O café com açúcar está mais doce do que o outro.

In Portuguese, it is very common to use the definite article with nouns when talking about a specific thing already identified in the situation.

So o café com açúcar means the coffee with sugar.

If you said just café, it could sound more general, like coffee as a substance or category. In this sentence, the speaker is comparing one specific coffee to another one, so o café sounds natural.

Com açúcar means with sugar, and here it describes which coffee we are talking about.

So:

• o café com açúcar = the coffee with sugar

This phrase works like the coffee with sugar in English. It identifies one coffee by adding extra information after the noun.

Portuguese often places these descriptive prepositional phrases directly after the noun they modify.

Portuguese has two verbs for to be: ser and estar.

Here, está is used because sweetness is being treated as a current condition or result, not as an essential characteristic.

• está mais doce = is sweeter / tastes sweeter right now

This makes sense because the coffee’s sweetness can change depending on how much sugar was added.

If you used é, it would sound more like a permanent or defining quality, which is less natural here.

Mais doce is the regular way to form the comparative of sweet in Portuguese.

• doce = sweet
• mais doce = sweeter / more sweet

Portuguese usually forms comparatives with:

• mais + adjective

Examples:

• mais caro = more expensive
• mais frio = colder / more cold
• mais doce = sweeter

Unlike English, Portuguese does not usually add an ending like -er to the adjective.

Do que is a very common way to say than in comparisons.

So:

• mais doce do que o outro = sweeter than the other one

A useful pattern is:

• mais ... do que ... = more ... than ...
• menos ... do que ... = less ... than ...

In everyday Brazilian Portuguese, you may also hear mais doce que o outro without do, and that is also common. But do que is a very standard full form.

Doce is an adjective that has the same form for masculine and feminine in the singular.

So you get:

• o café doce = the sweet coffee
• a bebida doce = the sweet drink

The adjective still agrees in number:

• singular: doce
• plural: doces

Examples:

• os cafés doces
• as bebidas doces

So it does agree, but not every adjective changes for gender in the singular.

Because Portuguese often leaves out a noun when it is already understood from context.

Here, o outro means the other one, with coffee understood.

So these are both possible:

• mais doce do que o outro
• mais doce do que o outro café

The shorter version sounds very natural because repeating café is unnecessary if both speakers already know what is being compared.

In this sentence, o outro means the other one. The article helps turn outro into a noun-like expression.

• o outro = the other one
• a outra = the other one (feminine)
• os outros = the other ones

Without the article, outro usually works more directly as a determiner before a noun:

• outro café = another coffee / another cup of coffee
• a outra xícara = the other cup

So here, o outro is natural because the noun café is omitted.

Yes. In Brazilian Portuguese, both are common:

• mais doce do que o outro
• mais doce que o outro

Both mean the same thing here.
Do que is a bit fuller and often taught as the standard comparative structure, but que alone is very common in real speech.

Yes, and that is exactly what is happening here.

• com açúcar = with sugar

When talking about an ingredient or substance in a general way, Portuguese often uses no article:

• café com leite
• chá com açúcar
• pão com manteiga

If you said com o açúcar, it would usually mean with the sugar in a more specific sense, referring to a particular sugar already identified in context.

The structure is:

• O café com açúcar = subject
• está = verb
• mais doce do que o outro = comparison phrase

So the full pattern is:

• [subject] + está + mais + adjective + do que + comparison

You can reuse this pattern easily:

• O chá está mais quente do que o café.
• Esta fruta está mais madura do que a outra.
• O suco está mais frio do que a água.

It is a very useful pattern for making comparisons in Portuguese.

Yes. In this sentence, doce clearly refers to taste.

• doce = sweet

Since the sentence talks about coffee with sugar, the meaning is specifically about flavor: the coffee tastes sweeter.

Just as a side note, doce can also be a noun in Portuguese meaning a sweet / dessert / candy, depending on context. But here it is definitely an adjective meaning sweet.