Learn Hardcore French: Le vinaigre est fort, alors Marie met du citron pour que ce soit moins fort. - The vinegar is strong, so Marie adds lemon so it is less strong.

du = de + le. It’s the partitive article: “some/any,” an unspecified amount. So mettre du citron = “to add some lemon.”
de citron appears after quantities and negation: un peu de citron, trop de citron, pas de citron.
le citron would mean “the lemon” (a specific one) or “lemon in general” as a concept, which isn’t what we want here.

Does mettre du citron mean “add lemon juice,” or literally “put a lemon in”?

In cooking, mettre is a very common, general verb for “put/add.” Du citron is a mass noun and usually implies lemon juice in this context, but it’s a bit vague—it could also mean zest or pieces. If you want to be precise, say mettre/ajouter du jus de citron or presser du citron.

Why is it pour que ce soit and not something like pour que c’est?

Because pour que (expressing purpose: “so that”) always triggers the subjunctive. Soit is the present subjunctive of être. Using the indicative (c’est) after pour que is ungrammatical.

What exactly does ce refer to in pour que ce soit moins fort? Could I use il or ça?

ce is a neutral/dummy subject, roughly “it,” referring to the situation/taste as a whole. It’s very natural with être.
You could say pour qu’il soit moins fort if you want to refer specifically to le vinaigre.
pour que ça soit is common in speech but more informal. In writing, prefer ce.

Is ça soit correct?

Yes in informal speech: pour que ça soit moins fort. In standard/written French, prefer pour que ce soit. Both are understood; ce is stylistically safer.

How is soit formed and pronounced? Why not sois?

Subjunctive of être: que je sois, que tu sois, qu’il/elle/on soit, que nous soyons, que vous soyez, qu’ils/elles soient.
Here the subject is third‑person singular (ce), so it must be soit, not sois.
Pronunciation: soit = [swa].

Why is it fort and not forte?

Le vinaigre is masculine, so fort matches it in Le vinaigre est fort.
With ce in pour que ce soit moins fort, adjectives default to masculine singular: moins fort. Using forte there would be wrong.

Could I say moins acide or plus doux instead of moins fort?

Yes, depending on the nuance:

moins fort = less strong/pungent in taste (broad).
moins acide = less sour (specifically about acidity).
plus doux = milder/softer. All are acceptable; choose the shade of meaning you want.

Why is there a comma before alors? Could I use donc or du coup instead?

The comma is optional but common to mark the pause: …, alors …. You can also write two sentences. Alternatives:

donc = therefore (more logical/concise).
alors = then/so (neutral/narrative).
du coup = so/as a result (colloquial). All would fit with slight tone differences.

Is mettre the right verb? How do you conjugate it here?

Yes—very common in cooking for “to put/add.” Present tense:

je mets, tu mets, il/elle met, nous mettons, vous mettez, ils/elles mettent Here, Marie met is third person singular (no final -s).

Pronunciation tips for tricky words in the sentence?

du [dy] (French u, like German ü)
met [mɛ] (same sound as mets)
citron [sitʁɔ̃] (final -n makes the vowel nasal)
alors [alɔʁ]
soit [swa]
moins [mwɛ̃] (final -s silent; nasal vowel)
fort [fɔʁ] (final -t silent)

Could I use an infinitive instead of pour que? For example, pour le rendre moins fort?

Yes. Use pour + infinitive when the subject stays the same:

Marie met du citron pour le rendre moins fort. Here, Marie is the one acting in both parts. With pour que + subjunctive, you typically set a goal/result possibly affecting a different subject (or an abstract “it” with ce).

Is fort about spiciness (chili heat) here?

No. fort = strong/potent in taste or smell. For chili heat, use épicé/pimenté. For sourness, acide. Context clarifies that vinegar is “strong/sharp,” not spicy.

Why isn’t there a que after moins fort (like “less strong than”)?

You only need que if you explicitly compare two things: moins fort que le vinaigre pur. Here it just means “less strong” in absolute terms, so no que is needed.

What happens to du citron under negation?

Partitives become de after negation: Marie ne met pas de citron. (Not: ~pas du citron~.)