As it turns out, there is a discernible difference between the two varieties of Oreos. Or, rather, there are two key differences. Per Shop Oreo, classic Oreos list artificial flavoring among their ingredients. The Costco variety lists natural flavoring instead (via Costco). Likewise, classic Oreos utilize high-fructose corn syrup in their recipe, while Costco Oreos are sweetened with invert sugar instead. According to Science of Cooking, invert sugar is a mixture of glucose and fructose that retains moisture, reducing crystallization, and producing a smoother feel in your mouth.
Quora notes that the recipe for classic Oreos has changed multiple times over the years, from the introduction of high-fructose corn syrup to the removal of lard and trans fats. That means their taste has understandably changed since they were first introduced to the market all the way back in 1912, as has ours, as a population. However, if you're chowing down on a whole pack of Costco Oreos and feeling less like you're living your best life than when you gorge on a pack of classics, don't feel bad, your taste palette is simply too accustomed to the brand-name variety.
