One of the biggest misunderstandings about utilizing a color machine are widespread expectations about the unification of measurement. And they’re unfortunately wrong!
Although the majority of colormeters use the “Agtron” scale, the roast degree expressed by a number on the screen is your local, not universal variable. Your 100 might be someone else’s 93 or 107. And here are three main reasons why:
- different systems of measuring (variety of tools, shapes and methods of distributing grinds in dedicated plates)
- different grind size (coarser grind casts more shadow hence tends to give “darker” degrees, finer ground casts less shadow and is easier to distribute more flat, hence tends to give “lighter” degrees)
- different sensitivity (although many brands utilize the same “Agtron” scale, the quality, precision and sensitivity of measurements may vary from model X to model Y)
Calibrate to YOUR readings. The information input of “I roast my Kenyans to 103 on machine X” is useless without context. It only makes sense to compare different roasts within the same technique, same grind size on the same colormeter, ideally using the same grinder.
I recommend using a relatively fine ground for greater repeatability. Always the same setting! Create a routine that’s efficient and repeatable. Measure your roasts cooled down, but before the end of the next batch, so you’re always on the right track and have time to make a good decision before the end of the roast.
Our Roasting Tips are brought to you by Piotr Jeżewski (88 Graines Q Grader & Sourcing Director)