THE SHORT ANSWER
Decaffeination removes most caffeine from green coffee before roasting. Different processes use water-based systems, carbon dioxide or approved solvents. Decaf is not necessarily caffeine-free, and the method should be checked on the specific product.
One process, explained clearly
Swiss Water describes a process in which hydrated green beans meet green coffee extract, caffeine migrates out, and carbon filtration removes caffeine from that extract. The beans are then dried for later roasting. That is one branded method, not the description of every decaf on the shelf.
Ask a better shopping question
Instead of treating decaf as a single flavour, ask about the origin, roast, decaffeination method and brewing recommendation. Do not assume a product uses Swiss Water unless its packaging or seller confirms it. The process name belongs to the actual supply chain, not to a general promise of smoothness.
Brew for enjoyment
Start with your usual method and adjust by taste. If your new bag drains faster or tastes different, keep the dose constant and change the grind a little at a time. An evening coffee can still be a proper ritual: warm the mug, put on the music and give the brew your attention. For strict caffeine requirements, seek product-specific information rather than relying on the word decaf.
Change one thing, taste, and keep a short note. A recipe becomes useful when you can repeat the cup you enjoy.
Try it for yourself
Sources & further reading
Source links support the factual context. Our home recipes and tasting suggestions are identified as starting points.