Continuous secondary fermentation and maturation of beer in an immobilized yeast reactor.

Pajunen, E., Gronqvist, A. and Lommi, H.

Abstract
The long maturation process required by lagers is often the most time consuming stage in the production of beer of this type, and it would obviously be a great advantage to the brewer if this time could be shortened without impairing the quality of the beer. This paper describes a process and equipment devised for that purpose, which at the time of writing had been operated successfully on a commercial scale at the Sinebrychoff Brewery in Helsinki, Finland, over a period of several months. After completing primary fermentation, the beer is centrifuged to remove the yeast, then subjected to a heat treatment to convert certain chemical precursors of diacetyl either to diacetyl or to other compounds (in fact it turned out that some of the free diacetyl already present is also converted into something else) and then passed to a packed bed immobilised yeast reactor, in which yeast of the brewery's normal strain is immobilised on "Spezyme GDC", a commercial granular cellulose carrier material. Final attenuation and the reduction of the diacetyl content to a level below the off flavour threshold can be achieved in as little as two to three hours, resulting in a finished beer said to be indistinguishable from that which has been conventionally lagered for the usual two to three weeks. The advantages in saved time, saved space and greatly increased flexibility (allowing production rates to be altered at short notice in times of fluctuating demand) are considerable.
Keywords : brewers' yeast brewing centrifugation continuous process diacetyl equipment flavour heat immobilised lager maturation quality secondary fermentation time