Influence of corn size distribution on the diastatic power of malted barley and its impact on other malt quality parameters.

Detailed studies were carried out on the influence of corn size distribution on the values obtained for diastatic power (DP) of commercially malted barley. Malted barley was screened using a screening box, and the DP activities of the different corns retained on the different compartments of the screening box were determined. The malt samples retained on the 2.8 mm screen had the highest DP activity, whereas the small corns (<or=2.2 mm) had the lowest levels of DP activity. When the DP results of the corns retained on the different screens were weighed in relation to the percentages of grains retained on each screen, the results obtained were very similar to those obtained from the mixed, unscreened malt samples. The results indicate that the higher the percentage of large corns in a malt sample, the higher the levels of DP found in the malts. In malt samples from both the Decanter and Maresi varieties/cultivars, regression analysis showed that large corns accounted for 87% of the variation in DP. These studies confirmed that corn size distribution is a very important factor in determining the DP level of malted barley. The study is of commercial significance because within a variety, with a similar range of nitrogen, large corns produce malt of higher DP. When the percentage of large corns is high, this should give extract with improved fermentability (yield of fermentable sugars). The gelatinization properties of different grain size fractions, some of which were malted individually, were also studied using a rapid visco analyzer (RVA), and this showed that kernel size had an important impact on the physical properties and malting performance.