Effect of two-stage fermentation temperatures and particle size on stability and sensory characteristics of Umqombothi

Abstract

The consumption of Umqombothi, a traditional indigenous pale buff, pinkish-brown to cream-colour after sieving with a yoghurt-like flavour alcoholic beverage produced from sorghum malt and maize malt is widespread in several regions of South Africa. The aim of the research was to determine two stage fermentation and particle size on stability and sensory characteristics of Umqombothi using three different fermentation temperatures namely, U1 (30-30oC), U2 (30-25oC), and U3 (25-30oC), and determine the effect of 24 hours fermentation on the product. Sensory evaluation was conducted on the final products. Three different particle sizes of sorghum malt and maize malt of Umqombothi beer were compared: normal, coarse, and fine powder of sorghum malt and maize malt. Fermented Umqombothi samples were collected before and after the first fermentation, after cooking, at the end of the second fermentation, from the final product, and after fermentation for 24 hours. The microbial content [lactic acid bacteria (LAB), total viable count (TVCs), yeast and moulds (Yeasts), and coliforms] of samples were determined, as well as certain chemical and physical factors [pH, total soluble solids, specific gravity, ethanol, and colour]. The respective final products were subjected to a consumer sensory evaluation based on taste, aroma, appearance, colour, and overall acceptability. Lactic acid bacteria were the most predominant microorganisms throughout the Umqombothi manufacturing process. Sample U1 (30-30oC) had a substantially higher (p < 8.24) LAB count than U2 and U3, which might be attributed to LAB's optimal temperature range, U1 also exhibited significantly (p < 3.45) lowest pH, higher lightness and higher TSS as compared to the U2 and U3. All three fermentation temperatures contained the same percentage of alcohol (2%ABV). Umqombothi brewed at U1 (30-30oC) was also preferred by the consumers. To produce Umqombothi with uniform organoleptic characteristics, it is therefore recommended to perform first and second fermentation at (30-30oC). At this temperature condition, the coarse particle size (sorghum malt and maize malt) produced a significantly (p < 1.44) highest alcohol content and lowest pH levels (3.46). The significantly (p < 4.02) highest overall acceptability was obtained with the normal particle size. Between coarse and normal particle sizes (sorghum and maize malt), there was no significant difference in taste, texture, or colour. The Umqombothi ingredient's fine powder particle size was considerably (p < 0.05) smaller than both the sorghum and maize malts' particle sizes. This difference in particle size had an impact on the development of yeast and LAB during fermentation. Coarse (sorghum malt and maize malt) particle size Umqombothi was the most preferred during consumer sensory evalution. Because of the significantly (p < 4.08) low pH, and significantly (p < 3.44) high alcohol content, coarse particle size was selected to use in subsequent experiments. Laboratory Umqombothi was therefore produced using coarse particle size and 30oC for both fermentation temperature stages, and a consumer sensory evaluation was performed to compare the final product with traditionally preparedUmqombothi. A smoky flavour was detected by a panelists because Umqombothi prepared in the townships is brewed outside over a wood fire. Laboratory Umqombothi was described as thick and sour with a sweet aftertaste and had the lowest mean overall acceptability of 3.50. With an mean overall acceptability mean of 3.74, Umqombothi collected around Ezimbacwini was described as weak and watery. And Umqombothi collected around Langabuya, had the significantly (p < 0.05) highest mean value for appearance, colour, aroma, taste, and texture. Township Langabuya Umqombothi was the most preferred during consumer sensory evaluation.