See study by W. S. Baring-Gould (1969) and D. R. Anderson (1984).
Stout and porter are dark beers made using roasted malts or roast barley. There are a number of variations including Baltic porter, dry stout, and Imperial stout. The name Porter was first used in 1721 to describe a dark beer popular with street and river porters of London that had been made with roasted malts. This same beer later also became known as stout, though the word stout had been used as early as 1677. The history and development of stout and porter are intertwined.
Stouts have a number of variations.
In modern brewing a stout is differentiated from a porter by the addition of roasted barley. In today's style guidelines there is a difference between stout and porter and it is not related to alcohol strength.
Milk stout was not very widely distributed before Mackeson's Brewery acquired the patents to produce it in 1910. Since then its production has been licensed to other brewers.
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. However, 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 sixteenth century, so that Tudor sailors refused to drink oat beer offered to them in 1513, because of the bitter flavour.
There was a revival of interest in using oats during the end of the nineteenth century, when 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 75% "Oatmalt", and a 63/- Oatmeal Stout in 1909 which used 30% "Flaked (Porridge) Oats".
But by the early 20th century these beers had all but disappeared. 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.
One of the first to follow Samuel Smith was the Broughton brewery in the Scottish Borders with their Scottish Oatmeal Stout, a 4.2% beer they have made since 1979 with roasted barley and pinhead oats. Young's Brewery of London were not long after with their 5.2% Oatmeal Stout, a beer that is mainly made for the North American market. One of the most notable of the USA versions is the Anderson Valley Brewing Company's Barney Flats Oatmeal Stout, a bottle conditioned stout of 5.7% strength that has won several awards. In Canada, McAuslan Brewing's St. Ambroise Oatmeal Stout has also attracted attention and a significant award.
Oatmeal stouts are now made in several countries, including Australia with Redoak of Sydney producing a 5% Oatmeal Stout and WinterCoat of Denmark brewing a 5.9% Oatmeal Stout using roasted barley and chocolate malt.
Oatmeal stouts usually do not specifically taste 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.
The ABV of these coffee flavoured stouts will vary from under 4% to over 8%. Most examples will be dry and bitter, though others add milk sugar to create a sweet stout which may then be given a name such as "Coffee & Cream Stout" or just "Coffee Cream Stout". Other flavours such as mint or chocolate may also be added in various combinations.
The first known use of oysters as part of the brewing process of stout was in 1929 in New Zealand, followed by the Hammerton Brewery in London, UK, in 1938. Several British brewers used oysters in stouts during the "nourishing stout" and "milk stout" period just after the second world war.
Modern oyster stouts may be made with a handful of oysters in the barrel or, as with Marston's Oyster Stout, just use the name with the implication that the beer would be suitable for drinking with oysters.