Coffee roasting charge temperature is the drum temperature at the moment green beans go in, and it sets the thermal momentum for everything that follows. Get it wrong and the roast either stalls and bakes or scorches the surface before first crack. This page gives you a calculator, a chart in °C and °F, the method for measuring bulk density, and the adjustment Indonesian wet-hulled coffee needs.
Charge temperature is the drum temperature you drop green coffee into at the start of a roast. It determines how much stored energy the machine hands the beans in the first two minutes, which decides whether the roast carries through drying and Maillard with enough momentum to finish cleanly.
Charge too low and the bean temperature curve flattens early. You get a baked, flat, papery cup that no amount of heat later in the roast repairs. Charge too high and the surface tips and scorches while the core stays underdeveloped.
Enter your species, bulk density class, measured moisture, and target roast level. The calculator returns a suggested charge temperature range in °C plus a grind size reference for V60 pour over, French Press, Espresso, Moka Pot, and Cupping.
Treat the output as a starting point to test, not a setting to trust blind. Roast it, read your rate of rise, then adjust.
Charge Temperature Chart: Baseline and Adjustments
Charge temperature works as a baseline plus corrections, not a lookup value. Commonly cited ranges put single-walled gas drum roasters at 196°C to 204°C (385°F to 400°F) on a standard batch, while double-walled machines such as the Diedrich IR run hotter. Set your own baseline on medium-density Arabica at 11% moisture, then move from there.
| Variable |
Condition |
Adjust charge by |
| Bulk density |
High, 700 g/L or above |
+3°C to +6°C |
| Bulk density |
Medium, 650 to 690 g/L |
Baseline |
| Bulk density |
Low, 640 g/L or below |
−3°C to −6°C |
| Moisture content |
Above 12% |
+2°C to +4°C |
| Moisture content |
10% to 12% |
Baseline |
| Moisture content |
Below 10% |
−2°C to −4°C |
| Roast level |
Light |
+2°C to +4°C |
| Roast level |
Dark |
−2°C to −4°C |
| Batch size |
Near maximum drum capacity |
+5°C to +10°C |
| Batch size |
Below half capacity |
−5°C to −10°C |
Mill City Roasters frame density and moisture the same way: a denser, wetter bean absorbs more energy before it responds, so it needs a higher charge, while that same charge scorches a soft, dry bean. On batch size, Roast Magazine puts practical maximum capacity at roughly 80% of stated drum capacity.
Move one variable at a time. Two changes at once tells you nothing.
How to Measure Green Coffee Bulk Density
What roasters call bean density is almost always bulk density, the mass of beans filling a known volume, air gaps included. True density needs water displacement and a lab. Bulk density is what predicts roasting behaviour, and you can measure it on a kitchen scale.
- Weigh the empty cylinder. A 100 mL cylinder works best. Record the weight, then tare.
- Fill to exactly 100 mL with green beans. Do not shake, tap, or compress, since settling changes the result by 20 g/L or more.
- Weigh the full cylinder and subtract the empty weight.
- Read the result. 100 mL equals 100 cm³, so the mass in grams gives you g/cm³ directly. Multiply by 10 for g/L, the unit most roast software uses. 72 g in 100 mL is 0.72 g/cm³, or 720 g/L.
- Repeat twice and average. Single readings vary more than the differences you are trying to detect.
| Class |
g/cm³ |
g/L |
Typically |
| High |
0.70 and above |
700 and above |
High-altitude washed Arabica |
| Medium |
0.65 to 0.69 |
650 to 690 |
Arabica, Excelsa |
| Low |
0.64 and below |
640 and below |
Robusta, Liberica, wet-hulled Sumatra |
One correction worth making. The float test does not grade density, it flags defects: beans that float are usually insect-damaged, hollow, or badly dried, and they belong in the reject pile.
Need bulk density and moisture readings before you buy? See our current pricelist or contact our team for lot specifications.
Why Indonesian Wet-Hulled Coffee Needs a Lower Charge
This is the adjustment most roasters miss on their first Indonesian container, and it is the reason Sumatran coffee has a reputation for being difficult in the drum.
