When to use, "al?"
How come it is, "bistecca al pepe," for a peppered steak, but sour juice is simply, "succo acido?" Another example, "creme al cioccolato" is chocolate cream but then sweet food is, "cibo dolce." When do you use "al" in describing things and when do you not?
The use of "al" has to do with flavoring. La torta al cioccolato [chocolate flavored cake]..."bistecca al pepe" [steak that has been flavored with pepper]. The others are adjectives describing the actual item. "How is the juice? It is sour." "How is the food?" "The food is sweet". With flavors, you wouldn't say "how is the cream? The cream is chocolate." Because chocolate is a flavor, not a description of the food. But I like viaggiatore's suggestion of recognizing nouns as flavors and adjectives as descriptors.