Weight Loss Targets
Weight loss is one of the most useful roast-output checks on Roest because it connects the roast’s final mass to moisture, heat application, batch size, pressure, and sensory outcome. It is not a standalone measure of development: two roasts can share the same loss and still taste different because the heat path, batch size, airflow, pressure, and bean structure differ. This page gives practical starting ranges, explains what moves weight loss, and shows how to use it alongside drop temperature, color, and tasting.
How to Calculate and Log Weight Loss
Weight loss is calculated from green weight and roasted weight:
weight loss % = (green weight - roasted weight) / green weight × 100
For example, 150g in and 135g out equals 10% loss source.
Log green weight, roasted weight, drop temperature, color if available, and tasting notes. Weight loss is most useful when compared against a known reference roast of the same coffee rather than treated as an absolute development score. Several experienced users use it mainly for consistency: once a target roast is dialed, matching final weight can keep repeat batches close, and one repeated 185g session produced 164.2g out within about 0.1g across batches 2 sources.
Weight-loss records can be distorted by retained or missing beans. Beans can remain in the chute, get under the cooling tray, or, under strong negative pressure, be pulled toward the exhaust; any missing roasted beans make calculated loss appear higher than it actually is 2 sources. The Roest logs page can display weight loss as an optional column, which makes routine tracking easier source.
Practical Starting Targets
Use these as starting points, then adjust by taste, drop temperature, color, and the reference roast for the same coffee. Green moisture, process, machine setup, batch size, and pressure can move the “right” number substantially.
| Coffee / use case | Starting weight-loss target | How to interpret it |
|---|---|---|
| General light Roest filter roast | 10.5–11.5% | This range was described as still light, with 11–12.5% suggested as an upper range for “light stuff” in one context 2 sources. |
| Most coffees when using starting moisture as a guide | Around the green moisture percentage | Christopher Feran generally looks for roast-loss percentage around the same as moisture content, often 10.5–11% for the coffees he buys source. |
| Washed Ethiopia / Kenya, Nordic-leaning light filter | About 9.6–10.8%, with Kenya often 9.2–10% in very light styles | Later low-loss approaches report washed coffees around 9.6–10.3%, with Kenya commonly 9.2–10%; other Ethiopia/Kenya examples sit closer to 10–10.8% depending on profile and moisture 2 sources. |
| Ethiopia washed at 150g, more conventional light target | 10.5–11% | A 150g Ethiopia washed go-to profile was reported at 10.5–11%, with Kenya “a bit more” source. |
| Very low-moisture or unusual Ethiopia lots such as Tagel | 8.6–9.7% may be valid | Tagel-specific reports found 8.6% enough and even preferred over 9% in one comparison; other Tagel references clustered around 9–9.7% 2 sources. |
| Natural Ethiopia / many naturals | Often 10.3–11.6% | Examples include Ethiopia naturals around 10.5–10.9%, 10.3–10.5% max for a specific Kabira natural, and 11.4–11.6% for another Ethiopia natural session 2 sources. |
| High-moisture natural anaerobic or fermented coffees | 10–12% commonly; 12–12.5% for some beans | High-humidity natural anaerobics were described as usually 10–11% and max 12%, while specific Honduras natural and Colombian fermented targets reached about 12–12.5% 2 sources. |
| Colombian Gesha / fermented Colombian coffees | Around 12–12.5% in reported examples | Colombian Gesha examples were reported at 12.3% loss and Colombian fermented coffees at 12–12.5% 2 sources. |
| 50g sample roasts | Often 10–10.8%, adjusted for moisture | Christopher Feran reported generally being at 10–10.8% depending on starting moisture; for a coffee reading 9.1% moisture on a Kett, he would look for 10.0–10.4% loss for a sample roast 2 sources. |
| More developed / espresso-leaning roasts | 13%+ can be intentional, but is no longer the light-filter default | Raising charge and doubling development time was described as pushing roasts into 13%+ loss, while espresso guidance included drying more water early, more caramelization, and a higher end temperature 2 sources. |
| Dark washed reference point | Around 16% was described as dark for a washed coffee with 9–10% moisture | This is a boundary example, not a light-roast target source. |
How to Adjust from the Target
When a roast tastes underdeveloped, green, thin, grassy, or hollow and weight loss is below the expected range for that coffee, first confirm that no beans were lost and that the target is appropriate for the coffee’s moisture and process. If the number is genuinely low, add energy earlier, raise selected inlet points, extend the relevant phase, or drop slightly later; one suggested Kenya adjustment was to raise early P1 inlet values to 150–160°C when a 9.5% / 50s-dev roast needed to move toward 10% source.
