A comparative study of oat (Avena sativa) cultivars as brewing adjuncts

Abstract

Brewing with high levels of unmalted oats (Avena sativa) has proven to be successful despite their high contents of β-glucan, protein, and fat. However, little is known about the effect of different oat cultivars on the quality and processability of mashes and worts. Therefore, the aim of this study was to compare the mashing performance of eight oat cultivars, selected because of their low contents of β-glucan, protein, fat, and/or high starch content, when substituting 20 or 40 % barley malt. For this purpose, seven husked (A. sativa L. ‘Lutz’, ‘Buggy’, ‘Galaxy’, ‘Scorpion’, ‘Typhon’, ‘Ivory’, ‘Curly’) and one naked oat cultivar (A. sativa var. nuda ‘NORD 07/711’) were fully characterized using standard methods, Lab-on-a-Chip capillary electrophoresis, and scanning electron microscopy. The rheological behavior of mashes containing up to 40 % of each oat cultivar was measured during mashing by applying a Physica MCR rheometer. In addition, the quality of worts obtained from laboratory-scale mashing trials was analyzed particularly with regard to their cytolytic, proteolytic, and amylolytic properties. The substitution of up to 40 % barley malt with husked or naked oats resulted in significantly higher pH values, β-glucan contents, and viscosities as well as significantly lower soluble nitrogen and polyphenol contents, color values, filtration rates, and apparent attenuation limits. Naked oats contained significantly less β-glucan as well as more protein and starch than the seven husked oat cultivars. The replacement of barley malt with naked oats resulted in a constant extract yield, whereas the use of husked oats caused significant extract losses.