Have you ever been to a wine tasting, or read the copy on the back of a wine bottle? If so, then you know that wine has notes. For example, a snooty waiter may inform you, “This full-bodied Chardonnay is heralded as having notes of vanilla and citrus with a walnut finish.” This doesn’t mean that the wine is infused with vanilla, citrus fruits, or nuts. It’s just how our brains(and taste buds) interpret some advanced microchemistry.
Grape juice becomes wine through fermentation. Yeast is added to grapes and grape juice, and it eats the sugar found naturally in fruit. That, in turn, creates alcohol. Along the way, thousands of complex chemical compounds—still within the grapes—are formed. Even though those compounds are still by and large made of grapes, the molecules have been rearranged ever so slightly that they taste different from just grape juice or wine. The brain (and taste buds) interprets them as other, more familiar flavors. For example, let’s say that fermentation creates a chemical compound that has a similar structure to that of apples. Even though the wine is made of grapes, the taste buds will taste that chemical compound, even just a little bit, because the
molecules in that compound are arranged like an apple molecule.
Source: Do Geese Get Goosebumps? By The bathroom Readers Institute