Se a manga estiver madura, eu vou fazer suco.

Se means if, so it introduces a condition: the juice will be made only in the case that the mango is ripe.

• Se a manga estiver madura... = If the mango is ripe...
• Quando a manga estiver madura... = When the mango is ripe...

Using quando sounds more certain, as if the mango is expected to become ripe sooner or later. Using se keeps it conditional.

After se referring to a future possibility, Portuguese normally uses the future subjunctive.

So:

• Se a manga estiver madura = If the mango is ripe / if the mango turns out to be ripe

Not:

• Se a manga está madura ❌ in this kind of future condition

This is a very common pattern in Portuguese:

• Se eu tiver tempo, eu vou.
• Se ele puder, ele vem.
• Se chover, ficamos em casa.

English usually just uses the present after if, but Portuguese often uses the future subjunctive.

Estiver is the future subjunctive form of estar.

Here are some forms of estar for comparison:

• está = present indicative, is
• esteve = preterite, was
• estiver = future subjunctive, used in clauses like if/when something may happen in the future

In this sentence, estiver does not mean a separate tense like English will be. It is just the form Portuguese uses after words like se when talking about a future condition.

Portuguese usually uses estar for a condition or state that can change, and ripeness is a changing condition.

• A manga está madura = The mango is ripe
• A manga está verde = The mango is unripe / green

Ripeness is temporary and changes over time, so estar is the natural choice.

Madura agrees with manga, which is a feminine noun in Portuguese.

• a manga
• madura

Adjectives usually match the noun in gender and number:

• a manga madura
• o abacate maduro
• as mangas maduras
• os abacates maduros

So madura is feminine singular because manga is feminine singular.

No. Manga can also mean sleeve.

So depending on context:

• a manga da camisa = the sleeve of the shirt
• a manga está madura = clearly the mango is ripe

In this sentence, madura and fazer suco make it obvious that manga means the fruit.

Portuguese uses definite articles much more often than English.

So a manga can mean:

• the mango
• sometimes even mango in a general/specific context, depending on situation

In this sentence, a manga likely refers to a specific mango already understood from context.

Using uma manga would mean a mango, introducing it less specifically.

Both are possible, but eu vou fazer is much more common in everyday Brazilian Portuguese.

• eu vou fazer suco = natural, conversational
• farei suco = correct, but often sounds more formal, written, or less common in speech

Brazilian Portuguese very often uses ir + infinitive to talk about the future:

• vou comer
• vamos sair
• ela vai chegar

So this sentence sounds very natural.

Yes. Portuguese often allows the subject pronoun to be omitted when the verb already shows who the subject is.

So both are correct:

• Se a manga estiver madura, eu vou fazer suco.
• Se a manga estiver madura, vou fazer suco.

Including eu can add clarity, emphasis, or simply reflect a speaker’s style. In Brazilian Portuguese, subject pronouns are used more often than in some other varieties, so eu sounds perfectly normal.

Both can be correct, but they mean slightly different things.

• fazer suco = make juice, in a general sense
• fazer o suco = make the juice, referring to a specific juice already known in context

In this sentence, fazer suco sounds more natural because it just means making mango juice generally, not a particular previously mentioned juice.

Yes. Portuguese often leaves that understood from context.

Since the sentence says:

• If the mango is ripe, I’m going to make juice

the listener naturally understands it means juice from the mango, unless context suggests something else.

If someone wanted to be extra explicit, they could say:

• vou fazer suco de manga

But it is not necessary here.

Yes. Portuguese allows some flexibility.

The original sentence:

• Se a manga estiver madura, eu vou fazer suco.

You could also say:

• Eu vou fazer suco se a manga estiver madura.

Both are natural. The first version puts the condition first, which is very common and often sounds slightly more organized or emphatic.

Yes, in some contexts. That can sound like a habitual action or a more immediate, less explicitly future statement.

Compare:

• Se a manga estiver madura, eu vou fazer suco.
  Clear future plan: I’m going to make juice.

• Se a manga estiver madura, faço suco.
  Can mean I’ll make juice in a more informal way, or sometimes I make juice as a usual reaction.

For learners, eu vou fazer suco is the safest and clearest way to express the future here.