Yorkshire Square

The Yorkshire Square fermenting system was perfected well over 200 years ago. Though it has fallen out of favor in modern times due to the amount of time and maintenance it requires, it produces a distinctively flavored beer that is impossible to replicate with other factory methods. For this reason it is now mostly practiced by the smaller, independent breweries which focus on quality, such as Samuel Smith's and Black Sheep.

A Yorkshire Square vessel is a two-story system consisting of a shallow chamber approximately two meters high, above which is a walled deck. Cooled wort, the liquid extracted from malted barley, is fermented by a special yeast in the lower chamber, while the yeasty head settles on the deck above.

During the first stage of fermentation, the fermenting wort is periodically pumped from the bottom of the chamber over the yeasty head, to keep the yeast mixed in with the wort. Later, the mixing is stopped and the wort in the chamber allowed to settle and cool gently.

Most of the yeast rises onto the deck, and is left behind when the beer is drained from the chamber.

The whole process takes at least six days. However, beer straight from a Yorkshire Square vessel will still have a harsh flavor. Before it can be considered drinkable, the residual yeast must be allowed to ferment any remaining sugar, producing a little extra alcohol and carbon dioxide, which mellows the beer and produces a wonderful balance of taste and aroma. This conditioning begins in tanks at the brewery and continues after the beer is filled into casks, hence the phrase 'Cask Conditioned'.

It has been suggested that the Yorkshire square system was developed with the help of Joseph Priestley who, in 1722, delivered a paper to the Royal Society on the absorption of gases in liquids. In addition to being a scientist, and later a political dissident, he was for a time the minister of a Unitarian church in Leeds. During that period he lived next to a brewery on a site that is now the Tetley's brewery.

Historically, the Yorkshire Square vessel was constructed from Yorkshire Sandstone, but Welsh slate quickly proved to be the material of choice. A modern innovation is the so-called 'Round Square' pioneered by the Black Sheep brewery, which is built from stainless steel. The round shape makes it easier to clean out (a task that requires personnel to physically climb in to the vessels) between brewing cycles.