Corn syrup is made by heating corn starch along with an acid or malt enzyme. During this process, the long chains of glucose molecules in the starch are broken apart into individual glucose molecules, which our tongues taste and perceive as sweet. This process was actually developed in the early 1800's using potato starch and wasn't applied to corn starch until later in the century.
High-fructose corn syrup was developed in the 1960's, almost a century later. This syrup undergoes an additional enzymatic process that converts some of those glucose molecules into fructose. This is the sweetest of all the sugar molecules and makes corn syrup equally as sweet as table sugar.
The key thing to understand is that not all corn syrup is high-fructose, and it's the high-fructose version that is the primary subject of debate. It's possible to find regular corn syrup to use in your own cooking and candy-making, though it might take some searching. Karo, the most popular supermarket brand of corn syrup, is unfortunately high-fructose.
Does anyone know a good brand of regular corn syrup available on the market?
(Image: Emma Christensen for the Kitchn)