Most of the unsalted butters on grocery shelves contain "natural flavorings." What are these flavorings, and why are they added to the butter?
The “natural flavorings” found in many unsalted butters produced in this country refer mainly to a compound called diacetyl, a natural byproduct derived from culturing skim milk with bacteria, namely Streptococcus lactis. Diacetyl is used to give rich, buttery flavor to processed foods like Twinkies and movie popcorn, but in butter its purpose is merely to act as a preservative. According to Marianne Smukowski at the Wisconsin Center for Dairy Research, diacetyl can extend unsalted butter’s shelf life from 90 to 120 days. (Salted butter, on the other hand, doesn’t need such “natural flavoring,” as salt itself is a preservative.)
Just to see if there was any effect on flavor, we compared diacetyl-enhanced unsalted butter with European diacetyl-free unsalted butter. The verdict? Only a few tasters identified a mild tanginess in the former; most detected no difference between the two samples. When it comes to butter, “natural flavorings” don’t have much flavor at all.