If you're trying to DIY iced coffee at home, don't start with regular brewed coffee. Ordinary coffee brewed with hot water releases acids and oils that can make your iced coffee taste bitter. Instead, start with cold brew coffee concentrate, which is super easy to make at home: just coarsely ground coffee beans and water left to steep overnight. For the ultimate iced coffee, pour the concentrate over ice with a little water and a little liquid syrup—either agave, simple syrup (a heated combo of sugar and water), or your favorite flavored coffee syrup, if you want to add a touch of vanilla or hazelnut flavor to your iced coffee recipe. Then top it off with a little half-and-half for the perfect iced coffee at home.