← Roasting guides

Weight loss in roasting: what the percentage tells you

The easiest check in a roastery needs a kitchen scale. Weigh the green coffee going in, weigh the roasted coffee coming out, and work out how much was lost. That's weight loss, and for most coffees it falls between about 11% and 20%.

Where it goes

Mostly water. Green beans carry roughly 10 to 12% moisture, and most of that leaves in the first part of the roast. Past that, a bit of chaff and some of the bean's own mass turns to gas as it browns. The darker you go, the more you lose.

8 %12 %16 %20 %Light11–13 %Medium13–15 %Dark15–20 %Weight lost in the roast, %
Typical weight loss by roast level. These are common ranges, not targets; a different moisture or a different machine will shift them.

Why it's worth tracking

It's a sanity check that doesn't need a probe. If a batch that's supposed to be your usual medium comes out at 11%, you either dropped early or your scale slipped. If a dark roast shows 13%, something is off: either your measurement or what you called "dark."

It's also how you know how much coffee to expect. Planning sales, labelling bags and working out cost per kilo all rest on the real yield, not the green weight.

And it catches changes in the green coffee itself. Beans that arrive drier, or have sat in a warm store for a year, lose less weight at the same roast level. A drift in your numbers across a season is often the coffee, not you.

How to measure it properly

  • Weigh the green just before the charge, not what you wrote on the lot sheet.
  • Let the roasted coffee cool fully before weighing it. It's still hot and a little steamy at the drop, and that moisture is part of the number.
  • Use the same scale every time and check it with a known weight now and then.
  • Write both numbers down. Working it out in your head and writing only the percentage loses the original data.

Things that mislead

Different coffees lose different amounts at the same colour. A dense, hard bean can look identical to a soft one and sit a point or two apart.

Weight loss is about how much mass left, not how well the coffee developed. Two roasts can lose 14% and taste nothing alike. Use it alongside development time, not instead of it.

Finally, don't chase it. It's easy to stretch a roast just to hit a percentage. Weight loss is a symptom, and treating the symptom gives you worse coffee.