Roasting Practice: Standard Process Guide · Coffee Roasting with Microwaves

Prerequisites (Step 0)

All microwave power settings and exposure durations specified in this guide are calibrated based on 144g of dry green coffee beans that have been washed and soaked for 30 minutes in a 50°C warm honey-fructose solution, reaching an initial batch weight of 180g to 190g.

Note
If you choose to roast dry green beans without the pre-washing and hydration steps, the initial moisture content and thermal mass will differ substantially. The power and duration profiles outlined below must be recalibrated accordingly.

Standard Operating Procedure

Step 1: Fitting the Lid

Fit the lid onto the heat-resistant borosilicate glass cylinder. This ensures rapid heating while circulating internal steam and convective heat.

Step 2: Placement on the Pedestal (Chopsticks)

Place the untreated wooden chopsticks across the center of the microwave floor, and stand the glass cylinder vertically on top of them.

Glass cylinder supported on wooden chopsticks

Step 3: Initial Uniform Heating (300W Preheating)

To eliminate thermal gradients, use low power (300W) to bring the batch up to just below the boiling point of water (approx. 90°C).

Protocol: 300W × 60s irradiation + 25–30s manual agitation × 4 sets
At the end of 4 sets, outer container temperature reaches approximately 90°C, and water vaporization reduces total weight by roughly 2.5g to 3.0g.

Set	Power	Duration	Agitation Interval	Target Temp
1	300W	60s	25–30s	-
2	300W	60s	25–30s	-
3	300W	60s	25–30s	-
4	300W	60s	25–30s	Outer wall ~90°C

Step 4: Primary Heating (High + Medium Power Cycling)

Drive off free moisture and accelerate the rate of temperature rise by alternating between 800W and medium power.
Never apply 800W continuously across consecutive sets, as this will scorch the beans.

Crucial Operation: Starting from this step, briefly burp the lid (open and close within 1 second) during each agitation interval to vent excessive steam before returning the container to the microwave.

Pattern A: Natural Process (Target: Light to Medium-Light Roast)

Naturals absorb heat rapidly; combine 800W with 600W.

Set	Power	Duration	Agitation Interval
5	800W	30s	25–30s
6	600W	40s	25–30s
7	800W	30s	25–30s
8	600W	40s	25–30s

Pattern B: Natural Process Standard (Target: Medium Roast)

Accumulates slightly more thermal energy.

Set	Power	Duration	Agitation Interval
5	800W	30s	25–30s
6	500W	50s	25–30s
7	800W	30s	25–30s
8	600W	40s	25–30s

Pattern C: Washed Process (Target: Medium-Dark to City Roast)

Washed lots carry higher water mass; use 500W × 50s to build substantial thermal momentum.

Set	Power	Duration	Agitation Interval
5	800W	30s	25–30s
6	500W	50s	25–30s
7	800W	30s	25–30s
8	500W	50s	25–30s

Step 5: Steady-State Heating (Crack Preparation via Medium Power)

As soon as bean surfaces begin showing light yellowing or browning, discontinue 800W bursts to prevent localized charring. Rely on medium power (500W or 600W) to distribute heat deeply and evenly.

Washed / Darker targets: Apply 500W × 50s for 2–3 sets, then transition to 600W × 40s.
Natural / Lighter targets: Apply 600W × 40s continuously for 3–6 sets.

Toward the latter half of this phase, bean shrinkage will halt, reaching the critical turning point where volume begins expanding again.

Step 6: First Crack Induction Boost (Apply as Needed)

If volumetric expansion (turning point) has not clearly manifested by the end of Step 5, apply 1 to 2 additional sets of "600W × 30–40s" to reliably drive the batch into the crack development threshold.

Step 7: Accelerating First Crack (Short High-Power Pulses)

To ensure first crack proceeds vigorously without stalling, alternate short bursts of 800W and 600W.

Power	Duration	Agitation Interval	Evaluation & Action Threshold
800W	20s	25–30s	Accelerate temperature rise
600W	20s	25–30s	Maintain temperature; monitor for onset of first crack
800W	20s	25–30s	Apply only if crack intensity is weak. Skip if strong popping is underway
600W	20s	25–30s	Peak first crack expansion

Step 8: Finishing and Roast Termination

Once first crack tapers off, fine-tune the roast toward your target development level using incremental bursts of "600W × 15s."

Medium-Light (Cinnamon to Medium): Terminate around the end of first crack (before any hint of second crack).
Medium (High Roast): Add 1 to 2 short sets following the conclusion of first crack.
Medium-Dark to Dark (City to Full City): Terminate immediately upon hearing the sharp, rapid snaps of second crack, or at its peak.

Step 9: Discharge and Rapid Cooling

Immediately discharge the beans into a cooling tray or stainless colander upon stopping.
Measure the bean surface temperature using an infrared thermometer.
Apply forced ambient air (using a blower, fan, or hair dryer on cold setting) to cool the batch down to roughly 30°C within 2 minutes.

Target Roast Level	Discharge Temp Guideline	Visual & Physical Characteristics
Medium-Light	~205°C	Light cinnamon color, surface creases present
Medium	~215°C	Chestnut brown, creases smoothing out
Medium-Dark	~225°C–229°C	Deep dark brown, light oil emergence on surface

Volume Dynamics and Power Profile Example

Ethiopia Gesha Village roast profile chart, 25 July 2026