Learn Hardcore Dutch: Tom zet de waterkoker aan, terwijl Anna het koffiezetapparaat schoonmaakt. - Tom turns the kettle on, while Anna cleans the coffee machine.

Main clause: verb in second place, prefix at the end
- Anna maakt het koffiezetapparaat schoon.
Subordinate clause (introduced by words like terwijl, dat, omdat):
The conjugated verb goes to the end, and the prefix sticks back on:
- … terwijl Anna het koffiezetapparaat schoonmaakt.

So here:

zet … aan appears in a main clause → split.
schoonmaakt appears in a subordinate clause after terwijl → joined.

What exactly does terwijl mean here, and how is it different from tijdens, als, or wanneer?

Terwijl means while / at the same time as and introduces a subordinate clause with its own subject and verb.

Tom zet de waterkoker aan, terwijl Anna het koffiezetapparaat schoonmaakt.
→ Two full actions happening simultaneously.

Differences:

tijdens = during, but is a preposition, not a conjunction:
- Tijdens het schoonmaken zet Tom de waterkoker aan.
  (het schoonmaken is a noun phrase, not a full clause.)
als / wanneer often mean when (general or conditional, not necessarily at exactly the same time):
- Als Anna het koffiezetapparaat schoonmaakt, zet Tom de waterkoker aan.
  → more like “whenever / if Anna cleans, Tom turns on the kettle.”

So in this sentence, terwijl is best because you want two simultaneous ongoing actions with full clauses.

Why does the verb move to the end after terwijl?

Terwijl starts a subordinate clause. In Dutch subordinate clauses, the conjugated verb usually comes at the end of the clause.

Patterns:

Main clause:
Anna maakt het koffiezetapparaat schoon.
(Verb 2nd position)
Subordinate clause:
… terwijl Anna het koffiezetapparaat schoonmaakt.
(schoonmaakt goes to the end, and schoon reattaches.)

The sentence you gave has:

Main clause: Tom zet de waterkoker aan
Subordinate clause: terwijl Anna het koffiezetapparaat schoonmaakt

Why is it de waterkoker but het koffiezetapparaat?

Dutch has two definite articles:

de for common-gender nouns
het for neuter nouns

In this case:

de waterkoker → waterkoker is common gender.
het koffiezetapparaat → koffiezetapparaat is neuter.

Unfortunately, gender is often arbitrary and must be memorized with the noun. There are patterns, but waterkoker and koffiezetapparaat don’t follow a simple one that learners can reliably guess from.

So learn them as:

de waterkoker
het koffiezetapparaat

What does the long compound word koffiezetapparaat literally mean?

Dutch loves compound nouns written as one word.

koffiezetapparaat breaks down as:

koffie = coffee
zet(ten) = to brew / to make (coffee, tea, etc.)
apparaat = machine / device

So koffiezetapparaat is literally a “coffee-brewing device”, i.e. a coffee maker / coffee machine.

Spelling: it’s written as one word, not koffie zet apparaat or koffie-zet-apparaat.

Why is Dutch using the simple present (zet, schoonmaakt) if the actions are happening right now?

In Dutch, the simple present is used much more broadly than in English. It is perfectly normal for actions happening right now.

So:

Tom zet de waterkoker aan.
= “Tom is turning on the kettle.”
Anna maakt het koffiezetapparaat schoon.
= “Anna is cleaning the coffee machine.”

There is a progressive form (is aan het schoonmaken, zit te schoonmaken), but it’s not needed here and would sound heavier. The simple present already naturally covers the English present continuous in many everyday contexts.

Is there a more “progressive” way to say that Anna is cleaning?

Yes. Dutch has ways to emphasize an ongoing action, though they’re not always necessary.

Possible variants:

Terwijl Anna het koffiezetapparaat aan het schoonmaken is.
→ very explicitly “while Anna is in the process of cleaning the coffee machine.”
Terwijl Anna zit te schoonmaken.
→ literally “while Anna sits cleaning” (only if she’s actually sitting).

In normal speech, terwijl Anna het koffiezetapparaat schoonmaakt is already perfectly natural to express “while Anna is cleaning the coffee machine.”

Is the comma before terwijl required?

In this sentence, the comma is standard and recommended, but you will sometimes see it omitted in informal writing.

General rule:

Put a comma before a subordinate clause that follows the main clause:
- Tom zet de waterkoker aan, terwijl Anna het koffiezetapparaat schoonmaakt.

If you reverse the order and start with the subordinate clause, you must use a comma at the end of that clause:

Terwijl Anna het koffiezetapparaat schoonmaakt, zet Tom de waterkoker aan.

Can I swap the two clauses and say Terwijl Anna …, zet Tom …?

Yes. Both orders are correct:

Tom zet de waterkoker aan, terwijl Anna het koffiezetapparaat schoonmaakt.
Terwijl Anna het koffiezetapparaat schoonmaakt, zet Tom de waterkoker aan.

Meaning and grammar stay the same:

The clause with terwijl is still subordinate (verb at the end).
The main clause still has the verb in second position (zet).

Could I say Tom doet de waterkoker aan or Tom zet de waterkoker op instead of zet de waterkoker aan?

Native usage here strongly prefers aanzetten with waterkoker:

Tom zet de waterkoker aan. ✅ natural
Tom doet de waterkoker aan. ⚠️ understandable, but uncommon / awkward
Tom zet de waterkoker op. ⚠️ could be interpreted as “puts the kettle on (a stove)” rather than “switches it on,” and is less standard for an electric kettle.

For an electric kettle, the idiomatic verb is:

de waterkoker aanzetten = to turn/switch the kettle on.

For a stovetop kettle, people might say:

de ketel op het vuur zetten = to put the kettle on the fire/stove.

How do you pronounce koffiezetapparaat, and where is the stress?

Pronunciation (approximate for English speakers):

koffiezetapparaat: KOF-fie-zet-ap-pa-RAAT

More precisely (IPA): /ˈkɔ.fi.zɛt.ɑ.paˌraːt/
Stress pattern:

main stress on kof (first syllable)
secondary stress on raat (last syllable)

Each part keeps its “own” sound:

koffie → KOF-fie
zet → zet
apparaat → ap-pa-RAAT

And because it’s Dutch, the whole thing is written as one long compound word.