Coffee: Roast Weight Loss — Mass Reduction During Roasting
Coffee loses 15–20% of its green mass during roasting: approximately 87% of that loss is moisture, with the remaining 13% comprising CO₂ release and volatile organic compound evaporation.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Total weight loss (light roast) | 15–16 | % | Percentage of green charge weight lost |
| Total weight loss (medium roast) | 17–18 | % | |
| Total weight loss (dark roast) | 19–22 | % | |
| Moisture contribution to weight loss | ~87 | % | Proportion of total mass loss that is water |
| Dry matter contribution (CO₂ + volatiles) | ~13 | % | CO₂ degassing and volatile organic evaporation |
| Green coffee moisture content | 10–12 | % | Moisture content of green beans before roasting |
| Roasted coffee moisture content | 1–2 | % | Target moisture in roasted coffee |
Weight loss during roasting is a practical and commercial reality that every roaster must account for. Green coffee is purchased by weight, but sold after roasting — meaning every roast produces a yield less than 100% of what was paid for. Understanding the magnitude, composition, and distribution of roast weight loss enables accurate pricing, yield planning, and roast profile assessment.
What Is Lost During Roasting?
Coffee bean mass decreases during roasting due to two categories of loss:
Moisture loss (~87% of total weight loss): Green coffee beans enter the roaster with approximately 10–12% moisture content (SCA green coffee standard targets 10–12%). During roasting, heat drives this moisture out as steam. By the end of the roast, finished roasted coffee should contain only 1–2% moisture. The bulk of this moisture evacuates during the drying phase (early roast) and continues through first crack.
Dry matter loss (~13% of total weight loss): As the roast progresses, CO₂ generated by the Maillard reaction and caramelization builds up inside the bean and is released — both during roasting and in the days after (degassing). Volatile organic compounds (aromatic esters, aldehydes, ketones) also evaporate as the roast proceeds. This dry matter fraction continues to off-gas after roasting, which is why roasted coffee bags use one-way degassing valves.
Weight Loss by Roast Level
| Roast Level | Total Weight Loss | Moisture Loss Component | Dry Matter Loss Component |
|---|---|---|---|
| Light | 15–16% | ~13–14% | ~2% |
| Medium-Light | 16–17% | ~14–15% | ~2% |
| Medium | 17–18% | ~15–16% | ~2–2.5% |
| Medium-Dark | 18–19% | ~16–17% | ~2.5% |
| Dark | 19–22% | ~17–19% | ~2.5–3% |
Calculating Roast Yield
Yield is the percentage of green charge weight recovered as finished roasted coffee.
Yield (%) = Roasted Weight / Green Charge Weight × 100
Example Calculation
| Parameter | Value |
|---|---|
| Green charge weight | 10,000 g (10 kg) |
| Roast level | Medium (17.5% loss) |
| Expected roasted weight | 10,000 × (1 − 0.175) = 8,250 g |
| Yield | 82.5% |
A roaster charging 10 kg of green coffee at a medium roast profile should expect approximately 8.25 kg of roasted coffee. Actual yield will vary based on ambient humidity, bean density, and roasting equipment.
Commercial Pricing Implications
Because green coffee is purchased by green weight and sold by roasted weight, roasters must factor weight loss into their cost-per-pound calculations. A 15% loss profile versus a 22% loss profile represents a significant difference in effective green coffee cost per sellable unit.
Effective green cost per roasted pound:
| Green cost | Weight loss | Effective cost per roasted pound |
|---|---|---|
| $6.00/lb green | 15% | $7.06/lb roasted |
| $6.00/lb green | 18% | $7.32/lb roasted |
| $6.00/lb green | 22% | $7.69/lb roasted |
Density Change During Roasting
As beans lose moisture and dry matter while simultaneously expanding in volume, roasted coffee is considerably less dense than green coffee. Green coffee density typically ranges from 650–850 g/L depending on variety, altitude, and processing. Roasted coffee density falls to 350–550 g/L. This density reduction affects grinder burr engagement, dosing consistency, and packaging volume calculations.
Weighing Protocol for Roasters
Accurate yield tracking requires:
- Weigh green charge on a calibrated scale immediately before loading.
- Allow the cooling tray to fully complete cooling (typically 4–6 minutes).
- Weigh roasted output on the same or a separately calibrated scale.
- Log both figures in roast software alongside curve data.
Weight loss data tracked over time provides a consistency metric: unexpected increases in weight loss can indicate charge temperature or airflow drift; unexpected decreases may signal moisture pickup in green coffee storage.