Yorkshire Square is a unique fermenting vessel that originated in the north of England. The vessels were originally made of stone, followed by slate, and modern vessels are made of stainless steel. They are cubic in shape and were originally quite small (50 hl) but modern squares can be 250–300 hl in size. The vessel is specially designed to assist in yeast collection. The vessels have a lower compartment that is separated from an upper deck with a 1-meter wide hole in the center. A highly flocculant, top-fermenting yeast is used to ferment the ale style and the fermenting wort is occasionally roused (circulated by pump) from the lower to upper deck to keep the fermentation going and yeast in suspension. See flocculation. During fermentation, yeast foam wells up through the hole onto the upper deck where it remains; beer retained in the yeast separates from the foam and runs back into a pipe that runs from the upper deck through to the bottom of the vessel below. Because of its appearance, this pipe is referred to as the “organ pipe.” At the end of fermentation the rousing is stopped and fresh yeast is skimmed from the upper deck. The Samuel Smith’s Brewery of Tadcaster still uses the Yorkshire square system and the Black Sheep Brewery in Masham adopted this classic fermentation system when they started up in 1991. Tetley’s Cask Bitter was a well-known ale fermented in these vessels. The system is now rare, but beers fermented in Yorkshire squares are said to be full bodied and often fruity in character.