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Cask Racking
After a period of around seven days in total in the fermenting vessel (FV) the beer is ready to Rack.
The temperature will be between 10 and 12°C, a thin head of yeast will remain on top of the beer in the FV and a certain amount of yeast will have settled to the bottom. The FV’s have a plug placed in the outlet before filling which acts as a weir holding back the yeast which has settled, preventing it from running into the cask racker.
The cask racker or racking machine has been designed to allow a continuous flow of beer through the machine, even when switching from one cask to another This is to ensure that there is no shock caused by shutting a valve off and on, possibly dislodging a slug of yeast from the FV. This design involves a double barrel set up whereby two 4” tubes are connected one above the other by two 1” tubes. The beer is allowed to run into the lower tube directly from the FV and from that tube through a flexible hose to the cask filling valve. When the cask filling valve is shut to allow transfer to another cask the beer continues to run into the lower 4” tube but is the diverted up into the upper 4” tube via the interconnecting 1” tubes. When the filling valve is opened again the beer runs back down from the upper 4” tube thus creating a sort of bellows effect which ensures a steady flow of beer from the FV.
Cleaning and sterilising is very important since any contamination in the racker will be carried into all casks filled. A regime of hot acid detergent and rinsing with scalding water is used.
The casks themselves are washed on an semiautomatic washer which put the decanted casks through a cycle of
Cold rinse, hot detergent wash followed by steam sterilisation.
Once the casks have cooled the keystones are hammered in and auxiliary finings are added to the cask before filling.
Once filled the casks are sealed with a plastic shive in the bung hole.
The casks are then stored in a cellar where the temperature is maintained at around 12 to 15°C. During this time which is a minimum of five days the small amount of yeast left in suspension produces a secondary fermentation building up a pressure of CO2 which dissolves in the beer to produce the natural sparkle.
This secondary fermentation is important since when the cask eventually reaches the pub cellar it will be vented to allow excess CO2 to escape. This escaping CO2 has a cleansing effect on the beer removing certain volatile flavours and aromas associated with freshly racked beer.
Prior to being sent to the pub, casks are opened and a quantity of isinglass finings are added which in conjunction with the auxiliary finings already added will cause the yeast and protein carried in suspension in the beer to form large clumps, or flocks, which settle to the bottom of the cask over a period of some 24 hours.
Isinglass finings are prepared from the swim bladders of certain tropical species of fish. The protein which comprises these swim bladders is dissolved in tartaric and phosphoric acid which hydrolyses the protein creating a solution which, when dissolved in beer, has an negative electrical charge. Since the cell walls of yeast have an electrically positive charge the two mediums attract one another creating the large flocks which settle to the bottom of the cask leaving the beer clear and sparkling.
{Image of isinglass fining and image of swim bladder}
Cask conditioned beer should always be presented bright and clear. A cloudy pint simply highlights the careless attitude of the brewer or publican, or both.
