Comparative Analysis of Grain Sorghum and Corn as Raw Materials for Bioethanol Production using Very High Gravity Fermentation

Global warming is reducing the availability of conventional feedstocks for bioethanol production, particularly corn. Therefore, grain sorghum is a viable choice because it is naturally drought-resistant and cost-effective. In Ukraine, sorghum can reduce raw material expenses by 15–20% in arid regions. The aim of this study is a comparative assessment of the technological characteristics of mash and wort from grain sorghum and corn prepared using VHG technology.

The grain sorghum hybrid “Brigga” was compared with the corn hybrid “DKS 3730”. Wort with dry matter >270 g/L was prepared via hydroenzymatic treatment. Dynamic viscosity was measured using a rotational viscometer. Fermentation was conducted using dry yeast, followed by distillation and chromatographic analysis to determine ethanol concentration and by-products.

Both grains have similar starch levels (64–78%), but differ in protein and non-starch polysaccharide content. After 72 hours of fermentation, both wort types contained approximately 14% vol. ethanol, with a yield of 1.52–1.54 g/(l·h). Raw sorghum wort distillates showed 11.1% lower levels of volatile by-products than corn.

Studies show that sorghum wort maintains a low viscosity despite higher hemicellulose and β-glucan content. This thinner consistency of sorghum mash is advantageous for VHG fermentation as it allows for higher grain loading while maintaining efficient fermentation.

Grain sorghum demonstrates a technological advantage over corn in bioethanol production using VHG technology. Understanding these approaches will help achieve post-fermentation ethanol concentrations exceeding 18% v/v, improving the economic efficiency of biofuel production.