Oatmeal stouts typically lack hop aroma and flavor.
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Oatmeal stouts have some form of oats as 5% to 8% of the grain bill. The easiest forms to use are flaked oats or malted oats. These can be added directly to the mash. Rolled oats and instant oats must be cooked before mashing (15 minutes above 190F/88C; Grant, 2007). Be careful to avoid flavored breakfast oat meals.
Many recipes suggest toasting the oats lightly before mashing to enhance an oatmeal cookie flavor. Bake the oats at 300F (149C) to 325F (163C) for a few minutes. Remove them from the oven when they give off a toasted cookie smell (Grant, 2007).
Oats have no enzymes, so these must be mashed (Galante, 1997). Extract brewers will need to perform a small partial mash with the oats before adding it to the main boil.
The specialty malts are usually a combination of chocolate malt, roasted barley, or black malt for 4% to 8% of the total gravity points. The percentage of roasted malts is similar to other porter or stout beer styles. Medium to slightly dark crystal malts (5%) are also common. Zainasheff (2013) likes adding Victory malt. The base malt is usually a British pale ale malt like Maris Otter.
British hops like Kent Goldings, Fuggle, and Target are recommended. Neutral bittering hops will also work. A single hop addition for bittering is sufficient.
For yeast, choose Irish or British ale yeasts that are moderately attenuative. The reviewed recipes suggest English Ale, London ESB, London Ale, or Irish ale.
A challenge is that oats can form a gummy mass, increasing the risk for a stuck sparge. Adding rice hulls (5%) can promote drainage. Quick oats are finely milled and sticker than other forms. Limiting the overall percentage of oats from 5% to 10% will also help avoid lautering problems (Grant, 2007). Recipes with a high percentage of oats (more than 25%) and/or unmalted oats can benefit from a step mash that begins at 113F (45C) for the enzyme beta glucanase (Grant, 2007).
A second technical challenge is that roasted malts are acidic, which could potentially lead to a mash pH that is too low. The brewing water may need to be slightly alkaline to counteract the acidity.
A perceptual challenge is achieving a medium body: Between a dry stout and a sweet stout.
Dornbusch, H. (2002). Oatmeal stout: Style profile. BYO.
Galante, S. (1997, October). Oatmeal stout: Style. BYO.
Grant, K. (2007, March-April). Cookie in a glass. BYO, 26-31.
Szamatulski, T., and Szamatulski, M. (1998). Clonebrews. Storey Books, North Adams, Massachusetts, 106.
Zainasheff, J. (2013, March-April). Oatmeal stout: Smooth and silky BYO, 19-23.
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