Each independent variable
was tested at three levels, a low (−1), a medium (0) and a high
(+1) level. The four factors’ three levels were sucrose concentration
(A): 5%, 12.5% and 20%; SSW concentration (B): 5%, 12.5% and 20%;
inoculum size (C): 5%, 10% and 15%; and fermentation time (D):
2 days, 4.5 days and 7 days