Freshly roasted coffee keeps releasing CO₂ for days after roasting, a process called degassing. A short rest lets those gases settle so the flavours read clearly in the cup. These are guidelines, not rules. Taste as you go and brew whenever it suits you.
Espresso
Rest 2+ weeks
Best within 6 weeks
Filter
Rest 3+ weeks
Best within 8 weeks
Once opened, every reseal lets fresh oxygen in, which speeds up staling. Aim to finish an open bag within a month, and press out as much air as you can before resealing.
Roast level matters too: lighter roasts are denser and degas more slowly, while darker roasts release gas faster. Your own palate is always the final guide.