The utilization of hemicellulases in bleaching of kraft (sulphate) pulp is considered as one of the most important new large‐scale industrial applications of enzymes. This is partly due to the great potential of an environmentally safe method. This method has in a short period also proven to be economically realistic. The main enzymes needed in the enzyme‐aided bleaching have been shown to belong to the group of endo‐/gb‐xylanases. Xylanases act mainly on the relocated, reprecipitated xylan on the surface of the pulp fibres. Enzymatic hydrolysis of this specific type of xylan renders the structure of the fibres more permeable. The hydrolysis of xylan or mannan in the inner fibre layers may also enhance the bleachability. In practical process conditions, properties of the enzymes such as substrate specificity and the pH and temperature optima are of utmost importance. The benefits obtained by enzymes are dependent on the chemical bleaching sequence used as well as on the residual lignin content of pulp. The main goals in the enzyme‐aided bleaching of kraft pulps have been the reduction of consumption of chlorine chemicals in the bleaching process and consequently lowering the AOX of the effluents. Enzymes have been applied as a pretreatment both in conventional (C/D)EDED and in ECF (elementary chlorine‐free) bleaching sequences. In the production of TCF (totally chlorine‐free) pulps, enzymes have also been successfully used for increasing the brightness of pulp.

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The optimal pitching rate in high gravity worts (12-16°P) was about 0.3 g/l wet weight (2.3 x 106 counted cells/ml) and per one percent of original wort gravity. In very high gravity worts (20-23°P) the corresponding figure was 0.4 g/l (2.9 x 10* cells/ml). Higher amounts of yeast did not improve the fermentation rate.With increased original wort gravity, flocculation of the yeast weakened and the amount of cropped yeast decreased. The viability of the crop yeast was good.In the conditions used, excessive production of acetate esters occurred only with pitching rates lower than the recommended rate. As the original wort gravity increased, more fermentable extract was metabolized to ethanol rather than utilized for yeast growth. The highest ethanol yield obtained was 10.9% (v/v).

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