Die Grapefruit schmeckt bitter, aber auch frisch.

Because Grapefruit is a feminine noun in German, so it takes the article die in the nominative singular.

• die Grapefruit = the grapefruit

German nouns have grammatical gender, and you usually have to learn the gender together with the noun.

Because this is a normal German main clause, and in German main clauses the finite verb usually goes in second position.

So the structure is:

• Die Grapefruit = subject
• schmeckt = verb
• bitter = adjective/complement

German word order here is very similar to English:

• The grapefruit tastes bitter.

Here, schmecken means to taste in the sense of having a certain taste.

So:

• Die Grapefruit schmeckt bitter. = The grapefruit tastes bitter.

Be careful: schmecken is not usually used to mean to taste something with your tongue as an action. In this sentence, it describes the flavor of the grapefruit.

Because the subject is die Grapefruit, which is third person singular.

The verb schmecken is conjugated like this in the present tense:

• ich schmecke
• du schmeckst
• er/sie/es schmeckt
• wir schmecken
• ihr schmeckt
• sie/Sie schmecken

Since die Grapefruit = she/it grammatically, you use schmeckt.

Good question. In this sentence, bitter and frisch are predicative adjectives, not adjectives placed directly before a noun.

After verbs like:

• sein = to be
• werden = to become
• bleiben = to remain
• schmecken = to taste

the adjective usually does not take an ending.

So:

• Die Grapefruit ist bitter.
• Die Grapefruit schmeckt bitter.
• Die Grapefruit ist frisch.

But if the adjective comes before a noun, then it does take an ending:

• die bittere Grapefruit
• die frische Grapefruit

Aber auch means something like but also.

So the sentence says that the grapefruit has two qualities at the same time:

• it tastes bitter
• but also fresh

This combination is very natural in German. It adds a contrast, but not a contradiction:

• bitter, aber auch frisch = bitter, but also fresh

Because aber is a coordinating conjunction, and in German it is normally preceded by a comma when it connects two parts of a sentence like this.

So:

• Die Grapefruit schmeckt bitter, aber auch frisch.

This is standard punctuation in German.

Yes, but the meaning is slightly different.

• Die Grapefruit ist bitter. = The grapefruit is bitter.
• Die Grapefruit schmeckt bitter. = The grapefruit tastes bitter.

With food, schmecken is often more natural when you are talking specifically about flavor. Sein is possible too, but schmecken focuses more directly on taste.

Yes, frisch can describe taste too. In food contexts, it often means something like:

• fresh-tasting
• lively
• refreshing

So in this sentence, frisch does not just mean recently picked. It describes the impression of the flavor.

Yes, but the verb still has to stay in second position in a main clause.

For example, you could say:

• Bitter, aber auch frisch schmeckt die Grapefruit.

This sounds more stylistic or emphatic, because it emphasizes the taste description first.

The neutral, most natural order is still:

• Die Grapefruit schmeckt bitter, aber auch frisch.

Yes, it sounds natural. It is a normal way to describe flavor.

A speaker might use it when talking about fruit, juice, or food in general. The sentence feels descriptive and idiomatic.

If someone wanted to sound a little more conversational, they might also say:

• Die Grapefruit schmeckt bitter, aber irgendwie auch frisch.
• Die Grapefruit ist bitter, aber auch sehr erfrischend.

But your original sentence is perfectly correct and natural.