1. Technical Overview

Coffee with 97% caffeine removed is the FDA’s definition of decaffeinated coffee [1]. Ludwig Roselius, the chief of Kaffee HAG, developed the first practical decaffeination process in 1903 [2].

Figure 1: Coffee and tea are popular drinks worldwide
Image credits: Soner Kose at Pixabay

Supercritical carbon dioxide (sCO2) has decaffeinated coffee since the 1970s. The process employs ethanol or water as a co-solvent to contradict the low solubility of caffeine in sCO2. Green coffee beans are soaked in hot water inside a sealed extraction container till they are 50% saturated with water to bring out the caffeine [3].

Next, sCO2 is pumped into the container at high pressure. This dissolves caffeine in sCO2. Thereafter, sCO2 is moved in a low pressure vessel. The sCO2evaporates leaving caffeine behind [3].

Methods to decaffeinate coffee are [4]:

  • Carbon dioxide Supercritical Fluid Extraction (CO2 SCFE)
  • Swiss Water Process
  • Ethyl Acetate Decaffeination
  • Methylene Chloride Decaffeination

Tea is decaffeinated using [5]:

  • CO2 SCFE
  • Ethyl Acetate Decaffeination
  • Methylene Chloride Decaffeination

2. Chemistry of Caffeine & the Decaf Coffee-Tea Markets

2.1. Why Tea & Coffee Make Us Feel Better?

Caffeine is C8H10N4O2 with the systematic name 3,7-dihydro-1, 3,7-trimethyl-1H-purine-2, 6-dione. Its structure is similar to that of adenosine, the hormone that slows down the body. Caffeine blocks adenosine flow and thereby stimulates the body by lowering fatigue and boosting concentration. Excessive consumption, however, invites nervousness, insomnia, mood swings, and hostility [3].

2.2. Decaf Coffee & Tea Markets

Surging awareness on health issues caused by large caffeine intake is expected to expand the worldwide decaffeinated (decaf) coffee market at a 6.9% CAGR from 2019 and reach $21.45 billion by 2025 [6]. Prospects for the decaf tea industry are similarly bright.

Salaried millennials living in cities are the main customers for decaf coffee. Key drivers are [6]:

  • Rising awareness on the negative health effects of excessive caffeine consumption such as blood pressure, discomfort, anxiety etc.
  • Increasing coffee intake across the globe

With greater awareness on the health positives of decaf tea, its consumption is picking up across the world. Main drivers include:

  • Global customers taking cognizance of the health benefits of antioxidant-rich decaf tea.
  • Innovations: Tetley has developed “Sleep Easy” tea bags with lavender and vanilla, which stimulate sleep.
  • Sedentary lifestyles demand a shift towards more healthy and natural products.
  • Surging number of decaf tea producers in developing countries [5].

3. Supercritical Fluid Extraction (SCFE) & Carbon dioxide (CO2) SCFE

3.1. Why SCFE Use is Rising?

Regulations on toxicity, quality, safety, and residues in consumer products are getting stricter as consumers demand products with more natural ingredients in food-beverage, pharmaceutical, neutraceutical, and personal care products. SCFE is safer, more eco-friendly, and leaves behind zero or less toxic residues in the final product.

Alternative methods have drawbacks:

  • Solvent Extraction: uses toxic organic solvents whose residue cannot be completely separated from the extracted ingredient [7]. Some solvents deplete the ozone layer and create environmental issues [8].
  • Hydrodistillation: employs heat which can thermally degrade the ingredient [9].

3.2. What are Supercritical Fluids & How do they Assist with Extraction?

A fluid at above its critical pressure and temperature is a supercritical fluid. The phase boundary between its liquid and vapour phase disappears and its properties can be customized by changing the pressure and temperature.

Roughly, supercritical fluids with higher density possess greater solvent power. And because altering pressure and temperature substantially varies their density, supercritical fluids make exceptional solvents.

Figure 2. Triple Point Parameters

Supercritical fluids are excellent solvents because of their [10]:

  • Higher, Liquid-like Density: boosts solvent power.
  • Low, Gas-like Viscosity: improves mass transfer and diffusion inside porous solids.
  • Low, Gas-like Surface Tension: enables greater seepage inside porous solids.

3.3. Why Supercritical Carbon dioxide (CO2) Makes an Excellent SCFE Solvent?

Carbon dioxide and water are the most popularly utilized supercritical fluids [11]. Supercritical (CO2) is an ideal solvent for SCFE because it [10]:

  • Has a critical temperature of 31.10C, which is around the ambient temperature. Relatively low temperatures for CO2 SCFE avoid thermal degradation.
  • Has a more manageable critical pressure of 73.9 bar.
  • Is non-flammable and non-toxic.
  • Has a customizable density to upgrade its solvent power.
  • Is available in ample quantities and in pure form.
  • Has a comparatively low cost.

Although CO2 is a greenhouse gas (GHG), the SCFE process using CO2 becomes eco-friendly if the gas is captured from the atmosphere, reused, and recycled.



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  1. What is Decaffeination? Dr. Ananya Mandal. News Medical.
  2. How do You Decaffeinate Coffee. Stephen Dowling. BBC.
  3. Understanding Decaffeination Processes. Future Learn.
  4. How is Coffee Decaffeinated? 4 Safe Methods. Little Coffee Place.
  5. Decaffeinated Tea Market. Fortune Business Insights.
  6. Global Decaf Coffee Market – Forecast till 2025. Market Research Future.
  7. Fires and Explosions. Max Houck et al. Fundamentals of Forensic Science (Third Edition). Science Direct.
  8. Initial Considerations. Francisco Pena-Pereira et al. The Applications of Green Solvents in Separation Process. Science Direct.
  9. Supercritical Fluid Extraction. E. Reverchon. Encyclopedia of Food Sciences and Nutrition (Second Edition). Science Direct.
  10. Supercritical CO2: A Green Solvent. Chemical Engineering.
  11. Supercritical Fluids. LibreTexts.