Al salir, mi tía dijo que el vino estaba bueno, pero que la cerveza del otro puesto estaba más fría.

Al + infinitive is a very common Spanish structure meaning when doing, upon doing, or as someone does something.

So al salir means something like:

• when leaving
• as we were leaving
• on the way out

It is formed like this:

• a + el = al
• al + infinitive

Examples:

• Al entrar, saludó a todos. = When he came in / On entering, he greeted everyone.
• Al llegar, vimos a Marta. = When we arrived, we saw Marta.

In your sentence, al salir sets the scene for what happened at that moment.

Not necessarily. One important thing about al + infinitive is that it does not explicitly state the subject.

So al salir could mean:

• as we were leaving
• as she was leaving
• as they were leaving

The subject is understood from the context, not from the grammar of salir itself.

In this sentence, many learners would naturally understand it as something like as we were leaving or on the way out, but the Spanish does not force one exact subject.

This is a classic preterite vs imperfect contrast.

• dijo is preterite from decir
• estaba is imperfect from estar

Why?

dijo

This refers to a completed action: your aunt said something at a specific moment.

estaba

This describes a state or condition at that time: the wine was good, the beer was colder.

So Spanish is treating the sentence like this:

• the act of speaking = a finished event → dijo
• the quality/condition of the drinks = background description → estaba

That is why the combination sounds natural.

Because both parts depend on dijo.

Structure:

• mi tía dijo que el vino estaba bueno
• pero que la cerveza del otro puesto estaba más fría

That second que helps show that the second clause is still part of what your aunt said.

In English, we often would not repeat that:

• My aunt said that the wine was good, but the beer from the other stall was colder.

In Spanish, repeating que is very normal and often sounds clearer and more natural in longer sentences.

You may also hear people omit it in some contexts, but here the repeated que is perfectly standard.

With food and drink, estar bueno usually means to taste good or to be nice/good.

So:

• El vino estaba bueno = The wine tasted good / was good

If you said era bueno, it would sound more like:

• it was a good wine in general
• it was good by nature or quality
• it belonged to the category of good wines

That is a more general or inherent description.

For food and drinks, Spanish very often uses estar bueno for the speaker’s experience of it at that moment.

Examples:

• La tortilla está muy buena. = The omelette tastes really good.
• El café estaba bueno. = The coffee was good.

Here puesto means a stall, stand, or booth, especially at a market, fair, festival, or similar place.

So:

• la cerveza del otro puesto = the beer from the other stall/stand

This is very common in Spain when talking about food or drink being sold in temporary or semi-temporary places.

Because de + el normally contracts to del.

So:

• de + el = del

That gives:

• la cerveza del otro puesto

This is just like:

• a + el = al

Examples:

• Vengo del mercado. = I’m coming from the market.
• Voy al centro. = I’m going to the centre.

The main exception is when El is part of a proper name:

• de El Escorial
  not del Escorial

But in your sentence, el otro puesto is not a proper name, so del is required.

Feminine agreement

Fría agrees with la cerveza, which is feminine singular.

So:

• el vino estaba bueno
• la cerveza estaba más fría

Adjectives in Spanish usually agree in gender and number with the noun.

Comparative

más fría means colder.

Spanish forms the comparative with:

• más + adjective

So:

• fría = cold
• más fría = colder

Accent mark

The accent in fría is there because the i and a are pronounced in separate syllables:

• frí-a

Without the accent, the pronunciation rules would suggest a different sound pattern.

For the same reason as estaba bueno: the sentence is describing the condition of the drink at that moment.

• estaba más fría = it was colder
• this is about how cold it was when they tried it or talked about it

Using ser here would sound unnatural in this context. Temperature, taste, and similar physical states are usually expressed with estar.

Examples:

• La sopa está caliente. = The soup is hot.
• La cerveza estaba fría. = The beer was cold.

Because decir que normally introduces a statement of fact or reported information, so the indicative is used.

Here your aunt said:

• the wine was good
• the beer was colder

So Spanish uses the indicative:

• estaba
• estaba

This is normal after decir que when you are simply reporting what someone said.

You are more likely to see the subjunctive in different kinds of contexts, such as:

• denial
• doubt
• uncertainty
• influence or command

For example:

• No dijo que el vino estuviera bueno.
  = She didn’t say the wine was good.

But in your sentence, it is straightforward reported speech, so indicative is exactly what you would expect.

Yes, Spanish sometimes allows ellipsis, but in this sentence repeating estaba sounds more complete and natural:

• ...pero que la cerveza del otro puesto estaba más fría

If you removed it, the sentence would become less clear and less balanced.

The full version clearly compares two ideas your aunt expressed:

• the wine was good
• the beer from the other stall was colder

So repeating estaba helps the sentence flow properly and keeps the comparison easy to follow.