Optimizing the Malting Conditions of Landrace Six-Row Arupo S Barley Adapted to Grow in Tropical Nigeria

Abstract

The major climatic limitations associated with barley production in the tropics are temperature, humidity, and soils. Arupo S is a six-row landrace barley variety successfully grown in Nigeria, where environmental conditions are often unfavorable. Arupo S is a semi-dwarf, medium maturity with very high yield potential under favorable conditions. It has excellent lodging resistance and good levels of resistance to most diseases, for example, stem rust, leaf rust, and so on. It has good malting quality. Arupo S barley malted at a wide range of temperature conditions (16–25°C) produced malts that met the requirements for brewing purposes. The results of this study showed that the growing conditions of Arupo S barley under irrigation (flooding) did not have any observed negative impact on the quality of malt made from Arupo barley. Arupo S barley steeped and germinated in the temperature range 16–25°C developed good levels of amylolytic enzymes (α-amylase and β-amylase) and produced good hot water extracts (HWE), free amino nitrogen (FAN), amino acids, and reducing sugars. Although the malt made at 25°C developed the least amount of amylolytic enzymes and FAN products, it produced the highest levels of HWE and reducing sugars (glucose and maltose). On the other hand, Arupo S malt made at 18°C developed higher levels of amylolytic enzymes but gave lower amounts of HWE, especially at day 4 of germination. In terms of amino acid distribution in the worts of malted Arupo S barley, the malts made at the lower temperatures of 16 and 18°C gave higher levels of the individual amino acids. The malt made at higher temperatures also produced reasonable amounts of individual amino acids. These results show the difficulties of using only a few parameters in assessing malt quality, indicating that a holistic approach is required when assessing barley and malt quality. Furthermore, this study showed that using a higher malting temperature to produce malt from Arupo S barley in hot countries where malting temperature is difficult to control will not have much detrimental effect on the quality of the malt produced. This is an advantage because use of refrigeration during malting would be expensive.