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THOUGHT PIECE the carling team

How To Make Beer – Beer Processing After Fermentation

Beer in fermenter ready for further processing. The skimming parachute has been raised after cropping the yeast.

Last month we left the beer making process with a fermenting vessel full of ‘green beer’. What happens next depends on how the beer is to be sold in the market place. A relatively small but noisy sector of the UK market involves cask conditioned ale. Known by some as ‘real ale’ I guess to distinguish it from the unreal ale which emanates from some of the nation’s larger breweries. All ale is real but I suppose some is more real than others! The term is supposed to mean not processed; it is non filtered and unpasteurised. The term ‘craft’ also creeps in but the UK’s largest cask beer brand (Sharps) is made by Britain’s second largest brewer (Molson Coors). I shall leave discussing what craft means for a future blog.

Isinglass – sun dried swim bladders of sub tropical fishes.

For cask, the yeast count needs to be around one million cells per mL, more and you may get yeasty flavours and less it will take much longer to increase the amount of carbon dioxide in barrel as it is put on dispense in the pub. The yeast count is controlled by settling in fermenter; a lot of regional brewers say their beer is blessed by the Sabbath as it stays in FV for seven days but more prosaically it gives the yeast longer to settle out. Otherwise you can use a centrifuge! You need to bypass some beer as yeast which has been through a centrifuge could be a bit giddy and reluctant to go to work again in the cask. Residual protein can also be removed by a dose of auxiliary finings, usually an acidified silicate preparation which will combine electrostatically and remove it from suspension.

You have to give the residual yeast something to ferment so ‘priming’ sugar is added, this time primarily to produce CO2 rather than alcohol. The final ingredient will be isinglass finings; this is an acidified extract of the swim bladders of certain sub-tropical fish. Isinglass has been used for clarifying wine and beer for over three hundred years and has not poisoned anybody yet but its use will stop the product getting a vegan badge. As it is not a proven allergen its use does not need to be declared on the label. The finings has an aggregate positive electrostatic charge and acts with the negatively charged yeast cell and drops into the belly of the cask once its work is done. In a future blog I shall explain a bit more about how to handle cask beer in the cellar and give it the loving care it deserves.

Cask racking from small to large scale. The middle picture shows a typical racking cock with filling tube.

The other 92% of the nation’s beer is called ‘brewery conditioned’ and is prepared for small pack (bottle and can) or keg in the brewery so that it is ready to consume without any further cellar work. All you have to do is couple the keg up, remove the bottle cap or pull the can ring pull. This next process is known variously as conditioning, maturation or aging.

Top is a green beer centrifuge and below the condense on the pipe shows everything must be kept cold.

Our green beer in fermenter will probably be around 4oC. This is the temperature at which water has its maximum density so it is easiest to leave beer at that point which avoids needing more sophisticated vessel jacket control to prevent freezing and only the foolhardy would dare try to rouse a deep conical in an attempt to equilibrate temperatures. The fountain of froth would be spectacular.

Some brewers employ dual purpose vessels, unitanks or FVCTs. Here the beer conditions in the same tank used for fermentation. It has the advantage of saving the wetting losses associated with a transfer from fermenter to conditioning tank but all your tanks need more cooling jackets (covering the entire side and cone of the vessel with sophisticated control to prevent icing during cooling) rather than just the CTs. Your choice!

Smaller brewers have smaller tanks, some are jacketed like the larger conicals and others are not insulated and are contained in cold rooms.

Top: Small dished bottom vertical tanks. In the middle are stacked horizontal vessels and a large conical conditioning tank at the bottom.

Usually the beer will be chilled and centrifuged to remove all residual yeast as it has completed its work in the fermenter. Beer is in-line chilled to as low a temperature as possible without risking freezing. Minus 2oC is easily possible in high gravity beers, this temperature accelerates the formation of haze in beer as proteins and polyphenols complex together. If you then filter the beer cold, the coagulant will be removed so the beer can be chilled in the marketplace or your fridge without throwing a haze. You will sometimes hear the term ‘chill proofing’. Once the low temperature is reached, chemical reactions cease and there is little point in holding the beer any longer and it simply becomes stock to be held to keep the packaging schedule going.

You will be aware of some European brands which make a virtue of long storage. Budvar Reserve is kept in cellar for 200 days, they admit that such a lengthy sojourn in tanks below Ceske Budejovice is expensive and will charge you £2.45 for a 330mL bottle. Science says it is not necessary to keep beer that long and indeed yeast autolysis can occur which can give unpleasant flavours. The Czechs would do well to hold the beer in fermenter for longer, chill to a lower temperature and add CO2 at a carbonator rather than relying on the slow natural build-up of gas. Decoction mashing is not necessary either and possibly deleterious to flavour. Just saying!

The Czechs are not alone, German brewers will often add ‘krausen’ which is actively fermenting wort to the beer as it leaves fermenter in an attempt to kickstart the secondary fermentation to remove the butterscotch, acetaldehyde and sulphidic flavours left behind by putting the FV cooling on as soon as the target specific gravity is reached. Curiously I know brewers who swear that carbonation produced by secondary fermentation gives a ‘better’ foam than that generated by injecting the gas at a carbonator; I cannot understand how a carbon dioxide molecule can remember where it came from in order to behave differently – unless there is something else going on. Any scientists out there?

 

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