Je mélange la vinaigrette avant de la mettre dans la salade.

Because avant de + infinitive is the normal pattern when the same person does both actions.

• Je mélange la vinaigrette
• avant de la mettre dans la salade

So the sentence means that I do the mixing, and I also do the putting in.

If the subject changes, French usually uses avant que + subjunctive instead:

• Je mélange la vinaigrette avant que tu la mettes dans la salade.

So:

• avant de + infinitive = same subject
• avant que + subjunctive = different subject

Because after avant de, French uses an infinitive.

So:

• avant de mettre = before putting / before I put

You do not use a conjugated form like mets here.

Compare:

• Je mets la vinaigrette dans la salade. = I put the dressing in the salad.
• avant de la mettre = before putting it in / before I put it in

Here, la is a direct object pronoun meaning it. It refers back to la vinaigrette.

So the sentence is structured like this:

• Je mélange la vinaigrette = I mix the vinaigrette
• avant de la mettre = before putting it in

French often replaces a repeated noun with a pronoun, just like English does.

In French, object pronouns usually come before the verb they belong to.

So French says:

• la mettre = to put it

Not:

• mettre la ❌

This is true even with infinitives:

• Je vais la mettre = I am going to put it
• avant de la mettre = before putting it

English puts it after the verb, but French puts la before it.

Yes, absolutely.

Both are correct:

• Je mélange la vinaigrette avant de la mettre dans la salade.
• Je mélange la vinaigrette avant de mettre la vinaigrette dans la salade.

But the second version sounds more repetitive because it repeats la vinaigrette. Using la is more natural once the noun has already been mentioned.

So French prefers:

• avant de la mettre

just as English prefers:

• before putting it in

instead of repeating the vinaigrette again.

French uses articles much more often than English does. In this sentence, la vinaigrette and la salade mean the vinaigrette and the salad.

In everyday French, you usually need the article with nouns like these:

• la vinaigrette
• la salade

English sometimes leaves articles out in more general expressions, but French usually does not.

It can mean either one, depending on context.

The French present tense often covers both:

• I mix
• I am mixing

So this sentence could mean:

• a habitual action: I mix the vinaigrette before putting it in the salad
• an action happening now: I’m mixing the vinaigrette before putting it in the salad

Context tells you which meaning is intended.

Yes, sur la salade is also possible, but it gives a slightly different image.

• dans la salade = into the salad, mixed into it
• sur la salade = onto the salad, on top of it

With mettre de la vinaigrette, both can make sense, depending on whether you imagine the dressing being poured onto the salad or mixed into it. In your sentence, dans la salade suggests putting it in as part of the whole salad mixture.

Here it means salad.

French salade can sometimes refer to:

• the dish: a salad
• lettuce or salad greens, depending on context

In this sentence, because you are putting vinaigrette into it, la salade is most naturally understood as the salad dish.

Almost, yes. La vinaigrette is the oil-and-vinegar type of salad dressing.

In French, it commonly refers to a dressing made with ingredients like:

• oil
• vinegar
• mustard
• salt
• pepper

So if you already know the English word vinaigrette, the meaning is very close.