Anyone who’s pulled a shot of espresso knows temperature and humidity can affect the pour. Many baristas adjust the grind and dose to compensate.
Similar factors influence the way we roast. You’ve probably noticed how light our dark roast coffees look the first day of 15-degree temperatures. We get at least one call per year wondering if we sent the right coffee! Rest assured we tell them, it will darken in a day or two at room temperature.
Warm summer temps age roasted coffee very quickly, while cold, dry winter weather slows the curing process
Our roasters Walt and Scott have to continually make adjustments depending on the conditions each day, and the age and moisture level of the green coffee they’re using. This is in addition to adapting to the variety of bean Brazil, Costa Rica, Sumatra, etc.
All three of our roast machines have read-outs. We typically set an ending temperature only as an emergency stopping point, monitoring each and every roast by hand. The first few batches can be an indicator of how things will be going that day.
I don’t want to leave out the importance of the age of green beans. Generally, green coffee – once processed – has a three to five month period when it is at its best. It will tend to dry some over time, which affects roasting.
Softer coffees, such as Brazil, Sumatra, some Mexicans, and others, develop more quickly. Harder beans, including Costa Rica and Kenya, more time. Coffees like Yemen Mocha are a devil to control. Scott and Walt use hundreds of signals, honed from their many years of roasting, to arrive at the result they are looking for.