Ni vizuri juisi kupozwa kabla ya kunywa.

Because -zuri changes form depending on how it is being used.

• nzuri agrees with a class 9 noun like juisi: juisi nzuri = good juice
• vizuri is the common adverbial/predicative form meaning well, good, or properly

So in Ni vizuri, the phrase is not directly describing juisi. It is making a general judgment: it is good / it is advisable.

It is an impersonal expression.

Swahili often says ni + adjective/adverb where English uses it is .... There is no dummy subject like English it.

So:

• Ni vizuri = It is good
• more naturally in context, It is good that... or It is best to...

It introduces the speaker’s opinion or recommendation.

kupozwa is the infinitive passive form of the verb -poza.

Breakdown:

• -poza = cool/chill something
• kupoza = to cool/chill
• kupozwa = to be cooled/chilled

The -w- is the passive marker, so the juice is receiving the action rather than doing it.

Because the two verbs are different in meaning:

• kupoa = to cool down, to become cool
• kupozwa = to be cooled, to be chilled by someone/something

So:

• Juisi imepoa = The juice has cooled down
• Juisi imepozwa = The juice has been chilled

In this sentence, the idea is that the juice should undergo the chilling action, so the passive kupozwa fits well.

Here, kupozwa is an infinitive that behaves a bit like a noun or verbal noun.

So juisi kupozwa means something like:

• the juice being chilled
• for the juice to be chilled
• the chilling of the juice

After Ni vizuri, Swahili can use this kind of infinitive phrase instead of a full finite clause.

A fuller clause would be something like:

• Ni vizuri juisi ipozwe kabla ya kunywa

That version uses a normal agreeing verb. The original sentence is more compact.

Literally, it means before drinking.

Breakdown:

• kabla = before
• ya = linker used here before a following noun or infinitive phrase
• kunywa = to drink / drinking

This pattern is very common in Swahili:

• kabla ya kula = before eating
• kabla ya kwenda = before going
• kabla ya kulala = before sleeping

So kabla ya kunywa is a normal and useful structure to remember.

Because the object can be left unstated when it is obvious from context.

• kunywa = to drink
• kuinywa = to drink it

The i- in kuinywa is the object marker referring to juisi, which is usually treated as a class 9 noun.

So both ideas are possible:

• kabla ya kunywa = before drinking
• kabla ya kuinywa = before drinking it

In the original sentence, the object is already clear, so Swahili can leave it out.

Because Swahili does not have articles like English a, an, or the.

So juisi can mean:

• juice
• the juice
• some juice

The exact meaning depends on context.

This is very normal in Swahili, and learners often have to get used to relying more on context than on articles.

juisi is a loanword and is commonly treated as a class 9 noun.

That matters when agreement shows up elsewhere. For example:

• Juisi imepozwa = The juice has been chilled
• kuinywa = to drink it, where i- refers to a class 9 object

In this sentence, there is no visible agreement directly attached to juisi, so the noun class is not obvious at first glance. But it becomes important in other sentences.

No. It is understandable, but there are other natural ways to express the same idea.

For example:

• Ni vizuri kupoza juisi kabla ya kunywa = It is good to chill the juice before drinking it
• Ni vizuri juisi ipozwe kabla ya kunywa = It is good that the juice be chilled before drinking

The original Ni vizuri juisi kupozwa kabla ya kunywa is fairly compact and somewhat formal in feel because it uses the passive infinitive kupozwa.