Decaffeination happens to green, unroasted coffee beans, before any roasting or brewing decisions get made, and it is a genuinely involved process rather than a different type of coffee plant. Roast level, discussed in our roast levels guide, is an entirely separate decision made afterward, decaf can be roasted light, medium, or dark just like regular coffee.
The most common method today is the Swiss Water Process, which uses only water, temperature, and time, no chemical solvents at all. Green beans are soaked in hot water to dissolve out the caffeine along with other flavor compounds, then that water is passed through an activated carbon filter that is calibrated to trap caffeine molecules while letting the flavor compounds pass through. The resulting "flavor-charged" water is then used to soak fresh batches of beans, and because the water is already saturated with everything except caffeine, only caffeine diffuses out of the new beans this time, preserving most of their original flavor.
Solvent-based methods are older and still widely used, particularly the methylene chloride process and the ethyl acetate process, the latter sometimes marketed as "naturally decaffeinated" since ethyl acetate occurs naturally in some fruits, even though the industrial version used is typically synthetic. Both work by exposing steamed, moistened beans directly to the solvent, or indirectly through a water bath the solvent is later used to strip caffeine from, then rinsing and drying the beans before roasting. Regulatory agencies including the FDA have long considered the trace residual solvent levels left in the finished bean safe, though the Swiss Water and CO2 methods appeal to people who would rather avoid the question entirely.
A newer method uses supercritical carbon dioxide, CO2 pressurized and heated until it behaves like both a liquid and a gas at once, which is then passed through moistened beans to selectively pull out caffeine molecules. It is more expensive to run than the other methods, which is why it shows up more often in larger commercial decaf production than in small-batch roasting.
None of these methods remove 100 percent of the caffeine, and this is the part most people get wrong. According to the Mayo Clinic's caffeine reference chart, an 8-ounce cup of brewed decaf coffee still contains roughly 2 milligrams of caffeine, a small enough amount that it is genuinely fine for the vast majority of caffeine-sensitive people, but not technically zero. If you are avoiding caffeine for a medical reason rather than just personal preference, that distinction is worth knowing rather than assuming decaf means none at all.
Flavor is the other honest tradeoff worth naming. Even the gentlest decaffeination methods remove or alter some of the compounds responsible for a coffee's fuller flavor, which is part of why decaf has a reputation, not entirely undeserved, for tasting flatter or thinner than the same bean would have tasted with its caffeine intact. Quality varies a lot by roaster here, a specialty shop using a good bean and a Swiss Water process will taste meaningfully better than a generic commercial decaf, so it is worth trying a few different sources before deciding you simply do not like decaf. Perfect Daily Grind has a good piece on what is and is not true about decaf if you want to dig further.
If you are cutting back on caffeine for sleep reasons specifically rather than avoiding it entirely, decaf in the afternoon or evening is a genuinely reasonable middle ground, letting you keep the ritual and most of the flavor while removing the part that would actually keep you up. For more on timing caffeine around sleep, see our guide on when to stop drinking coffee. Home Barista Corner is worth a look if you want to see how decaf performs on a home espresso setup before switching.