Development of a database of sorghum cultivars in southern Africa, with emphasis on end-use quality, particularly brewing quality

Abstract

The level of sorghum production in southern Africa is very low compared to the rest of Africa. Low adoption rate of available improved sorghums due to lack of information about their properties has been identified as a problem. This problem may have contributed to the low level of sorghum production and utilisation. A database on agronomic properties, grain, and processing and end-use quality attributes of sorghum cultivars available in southern Africa was developed in order to improve adoption rate of these improved sorghums. This database information was provided for easy access to both sorghum producers and processors, which will ensure improvement in sorghum production and utilisation. A total of 51available improved sorghum cultivars were included in the database. However, the available information on the enduse quality of the sorghum cultivars is limited, especially with regard to selection of suitable cultivars for specific applications, such as adjunct in lager beer brewing. Identification of suitable sorghum type(s) as for use as adjunct in lager beer brewing remains an aspect yet to be systematically researched, which will enable selection of suitable sorghum type(s).Five different sorghum types were selected for determination of their grain and lager beer wort quality properties. The types were white tan-plant, white non-tan plant, red non-tannin, white tannin (type II) and red tannin (type III). Grain hardness ranged from corneous to floury, with non-tannin types having mostly corneous to intermediate endosperm. The tannin sorghum types had mostly floury endosperm, as expected. The sorghum types with floury endosperm had higher protein content than the corneous endosperm types. Grain tannin content was up to 45.3 g catechin equivalent/100 g, which contributed significantly to the level of total phenols in the grain. Wort samples were produced by mashing the milled sorghum with exogenous enzymes. The wort quality attributes was mostly influenced by the grain tannin property, which correlated significantly and negatively as follows: wort extract (p<0.001, r = -0.846), fermentable sugars (p<0.001, r = -0.810) and FAN (p<0.1, r = -0.498). This poor wort quality can be linked to tannin inactivation of the exogenous enzymes during mashing. Tannin inactivation by steeping in a dilute NaOH solution did not consistently improve wort quality. Contrary to expectations, tannin still remained significantly and negatively correlated with wort quality attributes, but with slightly lower correlation coefficients. Sorghum malting combined with exogenous enzymes mashing yielded great improvement in wort quality. Decortication of tannin sorghums, as well as compositing with white tan-plant types can be considered in the application of tannin sorghum types as adjunct. The red non-tannin sorghums, in terms of wort extract, FAN and fermentable sugars have potential as adjunct in lager beer brewing, due to their similar wort quality attributes to white tan-plant sorghums. Brewing trials with red non-tannin sorghum types is necessary in order to determine their beer brewing and beer quality properties in comparison with white tan-plant sorghums, which are currently used commercially.