Process standardization, characterization and storage study of a sweet potato (Ipomoea batatas L.) wine

An investigation was undertaken to identify the best fermentation process parameters for the production of wine from reconstituted sweet potato (Ipomoea batatas) juice and study the effect of storage period and temperature on sensory and optical attributes of wine. The extracted sweet potato juice was first treated with crude amylase solution at 5% v/v to hydrolyze the starch into fermentable sugar. It was further reconstituted by adding distilled water, 60% sucrose syrup and 0.1M oxalic acid at different concentrations to attain samples of final total soluble solids concentration (TSS) and pH in the range of 18 - 30°Brix and 4.0 - 5.5, respectively. All the samples were fermented at 20 - 35°C with inoculums size of 8 - 14% (v/v) till TSS and ethanol percentage remained constant for three consecutive days. The reconstituted juice with initial TSS content of 22oBrix and pH of 4.5, fermentation process temperature of 25ºC and inoculum size of 10% (v/v) for the fermentation period of 240 h produced wine with highest ethanol percentage of 9.6. The titratable acidity, total sugar, reducing sugar and TSS of the wine were 0.83 g/100 g, 1.84 g/100 g, 1.65 g/100 g and 3.15°Brix, respectively. Color of the wine was observed to be yellowish white with little transparency. The pH of the wine was 3.73 and it was slightly higher than the generally acceptable limit. Sensory evaluation revealed that the wine had a very good taste and aroma with good body. The wine also had acceptably good after-taste and color. The changes in total color difference (ΔE) and browning index of the wine were prominent during storage. The longer storage period at lower temperature resulted in the stability of changes in ΔE and browning index of the wine.