One of my favorite stouts is Oesterstout by the Schelde Brewery.
The website states:
During the brewing process, the wort of the beer is pumped across the oyster shells.
Is this what gives it it's distinct taste? In Denmark, another more easily available Oyster stout is Marston's Oyster Stout. Do all Oyster Stouts follow this particular process, or is it more of a sales pitch?
Oyster stout traditionally uses oysters as part of the brewing process, and that is the flavour that differentiates them from other stouts. While it is traditional to use oysters, some modern breweries use artifical flavours in their oyster stouts, or simply say that they are intended to be eaten with seafood.
You mention Marston's Oyster Stout, which is one example of an oyster stout that doesn't use actual oysters in the brew. From their website:
Marston’s Oyster Stout is a dark, creamy, smooth, clean tasting English stout. It doesn’t contain oysters, just called Oyster Stout as this style of ale is a great complement to shell fish dishes.
Just had a bottle of Marston's Oyster Stout two days ago (10/25/14), the label states it is brewed with oyster shells.
Oyster stouts are indeed brewed with oysters. The occasional offering that we sell (Niagara College Teaching Brewery), uses oysters at the end of the mash regime (hot soaking of the grains). The idea here is that you are extracting calcium carbonate from the shells, which helps reduce the tannic astringency that can result from the roasted grains used in stouts. This is the same reason/benefit that stouts are traditionally brewed in areas with relatively hard water. It also happens to be the perfect temperature for cooking oysters.
Oysters cooked or uncooked could be added at other parts of the process, but may not have the same impact on reducing astringency. There is a subtle undertone of the oyster that makes it into the finished product, but your palate may vary and may or may not detect it (depending on process and quantity used).
Oysters used to be served as an accompaniment to beer in pubs in Victorian England, so the first beers called Oyster Stouts were probably beers intended to compliment oysters rather than containing them. Later someone discovered that you could use crushed Oyster shells as a fining agent in beer and later still someone actually added the oyster meat, probably as a marketing gimmick since oysters aren't going to add much to the flavour.
So it's fine for oyster stout to not contain oysters.
This, "The idea here is that you are extracting calcium carbonate from the shells, which helps reduce the tannic astringency that can result from the roasted grains used in stouts." from John, was most helpful and logical. Understanding how chemistry functions in brewing becomes logical once you ponder the explanation. Thanks, John.
If it is an Oyster stout then it probably should have contact with ACTUAL oysters. Using the shells is a cop out that is like stone soup.
Checkout new brewery Hammertown in London who do it properly: "In 1938 the original Hammerton Brewery was famous for being the first in the world to use Oysters as part of the brewing process. In this new recipe we’ve used a variety of flavoursome malts, including a good dose of oats. Fresh wild Maldon oysters are then added to the boil to add a subtle extra complexity to the taste of this stout."
