First crack: what it is and what to do when you hear it
If you have roasted for a while you know the sound. A dry, popping crackle, a bit like popcorn but softer, starting somewhere past the eight or nine minute mark on most drum roasters. That's first crack, and it's the one moment in a roast where the coffee tells you something without a thermometer.
What is actually happening
Green coffee holds a little water, and as the beans heat up that water turns to steam. Pressure builds inside a bean that has gotten hard and brittle from drying, and at some point the cell structure gives way and the bean splits along its seam. The pop is that split.
After first crack the bean has roughly doubled in size, the chaff comes off in a cloud, and the heat that was being used to drive off water starts changing the sugars and acids instead. That's why people say the coffee becomes "roasted" here. Before it, you are mostly drying and browning. After it, you are deciding what the coffee will taste like.
The temperature is a guide, not a rule
You will see numbers quoted for first crack, usually something around 195 to 200 °C on the bean probe. Treat that as a neighbourhood. Where you place the probe, how deep it sits in the bean mass and how fast the roast is moving all shift the reading by several degrees. The same coffee can crack at noticeably different probe temperatures on two different machines.
What matters is your machine's number, and whether it stays steady from batch to batch. If first crack on your Huila lands at 197 one day and 203 the next with the same recipe, something changed: the charge weight, the airflow, the gas, the weather in the shop.
What to write down
Three things, every batch:
- the time first crack started
- the bean temperature at that moment
- the time you dropped the coffee
From those you can work out how long you let the coffee develop, which is the single most useful number you can get out of a roast. We cover it in the guide on development time.
Mistakes people make around it
Listening too late. First crack builds from a few pops to a rolling crackle over about a minute. The first pops are the moment to note, not the loud peak. If you write down the peak, your development numbers will be consistently short.
Changing everything at once when it arrives. Many roasters cut the heat hard at first crack because they're nervous. That can stall the roast and leave the coffee flat and bready. A gentle, steady reduction usually does better than a big drop. How to read that is in the guide on rate of rise.
Confusing it with second crack. Second crack is a quieter, faster, crisper snap that comes much later and signals dark territory. If you are roasting for filter, you will probably never get close to it.
One habit worth building
Stand there for the first minute after first crack and don't touch anything. Listen, watch the temperature, note the time. It feels like wasted time but it's the clearest picture you'll get of what your roast is doing, and the rest of the guides here build on it.