Corn syrup comes from the starch inside ordinary field corn kernels. The starch is extracted through an industrial process called wet milling, then broken down into simple sugars using enzymes. The result is a thick, sweet liquid that shows up in everything from candy and baked goods to soft drinks and salad dressings.
From Kernel to Starch
A corn kernel is roughly 70% starch by dry weight, but that starch is locked up with fiber, protein, and oil. Getting it out requires a process called wet milling, which systematically separates each component.
The kernels first soak in warm water for 24 to 48 hours to soften them. This loosens the outer hull and swells the starch granules inside. From there, the softened corn is coarsely ground and sent through a series of separation steps. The oil-rich germ floats to the top in spinning hydrocyclones (essentially high-speed centrifuges that sort materials by density) and gets skimmed off for corn oil production. The remaining slurry passes over fine screens that catch the fibrous hull pieces while letting the starch and protein wash through. Finally, centrifuges separate the protein from the starch based on their different densities. The isolated starch goes through 12 stages of washing to remove any remaining impurities.
Each byproduct has its own market. The germ becomes corn oil. The protein fraction, called corn gluten meal, is sold as animal feed. The fiber goes into livestock feed as well. Nothing from the kernel goes to waste.
How Enzymes Turn Starch Into Syrup
Corn starch is a long chain of glucose molecules bonded together. It doesn’t taste sweet because your taste buds can’t detect those large molecules. To make syrup, manufacturers have to chop those chains into shorter pieces and, ultimately, into individual glucose molecules.
This happens in two stages. First, the starch is mixed with hot water and heated to around 95°C (about 200°F). A heat-stable enzyme is added that rapidly cuts the long starch chains into medium-length fragments. This step, called liquefaction, turns a thick paste into a thinner liquid within about 30 minutes. The mixture is then cooled to around 60°C (140°F), and a second enzyme finishes the job by snipping those fragments into individual glucose units. This second step is called saccharification.
In 1811, a Russian chemist named Gottlieb Kirchhoff first demonstrated that starch could be converted to sugar using sulfuric acid and heat. Modern production replaced that harsh acid approach with precisely targeted enzymes, which are faster, more controllable, and don’t leave chemical residues in the final product.
Different Grades of Corn Syrup
Not all corn syrup is broken down to the same degree. The industry measures this using something called dextrose equivalent, or DE, which is essentially a scale from 0 to 100. Pure unbroken starch scores 0, and pure glucose scores 100. The higher the number, the sweeter and thinner the syrup.
Two grades dominate the market: a medium grade at 42 DE and a high grade at 65 DE. The 42 DE version retains more of those medium-length starch fragments, giving it a thicker body and milder sweetness. It’s favored in foods where you want moisture retention and smooth texture without overpowering sweetness. The 65 DE version is sweeter and more fluid, closer to the taste of pure sugar.
Light Corn Syrup vs. Dark Corn Syrup
The bottles of corn syrup you see in grocery stores come in two varieties, and the difference is simpler than you might expect. Light corn syrup is nearly clear and flavored with just vanilla and salt. Dark corn syrup gets its deep brown color and richer, more complex flavor from added refiner’s syrup (a byproduct of sugar refining similar to molasses), caramel color, salt, and a small amount of the preservative sodium benzoate. Neither version contains high-fructose corn syrup.
Light corn syrup works well in recipes where you want sweetness without a strong flavor, like pecan pie filling or homemade caramel. Dark corn syrup adds a deeper, almost bittersweet note that pairs well with gingerbread, barbecue sauces, and baked beans.
How High-Fructose Corn Syrup Is Different
Regular corn syrup is mostly glucose. High-fructose corn syrup, or HFCS, goes through one additional step. A third enzyme converts some of that glucose into fructose, a different sugar that tastes noticeably sweeter. This reversible conversion is called isomerization, and it produces a syrup that mimics the sweetness profile of table sugar more closely than plain glucose syrup does.
HFCS comes in two main formulations. HFCS-42 contains about 42% fructose and is used in processed foods like cereals, sauces, and condiments. HFCS-55 contains about 55% fructose and is the standard sweetener in soft drinks. For comparison, regular table sugar is 50% fructose and 50% glucose, so HFCS-55 is only slightly higher in fructose content. The economic advantage of HFCS is that corn is cheaper and more abundant in the United States than sugarcane, making it a lower-cost sweetener for large-scale food manufacturing.
Purification and Finishing
Raw corn syrup straight from the enzymatic process contains dissolved minerals, organic acids, and compounds that give it off-colors and unwanted flavors. Before it’s sold, the syrup passes through an ion exchange system, where charged resins pull out salts and acidic impurities the way a magnet pulls iron filings from sand. A separate cation process removes positively charged impurities, while an anion process removes negatively charged ones.
After ion exchange, the syrup flows through an additional polishing step using an adsorbent resin bed. This catches remaining organic compounds that contribute to discoloration and off-tastes. The finished product is a clean, clear, shelf-stable liquid. Because corn syrup has very low water activity (meaning there isn’t much available moisture for bacteria to use), it resists spoilage and lasts a long time in your pantry without refrigeration.