from his blog, “Let’s Talk About Roasting.”
If the coffee experiences an increase in speed somewhere after first crack, that will “bake” the coffee. This is characterised by the coffee exhibiting a lack of sweetness and/or dark roast flavours, even though it might not be a dark roast. You can finish a light roast with a bake that will then taste a little bit bland, ashy or dry. Not ideal. Try not to fall into the trap of calling a baked roast “dark” (it happens all the time and you’ll look like a dingus). Look out for dryness, a lack of sweetness, dull acidity, and in worst cases; ash. Sang Ho from Square Mile Coffee Roasters introduced me to calling this the “Flick of Death”. Precisely. It kills the party.
If the coffee temperature stops increasing for a significant amount of time, it’s called stalling. Sometimes, the coffee might stall so hard for so long that the temperature starts to drop a few degrees. The worse the stall, the less developed the coffee will be. It’s super hard to pick this one out without seeing a roast profile. If you start calling out roasts for stalling without seeing the profiles be prepared for a slap. Stalling can create weird thinness, waxy cardboard flavours, sharp acidity and sweetness that’s frail and lacklustre.
The coffee can’t experience an increase in speed, and it can’t stop, but it should still be rising in temperature after first crack. At first glance this might seem impossible, but it’s not that hard. Just think of a car constantly slowing down until it reaches a stop sign. Before and during first crack, the coffee should be increasing in temperature quite quickly. This momentum carries it further and hotter after first crack, and allows for a constant slowing until the end. The ideal end of roast is constantly slowing down after first crack until the speed approaches or reaches zero right at the end. This results in no baking and no stalling. If you don’t notice any problems with the coffee, it was likely ideal.
This comment is interesting: