1993

Home, Silja

β-Glucans are the main components of barley cell walls. The cellular structure of barley endosperm must be enzymatically degraded during the germination process before the starch can be released and hydrolyzed in mashing. In the present study a selection procedure emphasizing the structural properties of the barley grain and the degradation of β-glucans during malting was developed. The milling energy of barley or acid extract viscosity were useful analytical methods for the selection of barley lines in preliminary screening. A small scale micromalting with subsequent determination of milling energy of malt predicted the modification rate and was recommended for the selection phase. In the final evaluation the major emphasis must be placed on the homogenity of cell wall degradation. The quality of barley is affected by the weather conditions during the growing season. The addition of fungal cellulase together with gibberellic acid in malting, a method called 'enzymatic abrasion', was used to adjust the quality of malt. This resulted in accelerated malt modification, improved β-glucan degradation and marked improvement in beer filtration. Mash separation or beer filtration problems are occasionally encountered in the brewing process. These may be caused by the uneven quality of malt or by the use of unmalted barley as an adjunct. Mashing-in at 48°C was most optimal for the activity of endogenous β-glucanase in malt. By extending the time at the mashing-in temperature it was possible to promote β-glucan degradation. Attention must also be paid to the mash tun design. Efficient stirring and heating led to increased release of β-glucans. Two other mashing variables, mash thickness and grist coarseness, also affected the β-glucan content in wort. The addition of a fungal cellulase preparation either in mashing or in fermentation provided an efficient means of improving beer filterability. The advantage of using the external enzyme in mashing is that it is inactivated during boiling. The increased cost of the manyfold amount of enzyme needed compared with the addition in fermentation can probably be covered by increased brewhouse yield and improved lautering. A novel solution to beer filtration problems is the use of glucanolytic brewer's yeast. However, general acceptance of the use of genetically modified yeasts still requires some time.