Corn syrup is a syrup, made using cornstarch as a feedstock, and composed mainly of glucose. A series of two enzymatic reactions are used to convert the corn starch to corn syrup. Its major uses in commercially-prepared foods are as a thickener, sweetener, and for its moisture-retaining (humectant) properties which keep foods moist and help to maintain freshness.
Corn syrup is used to soften texture, add volume, prohibit crystallization and enhance flavour. Because cane sugar quotas raise the price of sugar in the United States, domestically produced corn syrup and high-fructose corn syrup are a less expensive alternative often used in American-made processed and mass-produced foods, candies, and sodas to help control costs.
The more general term glucose syrup is often used synonymously with corn syrup, since the former is most commonly made from corn starch. Technically, glucose syrup is any liquid starch hydrolysate of mono, di, and higher saccharides and can be made from any sources of starch; wheat, rice and potatoes are the most common sources.
Glucose (or dextrose) syrup is produced from number 2 yellow dent corn. When wet milled, approximately 2.3 litres of corn is required to yield an average of 947g of starch, to produce 1kg of glucose (or dextrose) syrup (a bushel of corn will yield an average of 31.5 pounds of starch, which in turn will yield about 33.3 pounds of syrup). Thus, it takes about 2,300 litres of corn to produce a tonne of glucose syrup (or 60 bushels of corn to produce one short ton).
The viscosity and sweetness of the syrup depends on the extent to which the hydrolysis reaction has been carried out. To distinguish different grades of syrup, they are rated according to their "dextrose equivalent" (DE).
Glucose syrup was the primary corn sweetener in the United States prior to the expansion of High-fructose corn syrup (HFCS) production. HFCS is a variant in which other enzymes are used to convert some of the glucose into fructose. The resulting syrup is sweeter and more soluble. Corn syrup is also available as a retail product. The most popular retail corn syrup product in the United States is Karo Syrup, a fructose/glucose syrup.