Learn Hardcore German: Die Bibliothek bewertet alle Rezensionen erneut, bevor sie online gespeichert werden. - The library rates all reviews again before they are saved online.

In German main clauses the finite (conjugated) verb must occupy the second position. Here Die Bibliothek is the first element, so bewertet comes immediately after it. Everything else follows in positions three, four, etc.

What is the grammatical case of alle Rezensionen, and how can I recognize it?

Alle Rezensionen is in the accusative plural. Clues:
• bewerten is a transitive verb taking a direct object → accusative case.
• Rezensionen is the plural of Rezension. With the determiner alle, the form stays alle Rezensionen in both nominative and accusative plural.

Why is erneut placed after alle Rezensionen rather than directly before bewertet?

German adverb placement usually follows this hierarchy:

Time
Manner (how)
Place
Here erneut (“again”) is an adverb of manner/time and normally follows the object. You could say Die Bibliothek bewertet erneut alle Rezensionen to shift emphasis, but putting erneut after the object is most neutral.

What role does bevor play in bevor sie online gespeichert werden, and why does the verb move to the end?

Bevor is a subordinating conjunction (“before”). In German subordinate clauses introduced by words like bevor, weil, dass, etc., the finite verb goes to the very end. Hence werden follows the past participle gespeichert.

Why is gespeichert werden expressed with two words instead of one?

This is the passive voice. German forms the passive with:
• the past participle of the main verb (gespeichert)
• plus the auxiliary werden in its appropriate tense.
So gespeichert werden = “to be stored.”

Does sie in bevor sie online gespeichert werden refer to die Bibliothek or Rezensionen?

It refers to Rezensionen. Although die Bibliothek is feminine singular, Rezensionen is plural. Here sie is the accusative plural pronoun replacing alle Rezensionen.

How would I rewrite the sentence in active voice instead of passive?

You can make die Bibliothek the subject of both verbs:
“Die Bibliothek bewertet alle Rezensionen erneut, bevor sie die Rezensionen online speichert.”
Or more naturally:
“Die Bibliothek bewertet alle Rezensionen erneut, bevor sie sie online speichert.”

Can I replace erneut with noch einmal, and if so, does the word order change?

Yes. Erneut and noch einmal are synonyms for “again.” You can say either:
“Die Bibliothek bewertet alle Rezensionen erneut …”
“Die Bibliothek bewertet alle Rezensionen noch einmal …”
Word order stays the same, since noch einmal also functions as an adverbial phrase.

Is it acceptable to move online elsewhere in the subordinate clause, for example bevor sie gespeichert online werden?

No. Adverbs like online typically precede the past participle in a passive subordinate clause:
“bevor sie online gespeichert werden.”
Swapping places (“gespeichert online”) would sound awkward and isn’t standard word order in German.