2001

Virkajärvi, Ilkka

Fermentation is the most time consuming step in the production of beer and therefore the effective use of fermentation vessels is a crucial element in brewing economy. One means of increasing the productivity of a batch process is to convert it to a continuous one. Experiments in continuous fermentation emerged during the 1950s and 1960s, but by the end of 1970s most of them had been closed down. Immobilization technique revitalised continuous fermentation research in the 1980s and led to industrial applications in the secondary fermentation and in the production of low-alcohol beers. This work demonstrated that an immobilized, continuous main fermentation is a feasible process for production of lager beer. The immobilized main fermentation was stable for more than 14 months both in fermentation efficiency and in aroma compound formation. The formation of aroma compounds could be controlled by varying the composition and amount of gas feed into the first fermentation stage. The division of immobilized main fermentation into an aerobic and an anaerobic stage appeared to solve problems related to yeast growth and viability. The carrier material affected the formation of flavour compounds in small-scale fermentations. Moreover the effect varied with the yeast strain used. The carrier affected the economy of immobilized fermentation: the carrier cost could be as high as one third of the investment. When a cheap carrier is used the investment cost for a continuous, immobilized process was estimated to be only about 70% of the investment cost of a batch process.