Arabica Gayo, Sumatra Mandheling, and Sumatra Lintong are semi-washed at the cherry stage and then wet-hulled (Giling Basah), with parchment stripped at 35% to 40% moisture rather than the 12% to 13% of dry-hulled lots. The bean swells and finishes drying in an open, exposed state. What arrives is a bean with lower bulk density, a wider, splayed shape, and a more porous cell structure than a full-washed, dry-hulled Bali or Java lot of the same screen size.
Practically, that bean takes surface heat faster and holds less thermal mass. Run your washed Arabica charge on it and you will tip the edges before the core catches up.
Start 5°C to 8°C below your washed baseline for the same batch size, and open airflow slightly earlier to even out the irregular bean geometry. Every lot we ship carries a moisture reading against SNI 01-2907-2008, so you can set the charge before the container lands rather than burning a batch to find out.
Grind Size Reference by Brew Method
The calculator returns grind sizes alongside charge temperature so you can carry one roast through to the cup. The micron ranges below are the reference points.
| Brew method |
Grind |
Microns |
| Espresso |
Fine |
200 to 400 |
| Moka pot |
Fine to medium-fine |
300 to 500 |
| V60 pour over |
Medium-fine |
400 to 700 |
| Cupping |
Medium-coarse |
700 to 900 |
| French press |
Coarse |
800 to 1,200 |
Cupping follows the SCA protocol, which specifies 70% to 75% of particles passing a US 20 mesh sieve, roughly 850 microns. For a fuller breakdown by brewer, see our guide to coffee grind sizes.
Frequently Asked Questions
What is charge temperature in coffee roasting?
Charge temperature is the drum temperature when green coffee enters the roaster. It sets how much energy the beans receive in the first two minutes, which shapes the whole roast curve. Too low produces baked, flat coffee. Too high scorches the surface before the core develops.
What charge temperature should I start with?
Single-walled gas drum roasters commonly work between 196°C and 204°C, or 385°F to 400°F, on a standard batch. Double-walled machines run hotter. Establish your own baseline with medium-density Arabica at 11% moisture, then adjust for density, moisture, roast level, and batch size.
Does bean density change charge temperature?
Yes. Dense beans absorb more energy before they respond, so they take a charge 3°C to 6°C above your baseline. Low-density beans need the same amount taken off, because a high charge scorches them. Measure bulk density in g/L rather than guessing from origin.
How does moisture content affect charge temperature?
Higher moisture means more energy goes into evaporation before the bean heats, so wetter coffee tolerates a charge 2°C to 4°C above baseline. Green coffee below 10% moisture needs the same reduction. Most specialty green coffee arrives between 10% and 12%.
How do you measure green coffee bulk density?
Fill a 100 mL cylinder with green beans without shaking, weigh the beans, and divide by volume. Since 100 mL equals 100 cm³, the mass in grams gives g/cm³ directly, and multiplying by 10 gives g/L. Repeat twice and average the readings.
What charge temperature suits Sumatran wet-hulled coffee?
Start 5°C to 8°C below your washed Arabica baseline. Semi-washed, wet-hulled lots from Gayo, Mandheling, and Lintong have lower bulk density and a more open cell structure, so they take surface heat faster and tip at charges that suit a dry-hulled washed coffee.
Buy Indonesian Green Coffee Beans from Indonesia Specialty Coffee
Indonesia Specialty Coffee supplies Grade 1 Specialty green coffee at 82 to 88 SCA points, graded against SNI 01-2907-2008 with moisture at or below 12.5% and a defect value of 11 or lower. We ship FOB Belawan from Medan, and every lot is Halal certified, with Organic and Rainforest Alliance available on request.
Order tiers run 1 kg cupping samples, 60 kg microlot, 350 kg wholesale, and container loads from 9 MT quoted per metric tonne.
Dialling in a new Indonesian origin? Take a 1 kg sample, run it against the chart above, and see where your charge lands. Browse our green coffee beans or check the pricelist for a quote.
