How long before brewed coffee loses its flavor?

According to Food and Wine magazine's Ray Isle, after 45 minutes, the heating apparatus will start to cook the coffee, turning it bitter-tasting. Other answers vary; there are those who say no more than 20 minutes, and those who will give it as much as a half hour, but basically, we're talking about a pretty small window for ideal-tasting coffee once it's been brewed (and don't even think of reheating it!), so don't brew more than you're going to drink.
 
Source(s):
CBS News, The Early Show: "Brew Perfect Coffee at Home, for Pennies"