According to neuroscientist Camilla Arndal Andersen, how consumers describe the taste of food can be misleading largely due to inherent biases. Among the most problematic is the “courtesy bias,” which comes into play when people respond with what they see as a socially acceptable opinion that doesn’t accurately reflect how they feel. There’s also the “bias blind spot,” in which we think we’re less biased than others. In short, we’re biased about our biases.

We see the courtesy bias at work in the wine industry when consumers say they prefer dry wines but, when given a choice, favor wines that are off dry or have much higher levels of residual sugar. Arndal Andersen points out that even trained tasters aren’t immune to bias; for example, foods that contain vanilla are rated sweeter by professionals even if they lack sugar. This can be explained by our long association between the two ingredients, which is based on a lifetime of exposure to their use in baked goods and desserts.

As one of the few low-threshold odors we still find pleasant even past the point of overexposure, vanilla—aka 4-hydroxy-3-methoxybenzaldehyde—is known to have 170 volatile compounds, of which vanillin is dominant. The vanilla flavor wheel used by the flavoring company FONA International specifies 29 distinct flavor characteristics for natural vanilla that it groups into ten main categories: smoky, spicy, botanical, sulfury, sweet, creamy, medicinal, cooked, fatty, and floral.  

Like wine grapes, natural vanilla grows in different places—among them Madagascar; Mexico, where it originated; or Tahiti—and has different taste profiles and potency. For example, Madagascar vanilla, typically called Bourbon vanilla, is highly sought after for its rummy taste and sweet aroma.

The demand for vanilla flavoring, however, has long exceeded the supply of vanilla beans. Natural and synthesized vanillin are used to create the impression of sweetness in foods, as seen in the mass-market chocolate industry’s practice of adding synthetic vanillin to products to counter the bitterness of cocoa. With the growth and popularity of the sweet red blend category, it’s no surprise to find that vanilla/vanillin is a dominant flavor descriptor for this style, as it undoubtedly helps mask bitterness imparted by tannins.

When tasting across a commercial-quality range of single-varietal, and blended red wines from California for a recent sensory project, the use of vanillin-flavored oak alternatives left a ubiquitous stamp across all brands and varieties tasted. While the organic polymers known as lignins that are present in oak serve as one source of vanillin, few consumers know that an estimated 85% of the world’s supply of synthetic vanillin is derived from petroleum or crude oil. (The other 15% comes from the manufacture of cellulose.)

As for the perception of sweetness that vanillin can contribute to red wines, while we may be aware of unconscious biases, there’s little scientific evidence that supports the idea that heightened awareness will reduce the occurrence of bias in general. In other words, it’s very likely that we’ll still perceive vanillin-dominant red wines as tasting sweeter.