Stout is a dark beer made using roasted malt or roasted barley, hops, water and yeast. Stouts are traditionally the generic term for the strongest or stoutest porters, typically 7% or 8%, produced by a brewery.The first known use of the word stout for beer was in a document dated 1677 found in the Egerton Manuscript, the sense being that a stout beer was a strong beer not a dark beer. The name porter was first used in 1721 to describe a dark brown beer that had been made with roasted malts. Because of the huge popularity of porters, brewers made them in a variety of strengths. The beers with higher gravities were called "stout porters", so the history and development of stout and porter are intertwined, and the term stout has since become firmly associated with dark beer, rather than just strong beer.
Oatmeal stout is a stout with a proportion of oats, normally a maximum of 30%, added during the brewing process. Even though a larger proportion of oats in beer can lead to a bitter or astringent taste, during the medieval period in Europe, oats were a common ingredient in ale, and proportions up to 35% were standard. Despite some areas of Europe, such as Norway, still clinging to the use of oats in brewing until the early part of the 20th century, the practice had largely died out by the 16th century, so much so that in 1513 Tudor sailors refused to drink oat beer offered to them because of the bitter flavour.
There was a revival of interest in using oats during the end of the 19th century, when (supposedly) restorative, nourishing and invalid beers, such as the later milk stout, were popular, because of the association of porridge with health. Maclay of Alloa produced an Original Oatmalt Stout in 1895 which used 70% "oatmalt", and a 63/- Oatmeal Stout in 1909, which used 30% "flaked (porridge) oats".
In the 20th century many oatmeal stouts contained only a minimal amount of oats. For example, in 1936 Barclay Perkins Oatmeal Stout used only 0.5% oats. As the oatmeal stout was parti-gyled with their porter and standard stout, these two also contained the same proportion of oats. (Parti-gyle brewing involves drawing off the first part of the mash and using it to make strong ale, then remashing the grain and drawing off the second runnings for a less strong variant.) The name seems to have been a marketing device more than anything else. In the 1920s and 1930s Whitbread's London Stout and Oatmeal Stout were identical, just packaged differently. The amount of oats Whitbread used was minimal, again around 0.5%. With such a small quantity of oats used, it could have had little impact on the flavour or texture of these beers.
Many breweries were still brewing oatmeal stouts in the 1950s, for example Brickwoods in Portsmouth, Matthew Brown in Blackburn and Ushers in Trowbridge. When Michael Jackson mentioned the defunct Eldrige Pope "Oat Malt Stout" in his 1977 book The World Guide to Beer, oatmeal stout was no longer being made anywhere, but Charles Finkel, founder of Merchant du Vin, was curious enough to commission Samuel Smith to produce a version. Samuel Smith's Oatmeal Stout then became the template for other breweries' versions.
Oatmeal stouts do not usually taste specifically of oats. The smoothness of oatmeal stouts comes from the high content of proteins, lipids (includes fats and waxes), and gums imparted by the use of oats. The gums increase the viscosity and body adding to the sense of smoothness
History: An English seasonal variant of sweet stout that is usually less sweet than the original, and relies on oatmeal for body and complexity rather than lactose for body and sweetness.
Aroma: Mild roasted grain aromas, often with a coffee-like character. A light sweetness can imply a coffee-and-cream impression. Fruitiness should be low to medium. Diacetyl medium-low to none. Hop aroma low to none (UK varieties most common). A light oatmeal aroma is optional.
Appearance: Medium brown to black in color. Thick, creamy, persistent tan- to brown-colored head. Can be opaque (if not, it should be clear).
Flavor: Medium sweet to medium dry palate, with the complexity of oats and dark roasted grains present. Oats can add a nutty, grainy or earthy flavor. Dark grains can combine with malt sweetness to give the impression of milk chocolate or coffee with cream. Medium hop bitterness with the balance toward malt. Diacetyl medium-low to none. Hop flavor medium-low to none.
Mouth-feel: Medium-full to full body, smooth, silky, sometimes an almost oily slickness from the oatmeal. Creamy. Medium to medium-high carbonation.
Overall Impression: A very dark, full-bodied, roasty, malty ale with a complementary oatmeal flavor.
Comments: Generally between sweet and dry stouts in sweetness. Variations exist, from fairly sweet to quite dry. The level of bitterness also varies, as does the oatmeal impression. Light use of oatmeal may give a certain silkiness of body and richness of flavor, while heavy use of oatmeal can be fairly intense in flavor with an almost oily mouth-feel. When judging, allow for differences in interpretation.
Ingredients: Pale, caramel and dark roasted malts and grains. Oatmeal (5-10%+) used to enhance fullness of body and complexity of flavor. Hops primarily for bittering. Ale yeast. Water source should have some carbonate hardness.
Commercial Examples: Samuel Smith Oatmeal Stout, Young's Oatmeal Stout, McAuslan Oatmeal Stout, Maclay’s Oat Malt Stout, Broughton Kinmount Willie Oatmeal Stout, Anderson Valley Barney Flats Oatmeal Stout, Tröegs Oatmeal Stout, New Holland The Poet, Goose Island Oatmeal Stout, Wolaver’s Oatmeal Stout
Source: 2008 BJCP Style Guidelines, http://en.wikipedia.org/wiki/Stout