Why is it not recommended to drink coffee immediately after it's roasted? The rule of thumb is that you first drink coffee approximately 3 days after it is roasted, but what is the exact reason for this?
Fresh off the roast, coffee has high levels of carbon dioxide and nitrogen (based?) gasses. These gasses will greatly contribute to retro-nasal activity as well as initial flavors (think carbonated water). The most apparent flavor one gets from this is metallic. At my work, 4 days is considered minimum for serving and tasting, although there's always exceptions.