And then on top of that you have strains of yeast that are specifically bred to produce large amounts of both, such as the yeast strains used in Hefeweizen (German-style wheat beer; specifically, the cloudy kind that still contains the yeast sediment) [yes, I know you know this, but I'm explaining for the wider audience].
In fact, the main difference between German-style and American-style wheat beers is that German-style examples have lots of banana esters and clove phenols, while American-style examples don't. The sole reason for the difference is the strain of yeast used.
And it's not just a wheat beer thing: in general, American yeast strains are bred to produce cleaner fermentations than European strains. The distinct flavors of English and especially Belgian beers are due to the fermentation byproducts produced by the local yeast.
Homebrewer here as well. There's plenty of chemical compounds that yeast produce that give various notes that kind of resemble something else. For instance aldehydes (notably acetaldehyde) is a yeast byproduct that gives off a "green apple" flavor. Usually in beers this is considered a flaw, but I notice that some wines promote that aspect as positive if it's not overwhelming.
Diacetyl is another one -- this has a "buttery" flavor. This is considered a flaw in some styles, but is naturally present in others (English ales notably often have a little bit of this in it). Some wines are very "buttery", I understand in particular those that use a process called malolactic fermentation (where diacetyl is a byproduct) are prone to it.
From what I can Google you can get chocolate notes in wine either from the tannins in grapes, or the charring process used on barrels. However, I haven't been able to Google specific chemicals. In beer, "chocolate notes" can come from some of the toasted / roasted malts out there (IMHO more on the pale end of the "chocolate malt" spectrum -- darker "chocolate malts" taste more "coffee" like to me).
A fair bit of places offer a "off flavor" kit for beers that allow you to train your tastebuds on at least the common "faults".
On an extreme side of "off flavors," a friend of mine "scientifically" brewed a few 1gal batches to see what happens when you don't follow the rules: one fermented in the heat of the summer, one without proper sanitization (except for the bottles), one he spat in, and one he dropped a few dog hairs in.
In fact, the main difference between German-style and American-style wheat beers is that German-style examples have lots of banana esters and clove phenols, while American-style examples don't. The sole reason for the difference is the strain of yeast used.
And it's not just a wheat beer thing: in general, American yeast strains are bred to produce cleaner fermentations than European strains. The distinct flavors of English and especially Belgian beers are due to the fermentation byproducts produced by the local yeast.
I love beer chemistry.