Ryst flasken forsigtigt, før du hælder juicen op.

Ryst is the imperative form of at ryste (to shake).

Danish uses the imperative for commands, instructions, and recipe-style directions:

• Ryst flasken = Shake the bottle
• Åbn døren = Open the door
• Vent lidt = Wait a moment

Like English, Danish usually does not include the subject in an imperative, so Ryst by itself already means Shake (you).

Because flasken means the bottle, while en flaske means a bottle.

Danish often makes nouns definite by adding the article to the end of the noun:

• en flaske = a bottle
• flasken = the bottle

In this sentence, the speaker means a specific bottle — the one with the juice in it — so flasken is the natural choice.

For the same reason: juicen means the juice.

• en juice = a juice / a juice drink
• juicen = the juice

Here it refers to a specific juice already known from the situation, so the definite form is used.

Also, juice is a loanword in Danish, but it still follows normal Danish grammar.

Because forsigtigt is the form used adverbially here, meaning carefully / gently.

• forsigtig = careful as an adjective
• forsigtigt = carefully as an adverb-like form

Examples:

• en forsigtig mand = a careful man
• Hun kører forsigtigt = She drives carefully
• Ryst flasken forsigtigt = Shake the bottle gently/carefully

A useful pattern is that Danish often uses the -t form when an adjective describes how an action is done.

Før means before.

In this sentence, it introduces the action that should happen later:

• Ryst flasken forsigtigt, før du hælder juicen op.
• Shake the bottle gently before you pour the juice.

So the order is:

1. shake the bottle
2. then pour the juice

Here, før is a conjunction introducing a subordinate clause.

Often, yes. Inden can also mean before.

For example:

• før du hælder juicen op
• inden du hælder juicen op

Both can work in many situations. In everyday Danish, før is very common and natural here.

A rough way to think about it:

• før = before
• inden = before / before the point when

In this sentence, før is completely standard.

Because after før, you are in a subordinate clause, and Danish word order changes.

In a main clause, Danish normally has verb-second word order:

• Nu hælder du juicen op. = Now you pour the juice.

But after a subordinating word like før, the subject usually comes before the finite verb:

• før du hælder juicen op

So:

• du hælder = correct here
• hælder du = not correct in this clause

This is a very important Danish pattern:

• main clause: often verb in second position
• subordinate clause: subject before verb

Because Danish uses a normal finite verb form after før, even when the action is still in the future relative to the command.

So:

• før du hælder juicen op literally uses present tense
• but the meaning is still before you pour the juice

English does something similar:

• Shake the bottle before you pour the juice

You do not need a future form here in Danish.

Hælde op is a common Danish verb combination meaning to pour out / pour into glasses or cups / serve by pouring.

So:

• at hælde = to pour, to tilt
• at hælde op = to pour out / serve by pouring

In this sentence, hælder juicen op means something like:

• pour the juice
• pour out the juice
• serve the juice by pouring it

The small word op does not always have to be translated literally as up. In Danish, it often helps create the natural meaning of the whole verb expression.

Because hælde op behaves a bit like a phrasal verb, and when there is an object, Danish often places the object before the particle:

• du hælder juicen op
• hun skriver nummeret ned
• vi tager jakken af

So the pattern is often:

verb + object + particle

Here:

• hælder = verb
• juicen = object
• op = particle

That is why you get hælder juicen op, not hælder op juicen.

Not in this sentence.

After før, Danish normally wants a clause such as:

• før du hælder juicen op = before you pour the juice

If you said Hæld juicen op, that would be a new command:

• Ryst flasken forsigtigt. Hæld juicen op.
• Shake the bottle gently. Pour the juice.

So the original sentence has:

• one main command: Ryst
• one subordinate clause: før du hælder juicen op

The comma is correct, but whether it is strictly required depends on the comma system being used.

In Danish, many writers place a comma before a subordinate clause like this:

• Ryst flasken forsigtigt, før du hælder juicen op.

That is very normal and fully correct.

You may also sometimes see Danish written without that comma, depending on style and comma conventions. But the version with the comma is completely standard and very common, especially in clear instructional writing.