Dark Roasts coffees are roasted approximately 30 min, have a dark oily surface with a smokey, bitter taste. Dark roasts are a popular choice for espresso, Turkish and Greek coffee drinks.Darker roasts also carry more of the compound called N-methylpyridinium, which has been shown in research to reduce stomach acid in tests subjects. For this reason, dark roasts are recommended for those with sensitive stomachs. Although darker roasts produce a more bitter, strong taste, they typically are lower in caffeine content than lighter roasts. This is due to more caffeine being naturally removed in the longer roasting process.