Oatmeal stout is my favorite style under the category of stout. If you want to get technical about it all stouts come from the mother style: porter.
Oatmeal stout was actually a dead style for a number of years in England. The famous beer writer Michael Jackson lamented the loss in his book The World Guide to Beer. The owner of Merchant Du Vin (Charles Finkel) had Samuel Smith brew one. That beer relaunched interest in the style and now they are a very popular style among American craft breweries and brewpubs.
Oatmeal stouts are most often easy on the ABV ranging from 4% to 6%. The addition of the oats gives the beer a much fuller mouthfeel that is silky smooth and a little sweet from the oat addition.
Here are things that you are going to get in the style:
Eyes: Oatmeal stouts will with be very dark brown to almost black in color. They will usually have a massive cap of foam on them from a non-aggressive pour that will range from off-white to tan in color.
Nose: The main player in this beer is going to be the roasted grain smell. This should be upfront and should be pleasant, but not overpowering. Other flavors can range from coffee, toffee, and in rare instances even dark fruit. Traditional standards would have the dark fruits as unwanted, but if it tastes good then drink it. The grains used for oatmeal stouts can use pale malt, crystal malt, chocolate malt, black patent malt, roasted barley, and 5 to 15% oatmeal in the mash to give it the name. The style can have up to 30% oatmeal addition, but if you have ever homebrewed an oatmeal stout I can't imagine the mess that would make with that high of an addition of oats. Hops traditionally are only used for bittering, but some American brewers are a little heavy handed and may exhibit hop aroma if that is the brewers intention.
Mouth: This is where oatmeal stouts shine. The mouth will be full, silky, creamy, and smooth.
Overall: Oatmeal stouts will be roasty, filling, slightly sweet, and satisfying
Commercial Examples: Samuel Smith's Oatmeal Stout, Goose Island Oatmeal Stout, Rogue Shakespeare Stout, Velvet Merlin-Firestone Walker Brewing
Local Examples: Barley Island-Brass Knuckles, Lafayette Brewing Company-Black Angus Oatmeal Stout, Zaius - Sun King Brewing Company
Also, if anyone from Three Floyd's reads this blog please bring back the greatest oatmeal stout of them all: Hell's Black Intelligencer.