What is Weight Loss in Coffee Roasting, and Why Does it Matter?

I track weight loss on every roast. It’s one of the simplest, most useful metrics you can log, and it requires no specialized equipment.

Why It Matters

Weight loss is a direct indicator of roast degree. A higher percentage means the beans went further into development, while a lower percentage means a lighter roast. Keeping track of this number helps you control consistency and dial in flavor. If a batch tastes too dark or roasty, you can aim for a slightly lower weight loss next time. If it tastes grassy or underdeveloped, target a higher weight loss by extending development or raising the drop temperature.

Once you find the sweet spot for a particular coffee, you can compare every future roast against that reference number. It’s an easy, reliable quality control tool that pays off immediately.

As a rule of thumb:

• Light roasts: 11–13%

• Medium roasts: 13–16%

• Dark roasts: 17–20% or more

How to Calculate Weight Loss

Start by weighing your green coffee before you roast. Weighing the same amount each time also helps with consistency. As soon as the beans come out of the cooling tray, weigh them again.

The formula is:(green weight – roasted weight) ÷ green weight × 100

For example, if I start with 12 lb of green coffee and finish with 10.44 lb roasted, the math looks like this:(12 – 10.44) ÷ 12 × 100 = 13% weight loss.

Variables to Watch

Moisture content plays a big role. If you loved one Ethiopian coffee at 12% weight loss, but the next bag tastes underdeveloped at that number, the new lot may have a higher starting moisture. A good rule is: for every 1% higher green moisture, you’ll need about 1% more weight loss to reach the same development.

Other things can throw off your numbers too: losing beans out the exhaust, forgetting to weigh your greens, or not taring the scale correctly.

Tools I Use

To double-check, I use a Coffmeter M1 moisture analyzer for green moisture. It’s made by DiFluid, accurate, and affordable. I also use their A1 color meter to check both whole bean and ground color. Ground color in particular is a very accurate measure of development, since it reflects the inside of the bean.

Weight loss is easy to track and highly valuable, but I always cross-check it with moisture content and color. Together, these three give me a clear picture of where a roast really landed.

—Corwin Peachey

Owner, Peachey Roasters and Peachey Coffee

Head Roaster, Peachey Coffee