Rye flakes are unlike typical flaked ingredients in that they are added purely for their spicy flavor and do little to add body and mouthfeel. 5-10% is all you need to add a distinct rye flavor to your malt profile, and you can increase from there depending on your desired taste or the style you're brewing. A staple ingredient in German Roggenbier, Finish Sahti, and American Rye-P-As.