This one is always a little tricky since we tell students that non-action verbs like smell, see, taste, hear, and feel are not possible with the present progressive, but then other senses of the verb are still possible. You can't say "I'm seeing a bird out my window!" but you can say "I'm seeing someone" (i.e. I'm dating someone). Ron Cowan's amazingly thorough The Teacher's Grammar of English describes four exceptions to the "no ING-verb with non-action verbs" rule:

Exception #1: To add more intensity of emotion

Remodeling my house is really costing me a lot of money!

Exception #2: To describe a sudden change in behavior

You are being so horrible today! (Normally, you're a fine chum, but today you're a royal jerk!)

Exception #3: To describe a change in condition

His guitar playing is sounding better and better every day! (he's learning guitar, and it's getting better)

Exception #4: To make something more polite

We were hoping you could explain the problem. (We hope you can explain the problem is a bit more forceful)

Tricky, tricky!

Anyway, if you don't have a copy of Cowan's Grammar, you really should get one. I resented my professor for the fact that we didn't use this book too much in class, but I am still referring to that book in teaching any thorny issues.

All things aside, it conjures up a pretty funny picture if you say the soup is smelling.