Bioethanol concentration
Ethanol concentration was determined according to the method of Williams and Darwin (1950). The 100 ml of potassium dichromate reagent solution was prepared by dissolving 1 g of potassium
dichromate in concentrated (6N) sulfuric acid. The prepared solution was shaking for homogeneity of mixture solution. On the other hand, saturated s-Diphenylcarbazide solution was prepared by dissolving 1 g of s-Diphenylcarbazide to 1 ml of 95% ethanol and the supernatant was collected. The 1 ml of ethanol solution was added to the glucose sample into the capped test tube. The test tube was covered with a piece of paraffin film to avoid the loss of liquid due to evaporation. The mixture was then heat up using water bath at 90°C for 5 to 15 min until it looks like red-brown color. The
mixture was then added with 1 ml of a 40% potassium sodium
tartrate (Rochelle salt) solution to stabilize the color. The ethanol
absorbance values were measured at 575 nm after cooling to room
temperature in a cold water bath.