Roasting Decaf Coffee

Roasting Decaf Coffee

Roasting decaf coffee is a unique challenge. Many of the rules of thumb that apply to regular coffees do not hold when roasting decaffeinated beans. Through our participation in James Hoffmann’s Decaf Project, we gained valuable insights into how different decaffeination methods affect green coffee and what that means for the coffee roaster.

Here are some of the key challenges with roasting decaf coffee:

  • Colour: Decaf coffee starts off darker in its green state, meaning the roasted coffee will often appear darker than it tastes. Relying solely on visual cues for roast level can be misleading.
  • First Crack: Decaf coffee often has a muted or entirely inaudible first crack, making it difficult to mark the crack and calculate development time accurately.
  • Development Time Ratio: The common rule of thumb for regular coffee—20-25% development time—is difficult to calculate and less applicable for decafs due to their altered physical properties.

Without the usual markers to guide the roast, roasters must return to the fundamentals: roasting-tasting, adjusting, and re-tasting. The process becomes one of trial, refinement, and careful observation.

Typically, decaf coffee requires less energy during roasting due to its weakened cellular structure, which results from the decaffeination process. Roasters also tend to roast decaf to a lower final temperature to prevent scorching the more fragile beans.

The Decaf Project

James Hoffmann’s Decaf Project provided an excellent opportunity to explore the intricacies of roasting decaf coffee. The project centered on one coffee, La Virgen, a washed coffee from Huila, Colombia. This single lot was divided into four parts, each sent for a different decaffeination method:

  • CO₂ decaffeination
  • Ethyl Acetate (EA) decaffeination
  • Swiss Water decaffeination

The decaffeinated coffees were then returned to participating roasters and sold to customers as tasting kits, allowing coffee enthusiasts to explore how each decaffeination process impacted flavour and body.

This project gave us the rare opportunity to compare decaf coffees side-by-side while collaborating with roasters worldwide to share data, techniques, and insights.

Visual Appearance

Decaffeination significantly alters the appearance of green coffee. All decafs were noticeably darker than the original coffee.

  • The CO₂ decaf beans were a deep green colour and visually uniform.
  • The EA decaf beans had a darker yellow hue.
  • The Swiss Water decaf was similar to the CO₂ decaf but lacked the green tinge, appearing slightly duller.

These differences reflect how each decaffeination method interacts with the beans, leaving distinct visual markers.

Moisture Content and Density

Decaffeination affects the physical properties of the beans, including moisture content and density. The final stage of each decaffeination process is to dry the coffee back to a stable moisture content. Each process produced coffees with a different final moisture content. All decafs had higher moisture content than the original coffee.

    • CO₂: 12.9%
    • EA: 13.7%
    • Swiss Water: 11.4%
    • Original Coffee: 10.5%

The EA decaf had the highest moisture content with the Swiss Water decaf was closest to the original coffee.

  • Density: The CO₂ decaf was the only one measured as denser than the original coffee, possibly due to the high-pressure processing environment and gentle drying process.
    • CO₂: 860 g/L
    • EA: 785 g/L
    • Swiss Water: 820 g/L
    • Original Coffee: 830 g/L

The higher density of the CO₂ decaf suggests it retained more of its structural integrity during processing, whereas EA and Swiss Water processes seemed to reduce density.

Ikawa Sample Roasts

To begin, we roasted all three decafs using the same sample roast profile on our Ikawa Pro 100 sample roaster. This allowed us to cup the coffees and observe how they behaved under identical roasting conditions.

We used an outlet air profile, where the roaster adjusts inlet air to match the desired outlet air curve.

Observations:

  1. First Crack:
    • The EA process decaf had an audible first crack, while the CO₂ and Swiss Water decafs did not. This made it easier to track the EA roast but required a more intuitive approach for the other two.
  2. Energy Input:
    • The EA and CO₂ decafs required more energy to achieve the same outlet air curve than the Swiss Water decaf.
    • This was particularly evident during the Maillard phase, where sugars caramelize and flavor develops.
    • The EA decaf required the most energy, reflecting its higher moisture content.

Production Roasts

For production roasting, our goal was to roast all coffees to a comparable medium roast level, ensuring the differences in flavour came from the decaffeination process rather than the roast profile.

The decafs all started at different colour levels, so matching final colour across all coffees would result in uneven roast levels. Instead, we focused on using similar profiles and matching acidity rather than relying on colour as a guide. The CO₂ and EA decafs, with higher moisture content, required additional energy during the middle phase of the roast to maintain momentum. We used the same base profile for all three coffees but made adjustments:

  • For the CO₂ and EA decafs, we increased energy during the middle phase to bring them to first crack in good time.
  • We then roasted all the decafs to the same final temperature in a similar roast time.

On the cupping table, the coffees had similar acidity levels and balance. Each decaf had its unique character, but all were medium roasts we would be proud to serve to customers.

While we aimed for consistency in roast level, the flavour profiles highlighted the impact of decaffeination. Overall we were impressed that all the decafs retained the character of the original coffee, with subtle differences. We will discuss what we observed in the cup in another article.

Final Reflections

The Decaf Project was a fascinating experiment, offering insights into the complexities of roasting decaf coffee.

Decaf roasting is a constant learning process—one where experimentation and trusting your palate are key. We are grateful to the roasters who shared their data and expertise through The Decaf Project’s Discord chat, as well as to the customers who took part in tasting these coffees.

It should be noted that the observations shared here apply specifically to the Decaf Project coffees.

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