> A truly new taste that doesn’t map onto the existing five basics would likely register as “off” rather than delicious. Your brain wouldn’t know what to do with it, nutritionally speaking.
We have five taste receptors, so it's it's actually impossible to get something that doesn't map unto those five. Instead, what we call the taste of food, and what GP was referring to, is actually the smell of food, or more commonly, its aroma, which we can detect both from the outside by sniffing it with our noses, and while it is in our mouths via molecules wafting up to our respiratory tract.
Unlike the simplicity of taste, we have a huge array of smell receptors, with most of them having much more indirect associations, if any, with any specific survival need. It's very much possible, and in fact quite common, to synthesize novel smells/aromas which don't resemble any natural food.