title_body: Ideal brewing time for 3-cup Chemex?
upvoted_answer: Ideal brewing time varies based on grind. Finer grinds need shorter brew times. Coarser grinds need longer brew times. This is because fine grinds expose more surface area of the beans, which lets solutes diffuse quickly into the water. Coarse grinds need more time for solutes to be drawn out.
  As for roast level, that's totally up to you. Different roast levels expose different flavor profiles, so you might like them all brewed for the same amount of time or you might prefer to brew darker or lighter roasts for longer or shorter times. There's not really an ideal here unless you align with the preferences of the person offering you the ideal.
  You'll know that your brew time is too long if your coffee tastes bitter. Coffee brewed perfectly should taste very smooth if you're using medium or lighter roasts. Very dark coffees might taste bitter in a burnt sort of way even with perfect brewing. Conversely, too short brew time will result in weak tasting coffee. Note that weak coffee can also be caused by too high of a water to grounds ratio or poor contact between water and grinds (channeling during the pour). Bloom to help mitigate channeling.
  Hope this info helps!