There are various ways to remove caffeine from the coffee beans. The method usually involves water, organic solvents, or carbon dioxide. And the process of decaffeination commonly begins by immersing beans in a solvent which extracts the caffeine.
An alternative approach, uses carbon dioxide or a charcoal filter. This is known as the Swiss Water Process for caffeine removal.
Decaffeination always occurs before the beans undergo roasting and grinding. So afterwards, decaf beans resemble regular coffee, but with lower caffeine levels.
Another concequence of the decaffeination process is that the taste and aroma of the coffee might become milder. This makes decaf a more appealing option for those who dislike the bitterness and strength of regular coffee.