If weight loss is higher than desired and the cup is roasty, brown, bitter, or losing acidity, shorten development, reduce late heat, or reduce the conditions that are driving dehydration. A five-second reduction in development was described as enough to move color by 3–4 RoastMeter units in one context, and another comparison found that adding 15 seconds of development moved weight loss from 11.6% to 12.6% and color from 112 to 102 2 sources.
If more weight loss is desired for taste, increasing charge temperature can be preferable to simply adding a lot of development time, because long development can change the sensory profile more than the user intends source. For broader control of the final phase, see Development Time and Drop Decisions, Charge Temperature Guidelines, and Inlet Temperature Management.
Why the Same Weight Loss Can Taste Different
Weight loss measures mass removed, not the path by which that mass was removed. Equal weight loss can still produce different density, expansion, inside/outside color, aromatics, and cup quality. In one comparison, two coffees both lost 11.7%, but one was much more puffed and was expected to taste different; in another, three very different roasts all had 12.4% loss 2 sources.
Drop temperature and color do not fully solve this. A roast can share drop temperature and weight loss with another roast and still taste underdeveloped if the phase structure and heat application differ source. Color is useful for quality control, but it depends on sample preparation and device, and matching color does not guarantee matching taste; use Color Reading and Measurement as a supporting metric rather than a replacement for tasting.
Variables That Move Weight Loss
Batch size strongly affects loss on Roest. Lower batch weights tend to lose more, and 100g roasts are repeatedly described as having higher loss than 150–180g or 180g batches 2 sources. This is one reason weight-loss targets should not be copied directly between 50g, 100g, 150g, 185g, and 200g profiles; see Batch Size Scaling.
Roast time and heat placement also matter. Slower roasting generally loses more moisture, and even 30–60 seconds slower can develop the inside more while increasing loss 2 sources. However, high early heat can also increase weight loss, and a slow low-temperature start with a steep climb can reduce it source. This is why phase design in Drying and Maillard Phases matters as much as the final percentage.
Pressure and airflow can change loss by changing how moisture and heat leave the drum. More positive or near-zero drum pressure has been associated with lower weight loss, while more negative pressure has been associated with higher weight loss source. For pressure setup and measurement, defer to Pressure Management.
Airflow does not have a single simple relationship to weight loss across all Roest setups. Some experiments found slightly higher airflow produced lower weight loss but darker ground color, while other comparisons found higher airflow could increase color and weight loss, or that lower fan could produce more rapid development and more roast loss under equivalent inlet conditions 2 sources. Treat airflow changes as machine- and pressure-dependent, and validate with Airflow and Fan Settings.
Low-Loss Exceptions and When Not to Panic
Very low loss is not automatically underdevelopment. Several specific coffees were reported as tasting good at unusually low loss: Tagel at 8.6%, a Kenyan AA at 9.4%, and some low-moisture Ethiopia/Kenya roasts at 9–10% 2 sources. At the same time, 7–8% loss was also described as too low in other contexts because it suggested insufficient moisture evaporation source.
The practical distinction is sensory and structural. If low loss still gives clean acidity, sweetness, adequate aroma, good expansion, and no green or cereal aftertaste, it may be correct for that coffee. If it tastes thin, grassy, vegetal, cucumber-like, hollow, or weak, use the target table above and adjust the roast path rather than defending the number.
Measurement Caveats
Starting moisture is useful, but meter choice matters. The same coffee was described as reading 9.1% moisture on a Kett and about 10.0–10.3% on an Agratronix, which changes how a moisture-based loss target would be interpreted source. Quakers can also affect weight loss, and low-quality or mixed lots can make one target unreliable across a batch source.
Do not use weight loss alone to decide whether a roast is “developed.” Combine it with drop temperature, color, bean appearance, smell after drop, and cupping. For the sensory side of this loop, see Cupping and Sensory Evaluation, Resting and Degassing, and Roast Defects Troubleshooting.