Learn French: J'aime beaucoup le jus d'ananas. - I really like pineapple juice.

When a noun describes the flavor or main ingredient of another noun, French simply uses de (or d' before a vowel) without an article. Just like apple juice is jus de pomme, pineapple juice is jus d'ananas.

Why do we use le before jus? Isn't juice uncountable?

When you use verbs of preference like aimer (to like), adorer (to love), or détester (to hate), you always use the definite article (le, la, les) to talk about the noun in a general sense. If you were actually drinking juice right now, you would use the partitive article for uncountable things: Je bois du jus (I am drinking some juice).

Why is beaucoup placed right after the verb instead of at the end of the sentence?

In English, you might say I like pineapple juice a lot, putting the adverb at the end. In French, short adverbs like beaucoup must be placed immediately after the conjugated verb. Saying J'aime le jus d'ananas beaucoup is grammatically incorrect.

Doesn't beaucoup mean a lot? Why is it translated here as really like?

You are right that beaucoup translates directly to a lot, but aimer beaucoup is the most natural, standard way to say to really like something in French. While you could technically say j'aime vraiment, native speakers strongly prefer j'aime beaucoup for this meaning.