Pakastin on jo puolillaan, koska puolisoni teki isoja annoksia valmiiksi.

puolillaan literally means “half-full” or “halfway (filled).”

• It’s formed from puoli (“half”) plus the suffix -llaan, which turns it into an adverb expressing a container’s fill-level.
• You use puolillaan to say that something (here, the freezer) is half full.
• puolessa (the inessive case of puoli) means “in the middle of” or “halfway through” (e.g. elokuvan puolessa = “halfway through the movie”), but it doesn’t convey “half full” for containers.

jo means “already.”

• In Pakastin on jo puolillaan, jo signals that the freezer reached half-capacity sooner than expected.
• Without jo, you’d simply state a fact (“the freezer is half-full”); with jo, you emphasize surprise or that something happened earlier.

puolisoni means “my spouse.”

• The base word puoliso means “spouse” (gender-neutral).
• Adding the possessive suffix -ni (“my”) gives puolisoni = “my spouse.”

annoksia is the partitive plural of annos (“portion” or “batch”). The partitive is used because:

1. You’re talking about an indefinite quantity (“large batches”) rather than a single, countable item.
2. In Finnish, when the object of tehdä (“to make/do”) refers to an unspecified amount, the partitive is required.

valmiiksi is an adverbial form of valmis (“ready”), used in a resultative construction with tehdä.

• tehdä valmiiksi = “to make (something) ready.”
• Here, teki isoja annoksia valmiiksi means “(my spouse) prepared large batches in advance,” emphasizing that the batches were finished and ready to use.

In Finnish, subordinate clauses introduced by conjunctions like koska (“because”) use verb-final word order.

• Main clause: Pakastin on jo puolillaan (Subject-Verb-Adverb-Predicate).
• Subordinate clause: koska puolisoni teki isoja annoksia valmiiksi (Conjunction-Subject-Object-Verb).

Yes, all three can mean “because,” but:

• koska is neutral and very common in both speech and writing.
• siksi että is slightly more formal or explicit (“for the reason that…”).
• sillä is colloquial and often used in spoken Finnish.
  Example:
  “Sillä puolisoni teki isoja annoksia valmiiksi, pakastin on jo puolillaan.” (more informal)
  “Siksi että puolisoni teki isoja annoksia valmiiksi, pakastin on jo puolillaan.” (more formal)