O mamão e o abacaxi estavam maduros, mas a casca da pera ainda era difícil de tirar.

Portuguese uses definite articles much more often than English. In this sentence:

• o mamão = the papaya
• o abacaxi = the pineapple
• a casca da pera = the skin/peel of the pear

Even when English might say just papaya or pineapple, Portuguese often prefers the article.

Also, da pera is a contraction:

• de + a pera = da pera

So a casca da pera literally means the peel of the pear.

Both are possible in some contexts, but using the articles sounds very natural and specific in Portuguese.

• o mamão e o abacaxi points to particular fruits being discussed
• mamão e abacaxi can sound more general, like talking about those fruits as categories

In everyday Brazilian Portuguese, repeating the article before each noun in a list is very common.

Because maduros agrees with o mamão e o abacaxi, which together form a masculine plural subject.

Agreement works like this:

• mamão = masculine singular
• abacaxi = masculine singular
• together = masculine plural
• so the adjective becomes maduros

Compare:

• O mamão estava maduro. = The papaya was ripe.
• O mamão e o abacaxi estavam maduros. = The papaya and the pineapple were ripe.

Because the subjects are different:

1. O mamão e o abacaxi = plural
   so the verb is estavam

2. A casca da pera = singular
   so the verb is era

So:

• estavam agrees with mamão e abacaxi
• era agrees with casca

Portuguese often uses different verbs depending on the type of description.

estar maduro

For the fruits, ripe is seen as a condition or state, so estar is natural:

• estavam maduros = were ripe

ser difícil

For difficult, Portuguese often uses ser when describing something as being inherently or generally difficult in that situation:

• era difícil de tirar = was difficult to remove

So this contrast is normal:

• estar + adjective for a temporary state
• ser + adjective for a characteristic or evaluation

Casca is a broad word for an outer covering. Depending on the context, it can mean:

• skin
• peel
• rind
• shell

Here, with pera, the best translation is usually skin or peel.

Examples:

• casca da banana = banana peel
• casca da laranja = orange peel
• casca do ovo = eggshell

Because the sentence is specifically talking about removing the skin/peel, not removing the pear itself.

• a pera era difícil de tirar would sound odd, because it suggests the pear was difficult to remove
• a casca da pera era difícil de tirar clearly means the pear’s peel was hard to take off

So casca is necessary to express the right idea.

De tirar means to remove, to take off, or to peel off, depending on context.

In difícil de tirar, the structure is:

• difícil = difficult
• de + infinitive = to do something

So:

• difícil de tirar = difficult to remove / hard to peel off

This is a very common Portuguese pattern:

• fácil de entender = easy to understand
• difícil de fazer = hard to do
• bom de comer = good to eat

In standard Portuguese, difícil de tirar is the normal form here.

• era difícil de tirar = correct and natural

Without de, it would usually sound incomplete or unnatural in this kind of sentence.

Portuguese often needs de after adjectives before an infinitive:

• fácil de usar
• difícil de encontrar
• impossível de esquecer

Ainda means still here, and placing it before the verb is very natural in Portuguese:

• ainda era difícil = was still difficult

You can sometimes move ainda around, but ainda era sounds very normal and neutral.

Compare:

• A casca da pera ainda era difícil de tirar.
• A casca da pera era ainda difícil de tirar. → less natural

So the given word order is the one learners should copy.

You could say difícil de tirar da pera, but it is usually unnecessary because a casca da pera already tells you what is being removed and from what.

• a casca da pera = the pear’s peel
• difícil de tirar = hard to remove

The sentence is already clear. Repeating da pera would sound heavier unless you wanted extra emphasis or clarification.

Yes, in normal usage:

• o mamão = masculine
• o abacaxi = masculine
• a pera = feminine
• a casca = feminine

Grammatical gender in Portuguese must be learned with the noun, because it affects:

• articles: o / a
• adjectives: maduro / madura
• some pronouns and determiners

It is best to memorize nouns with their articles:

• o mamão
• o abacaxi
• a pera
• a casca

It would be:

• O mamão e o abacaxi estão maduros, mas a casca da pera ainda é difícil de tirar.

Changes:

• estavam → estão
• era → é

So:

• past: were ripe / was difficult
• present: are ripe / is difficult

A simple pronunciation guide:

• mamão ≈ mah-MOWN
  The ão is nasal, which English does not really have.

• abacaxi ≈ ah-bah-kah-SHEE
  In Brazilian Portuguese, xi usually sounds like shee.

• difícil ≈ jee-FEE-seew or djee-FEE-seew
  The first di often sounds like djee in many Brazilian accents.

Also:

• stress usually falls on:
  • mamÃO
  • abacaXI
  • diFÍcil

It can describe both, but the meaning changes with context.

For fruit

• maduro = ripe

For people

• maduro = mature

Examples:

• A banana está madura. = The banana is ripe.
• Ele é muito maduro para a idade dele. = He is very mature for his age.

So the same adjective can have different natural translations depending on the noun.

Yes, it is natural and correct.

It sounds like a descriptive sentence about fruit, especially in a context such as cooking, shopping, or checking whether fruit is ready to eat.

A Brazilian speaker might also say similar versions like:

• O mamão e o abacaxi já estavam maduros, mas a pera ainda estava difícil de descascar.
• O mamão e o abacaxi estavam maduros, mas a casca da pera ainda era difícil de remover.

But your original sentence is perfectly good and natural.