How Do Grains Affect Beer Flavor? While brewers tend to focus heavily on the brewing process and fermentation, a lot of a beer’s flavor comes from decisions you make before you can even start brewing. The choice of grains in a beer composition gives it most of its flavor, so its really important to know what certain grains will do to change the way beer tastes. We’ll explore how the grain bill affects beer flavor here to give you more insight when conceptualizing new brews.