The enzyme a-amylase digests the starch to produce soluble dextrin molecules; this is called liquefaction. Small quantities of liquefied starch are spray-dried for use in baby foods and as bulking agents.

Liquefied starch is rapidly cooled to 60°C, pH adjusted to 4.0-4.5, and glucoamylase is added at 0.65-0.81/ton (200 U/kg). Generally, a debranching enzyme, e.g., pullulanase from Bacillus acidopullulyticus, is also added at 100 U/kg to digest branched oligosaccharides, which increases the DE of syrup to 98-99.

Glucoamylase is generally obtained from Aspergillus Niger. The mixture is incubated for 72 h, heated to 85°C to stop the reaction, cooled and filtered. Further purification may be done by using activated charcoal and ion exchange resins. The syrup composition is typically as follows: 95­97% glucose, 1-2% maltose and 0.5-2% isomaltose.

Generally, starch liquefaction is a continuous process, while) saccharification is done in batch mode in large stirred tanks. Continuous saccharification is possible but at least 6 tanks will have to be used in a series.