Når jeg har vasket trøjerne, vrider jeg dem forsigtigt, så stoffet ikke bliver ødelagt.

Når means when and is used for something that happens regularly, generally, or in the future.

So Når jeg har vasket trøjerne ... means something like:

• When I have washed the sweaters ...
• more naturally in English here: After washing the sweaters ... / Whenever I’ve washed the sweaters ...

A learner might compare it with:

• da = when for a specific event in the past
• når = when/whenever for repeated situations or something expected to happen

So Når is the natural choice because this sentence describes a general routine.

Har vasket is the present perfect:

• har = have/has
• vasket = past participle of vaske (to wash)

In this sentence, it shows that the washing is completed before the next action happens:

• first: jeg har vasket trøjerne
• then: jeg vrider dem forsigtigt

So the structure emphasizes sequence: once I have washed them, I wring them carefully.

Why not the others?

• vasker = am washing / wash; this would not show the first action as completed in the same clear way
• vaskede = washed; that would sound like a specific past event rather than a general routine

This is because Danish has V2 word order in main clauses. That means the finite verb usually comes in the second position.

The first part of the sentence is a subordinate clause:

• Når jeg har vasket trøjerne

After that, the main clause begins. Since the subordinate clause takes the first position in the sentence, the verb of the main clause must come next:

• Når jeg har vasket trøjerne, vrider jeg dem forsigtigt

So the order is:

1. fronted element: Når jeg har vasket trøjerne
2. finite verb: vrider
3. subject: jeg

This is very common in Danish.

Compare:

• Jeg vrider dem forsigtigt.
• Når jeg har vasket trøjerne, vrider jeg dem forsigtigt.

Vrider is the present tense of vride, which means to wring, to twist, or to squeeze by twisting.

In the context of laundry, vride means to twist wet clothes to get water out.

So:

• jeg vrider dem forsigtigt = I wring them carefully

It is more specific than just squeeze. It suggests a twisting motion.

Dem means them and refers back to trøjerne (the sweaters/shirts/jumpers, depending on context).

So:

• trøjerne = the clothes
• dem = them

Danish uses object pronouns here just like English does:

• Jeg vrider trøjerne = I wring the sweaters
• Jeg vrider dem = I wring them

Because dem is the object of vrider, it is the correct pronoun form.

Trøjerne is the definite plural form of trøje.

Forms:

• en trøje = a sweater / shirt / jersey
• trøjen = the sweater
• trøjer = sweaters
• trøjerne = the sweaters

So the ending -ne marks definite plural.

Danish often adds definiteness as an ending rather than using a separate word like the.

Forsigtigt is the adverb form, meaning carefully.

• forsigtig = careful (adjective)
• forsigtigt = carefully (adverb)

Here it describes how the person wrings the clothes:

• jeg vrider dem forsigtigt = I wring them carefully

This -t ending is very common when an adjective is used adverbially in Danish.

Here så means so that.

It introduces a clause expressing purpose or intended result:

• så stoffet ikke bliver ødelagt
• so that the fabric does not get damaged

This is different from other uses of så, which can also mean:

• so
• then
• such

In this sentence, the meaning is clearly so that.

Because this is a subordinate clause, and Danish word order changes in subordinate clauses.

In a main clause, you often get:

• Stoffet bliver ikke ødelagt.
• The fabric does not get damaged.

But after a subordinating word like så, the negative ikke usually comes before the finite verb:

• så stoffet ikke bliver ødelagt

This is a very important pattern in Danish:

• main clause: verb before ikke
• subordinate clause: ikke before verb

Stoffet means the fabric.

The base noun is:

• stof = fabric/material

Its definite singular form is:

• stoffet = the fabric

The ending -et is a common definite ending for neuter nouns.

So:

• et stof = a fabric / a material
• stoffet = the fabric

Also notice the doubled f in the spelling of the definite form.

Bliver ødelagt means gets damaged or is damaged.

It is a common Danish way of expressing the passive:

• bliver = becomes / gets
• ødelagt = damaged / ruined

So:

• stoffet ikke bliver ødelagt = the fabric does not get damaged

This often sounds more natural in English as get damaged rather than become damaged.

You can think of it as a passive construction:

• active: Noget ødelægger stoffet = Something damages the fabric
• passive: Stoffet bliver ødelagt = The fabric gets damaged

Danish often uses the present tense to describe:

• habits
• routines
• general truths
• instructions

That is what is happening here. The sentence is not necessarily about one specific occasion; it describes what someone typically does:

• Når jeg har vasket trøjerne, vrider jeg dem forsigtigt ...

In natural English, we might also use the present for this:

• When I’ve washed the sweaters, I wring them carefully ...
• or more naturally: After washing the sweaters, I wring them carefully ...

So the tense choice is normal for a routine action.

In bliver ødelagt, ødelagt is the past participle of ødelægge (to damage / ruin), but in this construction it behaves a lot like an adjective in meaning.

So learners often see it as:

• verb-based form: past participle of ødelægge
• function in the sentence: part of a passive expression, gets damaged

This is very common in Danish:

• blive + past participle

Examples:

• bliver lavet = gets made
• bliver åbnet = gets opened
• bliver ødelagt = gets damaged

So the shortest answer is: it is the past participle used in a passive construction.