Optimization of the Fermentation Process and Sensory Evaluation of Wild Loquat (Uapaca kirkiana) Fruit Wine

Uapaca kirkiana (family Euphorbiaceae), known as wild loquat, is a tropical indigenous fruit tree. The fleshy pulp of the U. kirkiana fruit is eaten fresh or processed into a variety of products, including juices, squashes, wines, sweet beer, porridge, jams and cakes. However, the commercialisation of the fruit wines still remains a challenge due to a lack of consistency in product quality. The purpose of this study was to use response surface methodology (RSM) to optimise the fermentation of wild loquat (U. kirkiana) fruit wine. A study to investigate the relative contributions of two predictor factors (Brix value and yeast quantity) to the quality of wine was conducted using RSM. Design Expert 7 was used for a central composite design (CCD). Thirteen (13) runs of wine were produced as outlined in the CCD for the independent variables. The responses measured included alcohol by volume (ABV percentage), density, real extract (Er), original extract, Plato, real degree of fermentation (RDF), pH, calories and colour. Overall, Brix had the greatest influence on responses, showing substantial correlations whether they were positive or negative. In contrast, yeast and responses tended to have weaker correlations, with the exception of pH, where the converse was true for both independent components. The optimum values of Brix and yeast for the fermentation of U. kirkiana wine were found to be 24.44°Bx and 1 g, respectively. The predicted values for the responses are 11.83% (ABV), 1.00539 g/cm³ (density), 75% (RDF), 5.53 EBC (European Brewery Convention) colour, 350.998 kJ/100 mL or 87 kcal and pH of 3.5. The developed models could predict the quality of wine developed from wild loquat fruit. It was observed that wine samples with high Brix and moderate yeast quantities had more intense flavour characteristics. In contrast, wine samples with extreme (high and low) initial yeast levels exhibited strong off odours and sourness.