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 crystallisation and enhance flavour.
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.
High-fructose corn syrup (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.
Golden syrup can be used as a substitute for corn syrup.