Oatmeal is a popular ingredient in stouts and porters, and recently has even found it’s way into less traditional beers such as IPAs. While the flavor can be slight, oatmeal is used to give beer a velvety slickness and aid in head retention.
Oatmeal needs to be mashed in the presence of other grains, as it does not have the enzymes to convert on its own. This means that oats can not be steeped, and extract brewers will need to perform a mini mash if they want to use oatmeal in a recipe. Mashing oatmeal can cause it own problems. Oats contain a significant amount of beta-glucans that give oatmeal their signature gummy consistency. When used in the mash the beta-glucans can cause problems with sparging/lautering, resulting in a stuck mash. In fact, the only time in my life that I have had a stuck sparge was when brewing an oatmeal stout. To avoid this problem, I usually add a couple of scoops of rice hulls into my mash. The rice hulls act as filter media, which helps prevent a stuck sparge. If you are using a large proportion of oatmeal (greater than 20% of the total grain bill) a step mash may be necessary. Resting the mash between 100°F -110°F, for twenty minutes will help break down the beta-glucans.
Oatmeal has its greatest impact in the mouthfeel of the beer, helping create a smooth and silky texture. Oats also contain a large amount of oils (lipids) which can add an oily texture to the beer as well. Despite the presence of oils in the grain, which you would expect to negatively impact head retention, oatmeal helps build a nice creamy long lasting head. There is some speculation that the high protein content of the oats promotes head retention, overcoming any negative effect from the oil content. Although the high protein content can aid in head retention, it is also likely to result in beer haze which is not overly important when brewing stouts, but something to keep in mind if you want to try oats in a lighter colored beer.
The flavor of oatmeal can be subtle, and in bold flavored stouts, can be completely non-existent. To increase the flavor contribution of oatmeal, bake the oats in an oven at 300°F. Carefully turn the oats and allow them to brown, but don’t let them burn. They are ready when they start to smell like fresh oatmeal cookies.
I hope this information proves useful to you. If you ever have any questions on this or any other topic related to brewing, please feel free to contact me at email@example.com. You can also follow me on twitter @craftedbarley.