One of St. Thomas’s account of beauty is “what pleases when seen”. There is a question whether “seen” is used in its general meaning where it can stand for any act of sensation (viz. “see how it tastes” or “see how it smells”) or as meaning a more powerful cognitive power. De Anima II.9 is instructive here:
Smell and its object are much less easy to determine than what we have hitherto discussed; the distinguishing characteristic of the object of smell is less obvious than those of sound or color. The ground of this is that our power of smell is less discriminating and in general inferior to that of many species of animals; men have a poor sense of smell and our apprehension of its proper objects is inseparably bound up with and so confused by pleasure and pain, which shows that in us the organ is inaccurate. It is probable that there is a parallel failure in the perception of color by animals that have hard eyes: probably they discriminate differences of color only by the presence or absence of what excites fear, and that it is thus that human beings distinguish smells.
While it makes sense to call things seen or heard beautiful, it seems odd to speak of beautiful smells or tastes. So how are we to take this?
One approach is to take this as a denial of beauty as a transcendental. There is nothing odd in speaking of things that taste good or have a good scent, nor is there anything odd in using any sense as a standard for truth, like smelling that there is a gas leak in the kitchen. Beauty does not convert with being, but with something more refined and set apart, and which can only arise or be seen through greater cognitive precision.
Another approach is to say that beauty is transcendental, but that imprecision in the cognitive power leads to imprecision in beauty. All we can mean by a beautiful smell is a pleasant one, but the pleasant counts as beautiful. We might say more than this: the various characteristics of beauty, like proportion, might apply to the balance of the ingredients or elements in the taste of something.
I lean towards the idea that tastes, scents and the tactile are not beautiful. Calling even a perfect wine “beautiful” seems forced or metaphorical, and calling a disgusting smell “ugly” doesn’t seem to amount to anything more than calling it “bad”. Taken in this way, beauty just collapses into the goodness.
Notice that everything turns on the idea of whether the pleasant as pleasant is beautiful. Given the pleasant as such is good, and beauty is distinguished from goodness, it seems as though we should say no. Said another way, to call something pleasant suffices to call it a good, but it does not suffice to call it something beautiful. The same case can be made from a consideration of what is useful. Beauty requires a higher mode of objectivity – mere subjective agreement or fittingness does not suffice, still less does mere usefulness for some task. There is a sort of goodness that is not based purely on the object, but on its relation to the subject, which is why subzero temperatures are good for polar bears and feces smells good to flies and dung beetles.
Beauty therefore is divided from goodness by its greater degree of objectivity. There is no subjective beauty, and to the extent we say there is we are only speaking about goodness (specifically, what is pleasant or useful.) The account of beauty as “what pleases when seen” gives an elemental account of its genus and difference: it is what is agreeable to a cognitive power precisely because of that power has a degree of perfection that allows for a pure objectivity, and not just a subjective relation to the cognitive power.