This picture gives a better view of the fob trough and the feeder tank. You will note that the contents of the feeder trough has a small amount of yeast or "Krausen" on the surface. This serves to keep the wort that has drained from the fob to remain sterile by producing not only a cover but also a co2 layer. It also introduces healthy new yeast (by reproduction) to pick up where the primary yeast may have become dormant.
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To give some idea of scale to the casks the picture below shows the head brewer at Marstons standing beside one of the 7hL (700 litre)litre casks.
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Looking at the front end of the cask you will see the cross shaped trunnion (one of which is on the rear too) that fits into a mount to suspend the cask. The two lines of tubing run to the cask attemperator that is used to keep the temperature down to as close as possible to 19 degrees celcius. Just below the top is the feeder arm that allows the wort from the collapsed fob to return to the cask from the feeder trough.
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Out of sight is the swans neck that directs the fob in the trough above from the top of the cask, and also the drain tap at the bottom of the cask.
You will see from the picture below that the is also a small tap to the right side. There is only cask in each set that has this which is used to take samples from to plot the attenuation of the brew.
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