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How is coffee decaffeinated?

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Quick answer

Decaf starts as green, unroasted coffee beans that are soaked or steamed so caffeine can move out. The caffeine is then drawn away by water passed through carbon filters, a food-grade solvent such as ethyl acetate, or supercritical carbon dioxide. The beans are dried and roasted, keeping most of their flavour.

Coffee is decaffeinated by soaking or steaming unroasted green beans and then washing the caffeine out with water, a solvent such as ethyl acetate, or pressurised carbon dioxide. The beans are dried and roasted afterwards, keeping most of their flavour compounds while losing about 97 percent or more of the caffeine.

Step by step

  1. Green coffee beans are steamed or soaked in water, which swells them and loosens the caffeine inside their cells.
  2. A solvent, water extract or pressurised carbon dioxide is circulated through the beans to pull dissolved caffeine out.
  3. The caffeine-rich liquid is drained away, and the caffeine is separated from it using filters, evaporation or recovery equipment.
  4. The beans are rinsed or steamed again to remove any remaining solvent and are then dried back to their normal moisture.
  5. Finally the decaffeinated green beans are roasted just like regular coffee, developing their colour and aroma.

Key things to understand

  1. Decaffeination is done on green, unroasted beans, because roasting would lock in flavour and make extraction uneven.
  2. Steaming or soaking swells the beans and frees caffeine so it can move out of the cells into a liquid.
  3. Solvent methods use dichloromethane or ethyl acetate, which dissolve caffeine far more readily than most flavour compounds.
  4. Water-only processes use a flavour-saturated green coffee extract so caffeine diffuses out while flavour molecules stay in the bean.
  5. Carbon dioxide held above its critical pressure acts like a solvent that seeps into beans and carries caffeine away.

Labelled diagram

  1. Green beans

    Unroasted beans are steamed or soaked to swell them and free caffeine.

  2. Extraction

    Solvent, flavour-saturated water or supercritical carbon dioxide draws caffeine out of the beans.

  3. Separation

    Caffeine is removed from the liquid by filters or recovery equipment for reuse.

  4. Drying

    Beans are rinsed, steamed and dried to remove leftover solvent and water.

  5. Roasting

    Decaffeinated beans are roasted, developing the familiar brown colour and coffee aroma.

Taking caffeine out of green coffee beans

Real-world examples

  • Decaf labelled as water-processed has had its caffeine removed with water and activated carbon filters, with no chemical solvent.
  • Beans described as naturally decaffeinated often used ethyl acetate, a compound also found in ripening fruit.
  • Large industrial plants use supercritical carbon dioxide to decaffeinate tonnes of green beans in big pressure vessels.
  • A filter-coffee drinker in Chennai can buy decaf South Indian coffee powder to enjoy an evening tumbler without much caffeine.

Common mistake

✗ Myth: Decaf coffee is made by removing caffeine from brewed coffee after it is made.

✓ Fact: Caffeine is removed from the raw green beans before roasting. Treating brewed coffee would strip its flavour, so the process works on the beans, which are then roasted and brewed as usual.

People also ask

How much caffeine is in decaf coffee?
A typical cup of decaf contains only a few milligrams of caffeine, often somewhere between about 2 and 15 milligrams depending on the beans, the method and the cup size. Regular brewed coffee usually has around 80 to 100 milligrams, so decaf cuts caffeine sharply without removing it completely.
What is the swiss water process for decaf?
It is a solvent-free method that uses only water and carbon filters. Green beans are soaked in a green coffee extract already saturated with flavour compounds, so only caffeine diffuses out of them. Activated carbon then traps the caffeine from the extract, which is reused for the next batch of beans.
Is decaf coffee bad for you?
For most people decaf is considered safe and is a common choice for those limiting caffeine. Solvent residues are kept within strict food-safety limits, and roasting removes most traces. It still contains small amounts of caffeine and is acidic, so anyone told by a doctor to avoid coffee should check first.
Is decaf completely caffeine-free?
No. Decaffeination removes most but not all caffeine, typically 97 percent or more. A cup of decaf usually still holds a few milligrams, compared with roughly 80 to 100 milligrams in a regular cup of brewed coffee.
Are chemical solvents left in decaf coffee?
Only trace amounts at most. The beans are steamed and rinsed after extraction to drive off solvent, and roasting at around 200 °C evaporates what remains. Food regulators set strict residue limits that decaf must meet.
Why does decaf sometimes taste weaker?
Some flavour and aroma compounds leave the beans along with the caffeine, and the soaking and drying can change the bean's structure. Caffeine itself also adds bitterness, so removing it slightly softens the taste.
What happens to the caffeine that is removed?
In many plants the caffeine is recovered from the solvent or carbon filters, purified and sold. It ends up in soft drinks, energy drinks and medicines, so decaffeination also supplies the caffeine industry.

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