The presently disclosed subject matter provides a process for starch liquefaction using at least two classes of .alpha.-amylase enzymes, wherein the starch hydrolysis pattern from at least two of these classes is different. At least one class of enzyme is provided to the liquefaction process in the form of transgenic plant material expressing at least one class of a-amylase enzyme or is provided in the form of a purified or partially-purified .alpha.-amylase enzyme preparation. The second or subsequent class(es) of .alpha.-amylase enzymes may be provided in the form of additional transgenic plant material expressing the second or subsequent class(es), or may be provided in the form of a second or subsequent purified or partially-purified .alpha.-amylase enzyme preparation.