Coffee Roast Loss Calculator

In short Coffee loses weight in the roaster, and the number is bigger than most people expect: 12 to 14% for a light roast, 15 to 17% for a medium and up to 22% for a dark. A kilo of green comes out somewhere between 780 and 880 g. Most of that is water — green coffee carries roughly 10 to 12% moisture and leaves the roaster at 2 to 3%, which accounts for the bulk of it on its own — and the rest is organic matter driven off as the beans develop, which is why darker roasts lose more. THERE IS A PERCENTAGE TRAP HERE AND ALMOST EVERYONE FALLS INTO IT. Losing 15% of the weight does not make roasted coffee 15% dearer per kilo. You have to divide by what is left rather than add back what went, so the multiplier is 1 ÷ (1 − 0.15) = 1.1765, not 1.15. At a 16% loss it is 1.1905. The gap looks small at roasting losses and it is not small in general: at a 50% loss the true multiplier is 2 and the naive one says 1.5. Get this wrong on a price list and the error compounds through every bag. Roast loss is a measurement, not a setting. You cannot dial in 16% — you roast to a colour, a time or a flavour, and the loss is whatever it turns out to be. That is why this page works in three directions: forwards from green, backwards from a target roasted weight, and from two weighings to tell you what the loss actually was. Recording it every batch is the cheapest consistency check a roaster has, because the same green taken to the same loss is very nearly the same coffee, and a batch that comes out two points off tells you something went differently before you have even tasted it. One thing the arithmetic cannot see: green coffee moisture varies by origin, by processing and by how long the sack has been sitting. A wetter green loses more for the same roast, so comparing losses across different lots says less than comparing them within one.