Coffee Roaster: Temperature Profile Controller Build

India produces world-class coffee beans (Coorg, Chikmagalur, Wayanad), and home roasting brings out flavours that pre-roasted beans lose within weeks. A DIY coffee roaster with a temperature profile controller lets you precisely control the roast from light to dark, developing complex flavours. This guide covers building a profile-controlled roaster for under ₹3,000.

Why Build a Coffee Roaster?

Green coffee beans undergo dramatic chemical changes during roasting. The temperature profile — how fast temperature rises, where it pauses, and when key events occur — determines the final flavour:

• Drying phase (25-170°C): Moisture evaporates, beans turn yellow. 4-6 minutes.
• Maillard reaction (170-200°C): Browning, flavour development. Sugar caramelisation begins.
• First crack (~200-210°C): Beans crack audibly (like popcorn). Light roast complete. Bright, acidic flavours.
• Development (210-225°C): Sugars caramelise further. Medium roast territory. Balanced flavour.
• Second crack (~225-230°C): Oils appear on surface. Dark roast. Bold, smoky, low acidity.

Roasting Temperature Profiles

A typical 12-minute medium roast profile:

• 0-4 min: Charge at 200°C, temperature drops to 150°C (thermal mass of beans), then recovers
• 4-8 min: Steady climb at 10-15°C/minute
• 8-10 min: First crack at ~200-210°C. Reduce heat to slow the roast.
• 10-12 min: Development time. Control ramp rate to 5-8°C/minute.
• 12 min: Drop at 215-220°C for a medium roast. Cool rapidly.

Components for the Build

• Roasting chamber: modified popcorn popper (₹500-1,000), heat gun + dog bowl, or bread machine drum
• K-type thermocouple + MAX6675 (₹229) for bean temperature
• Arduino Mega for profile logging and control
• SSR 25A for heater control
• Fan/blower for airflow and cooling (12V blower fan)
• Optional: second thermocouple for air/environment temperature
• Serial connection to laptop for real-time graphing (Artisan roasting software)

Thermocouple Placement

Two thermocouples are ideal:

• Bean temperature (BT): Probe inserted into the bean mass. This is the primary control measurement. Place the tip in the centre of the bean pile.
• Environment temperature (ET): Probe in the air above the beans. Shows the air temperature entering the bean mass. Useful for understanding heat transfer.

Both connect via MAX6675 modules to separate Arduino SPI pins. The Arduino logs both temperatures at 1-second intervals and transmits to the Artisan roasting software via serial for real-time graphing.

PID Profile Controller

Unlike simple thermostats, a coffee roaster needs rate-of-rise (RoR) control — not just target temperature but how fast you are getting there. The Arduino calculates RoR (°C/minute) from consecutive temperature readings and adjusts heater power to maintain the desired ramp rate.

Profile segments define target RoR values rather than target temperatures. This gives the roaster control over flavour development that simple temperature targeting cannot achieve.

Airflow and Chaff Management

Roasting produces chaff (thin skin from the bean) that must be removed to prevent burning. A blower fan through the roasting chamber carries chaff out into a collection basket. The same fan provides convective heat transfer for even roasting.

After roasting, rapid cooling is essential — dump beans into a colander with a fan blowing through them. Cool from roasting temperature to room temperature in under 3 minutes to stop the roast development.

Recommended Components

Roasting Tips for Indian Coffee

• Indian single-origin beans: Coorg Arabica, Chikmagalur plantation, Wayanad Robusta — all excellent for home roasting. Buy green beans from speciality roasters or directly from estates.
• Start light: Indian Arabica beans shine at light to medium roast (City to Full City). Dark roasting destroys the delicate floral and fruity notes.
• Rest period: After roasting, rest beans for 24-72 hours before brewing. This allows CO2 to degas and flavours to settle.
• Log everything: Use Artisan software to graph every roast. Compare profiles to find what works best for each bean origin.
• Ventilate: Roasting produces significant smoke, especially past first crack. Roast outdoors, under an exhaust hood, or near an open window.