Process Optimisation and Quality evaluation of rice wine

Abstract

Rice wine is globally consumed alcoholic beverage, particularly in Asian countries and several regions of India. Beyond its cultural significance, rice wine serves as a vital medium for value addition in agriculture, effectively transforming surplus grain into a premium product with an extended shelf life. Rice wine production offers high economic returns and is highly remunerative. However, the potential of rice varieties specific to Kerala for use in wine production has not been explored. In the present study, entitled “Process optimisation and quality evaluation of rice wine”, Kerala white rice variety Ptb 47 (Neeraja) was selected to optimise fermentation conditions for rice wine production and quality evaluation of the developed wines. Fermentation was conducted using commercially available baker’s yeast and pure yeast strain (MTCC 2633). The various levels of inoculum concentration (1 - 5%), sugar content (0 - 40%) and water content (30 -70%) were optimised using Response Surface Methodology (RSM) with twenty runs across 7th, 14th, 21th, 28th and 35th days of fermentation. The effects of these variables on responses such as total score of organoleptic evaluation and physicochemical properties, including alcohol content, pH, total soluble solids, total sugar, clarity and wine yield were analyzed. A comparative analysis of these optimized conditions and their effects on total scores of organoleptic evaluation and physicochemical qualities across different fermentation days was conducted and found that the most suitable fermentation duration is 21 days for rice wine prepared using baker's yeast as well as for rice wine prepared with a pure strain. The optimal points for process optimisation of rice wine prepared using baker’s yeast were inoculum concentration of 3.43 %, sugar content of 40 % and water content of 67.27%. The responses were observed as total score of 17.2, alcohol content of 14.2 %, pH of 3.03, TSS of 12.84°B, clarity of 0.48A, total sugar of 5.75 % and wine yield of 48.75 %. Similarly, rice wine prepared using pure strain were obtained optimal values as inoculum concentration of 3.38%, sugar content of 38.92 % and water content of 63.16 %. The responses were observed as total score of 17.15, alcohol content of 12.5 %, pH of 3.12, TSS of 15.26°B, clarity of 0.48A, total sugar of7.12 % and wine yield of 48.58 %. Hence these two treatments were selected for further studies. The nutritional qualities like, total sugar content of the rice wine prepared with the pure strain was 7.12%, which was slightly higher than the 5.75% observed in the rice wine produced with baker’s yeast. Similarly, the reducing sugar content was 5.1% in the pure strain fermentation, compared to 3.6% in the baker’s yeast treatment. The protein content was determined to be 1.63% in rice wine prepared using the pure yeast strain, which was comparatively higher than the 1.40% observed in rice wine fermented with baker’s yeast. The energy value was found to be 107.07 Kcal/100 ml in the baker’s yeast treatment, exceeding the 104.02 Kcal/100 ml recorded for rice wine prepared with pure strain. The mineral composition of the rice wines was also assessed and the results highlight that rice wine produced with baker’s yeast generally exhibited slightly higher concentrations of minerals and similar trend were also observed in vitro mineral availability. It may due to the comparatively higher acidity and alcohol content in wine through improved solubilisation. Moderate scavenging activities were observed for the selected rice wines which is less than that of other white wines. GC–MS analysis of rice wine revealed presence of alcohols, esters and hydrocarbons, as key volatile compounds shaping its aromatic and chemical profile. LC–MS analysis of rice wine identified diverse non-volatile compounds, including peptides and bioactive derivatives, that affect its sensory and functional properties. The selected rice wines were stored in amber coloured bottles for the period of six months and storage studies showed good stability over the same period for both rice wines prepared using baker’s yeast and pure strain. Rice wines made with both baker’s yeast and pure strain showed increasing pH, slight rises in alcohol content and improved clarity. Total soluble solids, total sugars, total phenolic compounds and total flavonoids declined steadily over time in both treatments. Reduction in microbial colonies were also observed in both treatments. The cost of production of rice wine was in the range of ₹ 207.95/L and ₹ 216.71/L. The developed wines exhibited good organoleptic and physicochemical qualities, making them suitable for commercialisation. The developed wines demonstrated good nutritional qualities, a favourable volatile profile with moderate antioxidant activity and were also shelf stable. The utilisation of native rice varieties into wine production can unlock their economic potential and render previously underutilised varieties profitable.