Decaf is short for decaffeinated coffee.
It is coffee from coffee beans that have had at least 97% of their caffeine removed.
There are many ways to remove caffeine from coffee beans. Most of them include water, organic solvents or carbon dioxide.
Coffee beans are washed in the solvent until the caffeine has been extracted into it, then the solvent is removed.
The beans are decaffeinated before they are roasted and ground. The nutritional value of decaf coffee should be almost identical to regular coffee, apart from the caffeine content.
However, the taste and smell may become a little milder and the color may change, depending on the method used.
This can make decaf coffee more pleasing to those who are sensitive to the bitter taste and smell of regular coffee.
In summary, Decaf Coffee beans are washed in solvents to remove 97% of the caffeine content prior to roasting. Aside from the caffeine, the nutritional value of decaf coffee should be almost identical to that of regular coffee. (Source: Healthline.com)