Roasting Case Study: Ethiopia (Natural / Medium-Light Roast) · Coffee Roasting with Microwaves

This document is an empirical log recording the roasting of an Ethiopian dry-processed (natural) green coffee to a medium-light roast, executed in accordance with the Standard Process Guide.

Roast Date: August 22, 2026

Batch Specifications (Step 0)

Parameter	Set / Measured Value	Notes
Coffee Origin / Lot	Ethiopia Sidama Baturo (2024/2025)	-
Variety	74158	-
Processing Method	Natural (Dry Process)	-
Input Green Bean Weight	144.0g	Standard unit (1kg bag divided into 7 batches)
Washing Water Temp	50°C (Purified water)	Chaff and floater culling
Soaking Solution	50°C water + 15g honey + 20g fructose	30-minute soak
Post-Soak Bean Weight	183.3g	Measured after removing 2.0g of defective floaters
Initial Bean Temp	30.2°C	Infrared reading immediately before roasting
Initial Bed Volume	275ml	Visual cylinder reading
Total Weight (incl. container)	452.3g	-

Profile Projection
With a post-soak weight of 183.3g (low 180g range), this lot exhibits high cell density and relatively low water absorption. Thermal transmission is anticipated to be rapid, meaning roast progression will likely accelerate. Care must be taken to avoid excessive thermal input leading to over-roasting.
Furthermore, this variety frequently displays a rate-of-rise deceleration following the onset of first crack; adequate thermal momentum must be preserved when entering first crack.

Detailed Roasting Operations

Steps 1–2: Setup

Attach the lid to the container and position the cylinder vertically on top of the wooden chopsticks centered on the microwave floor.

Step 3: Initial Uniform Preheating (300W)

No.	Power	Exposure	Agitation Interval	Volume Trend	Operational Notes
1	300W	60s	21s	275ml	Preheating initiated
2	300W	60s	23s	300ml-	Slight volume increase from vaporizing internal moisture
3	300W	60s	24s	275ml	Minor packing fluctuation during agitation
4	300W	60s	49s	275ml	Interval extended for intermediate weighing

Step 3 Cumulative Heat Input: 72k Ws (300W × 60s × 4 sets)
Step 4 Pre-check Metrics: Outer wall temp 91.7°C / Total weight 449.2g (Moisture loss: 3.1g)
Assessment: Exceeding 91°C with >3.0g of moisture evaporated by Set 4 confirms highly efficient heat absorption. A fast profile terminating around 24 total steps was selected.

Step 4: Primary Heating (High + Medium Alternating)

Accelerate moisture evaporation. The lid is burped (opened and snapped shut for <1s) during each agitation interval.

No.	Power	Exposure	Agitation Interval	Volume Trend	Operational Notes
5	800W	30s	29s	300ml	Rapid temperature rise
6	500W	50s	32s	300ml	Thermal energy accumulation
7	800W	30s	29s	275–300ml	Shrinkage begins as moisture vents
8	600W	40s	30s	275ml	Initial light-tan coloring observed. 800W discontinued

Step 4 Interval Heat: 97k Ws / Cumulative Total: 169k Ws

Step 5: Steady-State Heating (Uniform Conduction via Medium Power)

To prevent premature scorching of natural sugars, 500W × 50s was bypassed in favor of 600W × 40s as the standard cycle.

No.	Power	Exposure	Agitation Interval	Volume Trend	Operational Notes
9	600W	40s	23s	275ml	Progressive drying
10	600W	40s	27s	250–275ml	Coloring advances (mottled yellow-brown)
11	600W	40s	29s	250–275ml	Transition from yellow to pale brown
12	600W	40s	26s	250ml+	Maximum shrinkage phase
13	600W	40s	24s	250ml+	Isolated, faint preliminary snap
14	600W	40s	31s	275ml-	Re-expansion turning point confirmed

Step 5 Interval Heat: 144k Ws / Cumulative Total: 313k Ws

Step 6: Thermal Adjustment Prior to First Crack

An additional set of 600W × 30s was introduced to prevent stalling upon entering first crack.

No.	Power	Exposure	Agitation Interval	Volume Trend	Operational Notes
15	600W	30s	29s	275ml+	Steady pre-crack expansion confirmed

Step 6 Interval Heat: 18k Ws / Cumulative Total: 331k Ws

Step 7: Driving First Crack (800W Boost)

No.	Power	Exposure	Agitation Interval	Volume Trend	Operational Notes
16	800W	20s	28s	275ml+	Quiet
17	600W	20s	29s	275ml+	Latent heat absorption
18	800W	20s	32s	300ml-	First crack commences (audible pops, expansion)
19	600W	20s	29s	300ml+	First crack fully develops

Because first crack developed with strong momentum, 800W bursts were terminated to prevent overshoot.
Step 7 Interval Heat: 56k Ws / Cumulative Total: 387k Ws

Step 8: Finishing & Termination Evaluation

No.	Power	Exposure	Agitation Interval	Volume Trend	Operational Notes
20	600W	20s	29s	300–325ml	First crack tapers off
21	600W	15s	24s	325ml	Calibration phase
22	600W	15s	24s	325ml+	Crease smoothing progressing well
23	600W	15s	25s	325ml+	Subtle indicators of second crack approaching
24	600W	10s	25s	-	Roast terminated (Target: Medium-Light)

Step 8 Interval Heat: 45k Ws / Cumulative Total: 432k Ws

Step 9: Discharge and Rapid Cooling

Discharged immediately onto the cooling tray; measured bean temperature and commenced forced air cooling.

Discharge Bean Temperature: 215.0°C
Total Post-Roast Weight: 119.2g (Net yield after 1.2g defect culling: 118.0g)

Roast Summary

Evaluation Metric	Measured Value
Total Steps	24 steps
Net Microwave Exposure Time	13 min 35 sec
Total Elapsed Time (incl. agitation)	24 min 20 sec
Discharge Bean Temperature	215.0°C
Finished Bean Weight	119.2g (82.8% of dry green weight)
Total Cumulative Energy	432k Ws
Time-Normalized Equivalent Energy	1065.21 kW/h

Ethiopia Shidama Baturo roast profile chart, 22 August 2026

Technical Analysis

Completing in 24 steps with a cumulative energy input of 432k Ws and a final drop temperature of 215.0°C exemplifies the ideal profile for an Ethiopian natural medium-light roast (retaining vibrant floral volatiles while avoiding astringent underdeveloped notes or excessive bitterness).

The time-normalized energy metric of 1065.21 kW/h demonstrates exceptional agreement with the empirical baseline benchmark (approx. 1,060 kW/h) established for 144g pre-hydrated green coffee batches.