Abstract: The bacterium producing thermostable .alpha.-amylases of this invention is an anaerobic bacterium belonging to Clostridium. The thermostable .alpha.-amylases of this invention is novel .alpha.-amylases which are excellent in thermostability and acid resistance and have a slight calcium requirement. Said .alpha.-amylases are obtained by culturing the aforesaid bacteria and collecting the .alpha.-amylases from the culture. When the aforesaid .alpha.-amylase is used, sugar production process can be greatly rationalized.

Abstract: This invention relates to a process for liquefying starch. More particularly it relates to an appropriate process for liquefying starch by using a thermostable .alpha.-amylase which has an optimum working pH range in an acidic region and a low calcium requirement.This invention provides a process for liquefying starch by using a calcium-requiring, thermostable .alpha.-amylase which requires a calcium concentration of 10 .mu.m or below under a thermostable condition.In the process of the present invention, it is unnecessary to add a calcium salt in liquefying starch and the starch slurry can be reacted while remaining acidic without neutralization, so that the load at the desalting step of the product can be significantly relieved.