Learn German: Warum ist diese Hälfte so salzig?

In German, most fraction nouns are made by adding -tel to the number (like das Viertel for a fourth or das Drittel for a third). However, "a half" is a major exception. The word "Zweitel" does not exist; instead, you always use the feminine noun die Hälfte.

Could I use the word halb instead of Hälfte in this sentence?

No, because they have different grammatical roles. Hälfte is a noun meaning "the half" of something, which is what we need here as the subject. The word halb is an adjective used to describe another noun, as in ein halbes Glas (a half glass). Since you are talking about "this half" as a thing itself, it must be the noun die Hälfte.

Why does diese end in an -e in this sentence?

The noun Hälfte is feminine (die Hälfte). Because it is the subject of the sentence (in the nominative case), the demonstrative pronoun for "this" takes the feminine nominative ending -e, making it diese.

How is the word salzig formed?