Manufacturers produce corn syrup by removing cornstarch from the grains of corn and using acid hydrolysis to convert the starches to dextrose, a simple sugar that is less sweet than table sugar. Further refining with enzymes converts more of the dextrose to fructose, producing high fructose corn syrup.
To create cornstarch, the manufacturer places over 150,000 pounds of corn kernels in a large vat with warm water and sulfur dioxide to soften the husk. The softened corn passes through a machine to remove the germ from the starch. The pulp passes through more mills to remove the fiber and protein. At the end of the process, the product is 99.5 percent pure cornstarch.
Corn syrup manufacturers mix the cornstarch liquid with acids and heat the mixture to convert the starch. Once they complete the conversion, they filter the syrup to remove impurities. Heating the syrup removes some of the water to create the corn syrup available on grocer's shelves. Further evaporation of the water produces corn syrup solids, that other processes use as a sweetener.
Some manufacturers require a sweeter product than is available with dextrose of normal corn syrup. Corn syrup manufactures add an enzyme to convert the syrup to the sweeter dextrose for use in soft drinks and other finished products.