Four fermenting vessels as built in the 1920's to 1930's, three of which have no linings. Because the timbers have been allowed to dry out the hoops have dropped and gaps opened up between the staves. These vessels would need lining with polypropylene or stainless steel to bring them back into use. Fermenting vessel No 20 has a stainless steel lining and is used as a header tank for chilled liquor used in fermentation temperature control.

Highgate have an odd assortment of fermenting vessels with linings of copper, stainless steel and polypropylene. All our vessels are designed to hold around 70 barrels (39 years drinking at the recommended 21 units per week!), but some will ferment smaller amounts depending on the position of the attemporator (the device through which we pass the chilled liquor to control the temperature during the fermentation). At the start of the fermentation enough yeast has to be added to the wort to achieve a yeast count of 8-10 million yeast cells per millilitre of wort. While oxygen is present these yeast cells will divide 2 - 3 times, producing a yeast count of anything up to 80 million per millilitre. When the oxygen is used up the yeast move into a phase of anaerobic growth, the waste products of which are alcohol and carbon dioxide. Highgate use a top fermenting yeast for their ales so at the end of fermentation the yeast cells rise to the top of the vessel where they are removed using a vacuum system. Some of this yeast will be chilled to 4C for storage and further use, the rest will be discarded. Around one inch of yeast is left on top of the beer after skimming in order to prevent oxidation of the product. Fermentations are usually over in around 48 hours, but the beer will remain in the fermenting vessel for at least seven days.

All vessels at Highgate are cleaned by hand after first checking that levels of carbon dioxide are acceptably low. It is interesting to note that if you fell into an actively fermenting vessel you would suffocate before you could drown!