How corn syrup is made

Enzymes chop corn starch into glucose, and a second enzyme can bend part of it into sweeter fructose.

stations: 6
things upstream: 3
raw sources: 2
steps from the ground: 2

The short version

Corn is wet-milled to pull out the starch. Then enzymes do the work. One breaks the starch into short chains, another snips those chains into single glucose units, and the resulting liquid is filtered and evaporated to a thick syrup. A third enzyme can turn part of the glucose into sweeter fructose.

Wet-mill the corn

Number 2 yellow dent corn is soaked and ground, and its starch is washed free of germ, fiber and protein. The result is a milky starch slurry.

Goes in
Corn
Chop with bacterial enzyme

Starch is mixed with water and the enzyme alpha-amylase, which comes from Bacillus bacteria grown in a fermenter. It cuts the long starch molecules into shorter chains called oligosaccharides.

Goes in
Corn starch Water
Snip into glucose

A second enzyme, glucoamylase from the fungus Aspergillus, removes glucose units from the ends of the short chains. How far this reaction runs sets the syrup's dextrose equivalent. Less reaction makes a thicker, less sweet syrup, and more makes a thinner, sweeter one.
Filter and decolorize

The sweet liquid is filtered to remove protein and fat, then passed over carbon and ion-exchange resin to take out color and salts.
Evaporate to syrup

Vacuum evaporators boil off water until the liquid is thick and about one third glucose by weight in the common grades. Light corn syrup is seasoned with vanilla and salt, and dark corn syrup has refiner's syrup, caramel color and flavor added.
Convert some to fructose

For high-fructose corn syrup, the glucose syrup is run through columns packed with the enzyme D-xylose isomerase. Part of the glucose rearranges into fructose, and the result is sweeter and dissolves better.

End of the lineCorn syrup Next it goes into gummy bears, marshmallow, jelly beans and 11 more.

Worth repeating

It takes about 60 bushels of corn to make one short ton of glucose syrup.
The first corn syrup was made in 1811 by boiling starch with hydrochloric acid, and enzymes took over later.