Comparison of Waxy vs. Nonwaxy Wheats in Fuel Ethanol Fermentation

Fermentation performance of eight waxy, seven nonwaxy soft, and 15 nonwaxy hard wheat cultivars was compared in a laboratory dry-grind procedure. With nitrogen supplements in the mash, the range of ethanol yields was 368-447 L/ton. Nonwaxy soft wheat had an average ethanol yield of 433 L/ton, higher than nonwaxy hard and waxy wheat. Conversion efficiencies were 91.3-96.2%. Despite having higher levels of free sugars in grain, waxy wheat had higher conversion efficiency than nonwaxy wheat. Although there was huge variation in the protein content between nonwaxy hard and soft wheat, no difference in conversion efficiency was observed. Waxy cultivars had extremely low peak viscosity during liquefaction. Novel mashing properties of waxy cultivars were related to unique pasting properties of starch granules. With nitrogen supplementation, waxy wheat had a faster fermentation rate than nonwaxy wheat. Fermentation rates for waxy cultivars without nitrogen supplementation and nonwaxy cultivars with nitrogen supplementation were comparable. Ethanol yield was highly related to both total starch and protein content, but total starch was a better predictor of ethanol yield. There were strong negative relationships between total starch content of grain and both yield and protein content of distillers dried grains with solubles (DDGS).