There is no such thing as a natural corn syrup pressed directly from corn kernels. Instead, the pulpy middle layer called cornstarch is first separated from the outer husk and the inner germ layers. The cornstarch is then stored in giant vats, where natural enzymes are added to break it down into glucose. It is these sugars which are heated and turned into what we call corn syrup.

Corn syrup is almost exactly as sweet as the granulated sugar (sucrose) it often replaces in recipes. Corn syrup can be naturally light in color which is often used in candymaking or darker which is usually used for general baking purposes. The light form of corn syrup may have vanilla flavoring added, while the dark corn syrup has a stronger natural flavor. The advantage of corn syrup over sugar is its resistance to crystallization. A candy lollipop made with corn syrup will retain its smooth texture, while a similar treat made from pure sugar may turn into a hardened rock candy. Corn syrup also prohibits crystal formation when sugar is added to a cake or fudge mixture.

Light and dark corn syrup both have a balance of dextrose, fructose, malt and glucose to keep them chemically stable, although corn syrup does have a limited shelf life compared to other sweeteners. The most controversial form of corn syrup, however, is rarely sold directly to consumers, although it can be found in a majority of processed foods sold in grocery stores. Welcome to the world of high fructose corn syrup.

High fructose corn syrup is subjected to additional processes as compared to regular corn syrup. First, three types of enzymes (alpha-amylase, glucoamylase, and glucose-isomerase) are successively added to change the starch to glucose and then fructose. Pure glucose is then added to the mixture to create some ratio of fructose to glucose which comprises the final product — high fructose corn syrup. There are various fructose-glucose ratios in high fructose corn syrup, including 90-10, 42-43, and 55-45. Since the United States Department of Agriculture subsidizes corn production but taxes imported sugar, high fructose corn syrup has become the default sweetener in many consumer food products.

High fructose corn syrup manufacturers insist that their product is just as healthy as the sucrose sugar it replaces in soft drinks, plus the savings in taxes keeps domestic food prices low. Opponents of high fructose corn syrup point to studies indicating serious health problems in laboratory rats fed a constant diet of high fructose corn syrup. Other sugars like sucrose can be processed by every cell in the human body, but fructose must be broken down in the liver. Over a lifetime, the liver may become overworked by a diet heavy in fructose.

Some say it's a matter of economics, while others point to the domestic corn industry as having a near-monopoly on the commercial sweetener market in the United States. Other countries such as Mexico still use sucrose sugar in their processed food products, so those who feel uneasy about the health effects of high fructose corn syrup should read the labels of imported foods for the word 'sugar'.