Comma placement in a sentence like "A small but juicy fruit."?

Solution 1:

You might think it should be:

(It was) a small, but juicy, fruit.

It need not be so.

But is a conjunction, and when used to join two standalone sentences, you "should" put a comma before it.

Drink is the curse of the land. It makes you fight with your neighbor. It makes you shoot at your landlord, but it makes you miss him.

Your use of but doesn't join two separate sentences. So you have actually punctuated it perfectly:

(It is) a small but juicy (tropical) fruit.

If you added adjectives which did not modify each other, you might need a comma:

It was a small but heavy, juicy tropical fruit. But some people would not use a comma there.