Decaffeinated Coffee Processing Methods? What is Supercritical Carbon Dioxide Processing for Decaf Coffee?

FrontStreet Coffee Briefs on Supercritical Carbon Dioxide Processing for Decaffeinated Coffee

The decaffeination process must be conducted while the coffee beans are still in their raw, green state. Currently, there are three main methods for removing caffeine: the traditional/European Process, Swiss Water Process (SWP), and Supercritical Carbon Dioxide Process (CO₂ Process). All three methods can effectively remove most of the caffeine, leaving only 2-3% of the original caffeine content in the coffee beans. Today, FrontStreet Coffee will focus on introducing the supercritical carbon dioxide processing method for decaffeinated coffee.

This method utilizes two natural elements—pure water and carbon dioxide (which we commonly refer to as soda water when combined)—to extract caffeine from green coffee beans. The inventor of this method is Kurt Zosel.

The Science Behind Supercritical CO₂ Extraction

In chemistry, this is known as supercritical CO₂ extraction technology. Supercritical carbon dioxide (hereafter referred to as SC-CO₂) has a density several hundred times that of gas and approaches that of liquid, yet its viscosity is similar to gaseous carbon dioxide. Its diffusion coefficient is approximately one-hundredth that of gas but several hundred times greater than that of liquid. Therefore, mass transfer or distribution processes occur much faster than in liquid solvents.

Why This Method Was Developed

This method was developed as a means of extracting caffeine from coffee beans due to the following characteristics:

1. Carbon dioxide has a critical temperature of 31.1°C and a critical pressure of 73 atmospheres (Atm). Due to its relatively close-to-room-temperature critical point, it is suitable for extracting heat-unstable substances. This has excellent effects on preserving the aromatic compounds in coffee.

2. Carbon dioxide is an inert gas—non-flammable, non-reactive, and leaves no residue. It is harmless to humans and does not cause environmental pollution.

3. High-purity carbon dioxide is easy to produce and inexpensive.

The Extraction Process

The supercritical CO₂ caffeine extraction method involves allowing coffee beans to absorb moisture and expand to twice their original size, which loosens the caffeine molecules within the beans. Carbon dioxide is then added and subjected to pressure greater than 100 atmospheres (Atm) in water, creating a soda water environment. Carbon dioxide acts like a magnet, attracting caffeine molecules. Once captured by carbon dioxide, the caffeine begins to move. Carbon dioxide is highly selective—it does not capture the carbohydrates and proteins in coffee beans, as these are the main components responsible for coffee's flavor and aroma. After extraction is complete, the beans are naturally dried. The caffeine-containing water can easily be separated to extract caffeine for other commercial uses.

Advantages of This Method

1. Highly efficient caffeine extraction with no chemical contamination.

2. No chemical reactions occur with the carbohydrates and proteins in coffee beans.

3. Its byproduct (caffeine) is natural and 100% recyclable.

Important Notice :

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