Scaleup of immobilized yeast bioreactor for continuous fermentation of beer.

Yamauchi, Y., Kashihara, T., Murayama, H., Nagara, A., Okamoto, T. and Mawatari, M.

Abstract
A three stage continuous bioreactor system for use in breweries is described. In the first stage, a suspension of yeast in wort is stirred and aerated, resulting in a lower wort pH, the consumption of amino acids by the yeast and the formation of higher alcohols. Suspended yeast is removed by centrifugation as the wort is transferred to the second stage, a bioreactor containing yeast immobilized on porous glass beads, in which primary fermentation is carried out. In order to accelerate the maturation process, the green beer leaving the second stage undergoes heat treatment to convert acetohydroxy acids (precursors of vicinal diketones) to a mixture of vicinal diketones and acetoin, with the latter predominating, before the remaining vicinal diketones are eliminated by a relatively brief maturation in a bioreactor of the same type as is used for primary fermentation. The development of a large scale continuous fermenting plant to test the industrial applicability of the system, following the successful development and testing of smaller pilot systems since the mid 1980s, is described. It was found that although beer quality was unaffected by the scaling up of the system, the operational stability of the reactors deteriorated to a certain extent. The possible reasons for this and potential solutions to the problems are discussed.
Keywords : beer bioreactor brewers' yeast continuous process fermentation immobilised maturation performance quality