Çorba kaynadı mı altını kıs; yoksa taşabilir.

Not really. In this sentence, kaynadı mı does not function like a normal question such as Boiled yet?

Here it means something like:

• when it boils
• once it has boiled
• as soon as it boils

So Çorba kaynadı mı altını kıs means Once the soup boils, turn down the heat.

This is a very common Turkish pattern:

• X oldu mu, Y yap.
  = When/once X happens, do Y.

For example:

• Eve vardın mı beni ara.
  = When you arrive home, call me.

This is a common point of confusion for English speakers.

Kaynadı is the definite past form of kaynamak (to boil). But in the pattern verb + -dı mı, Turkish often uses the past form to mean when/once something has happened.

So the logic is not really simple past in the English sense. It is more like:

• after it has boiled
• once it is boiled / once boiling has happened

That is why Turkish says:

• kaynadı mı
  literally: did it boil?
• but functionally here: once it boils / when it has boiled

Because mı/mi/mu/mü is the Turkish question particle, and it is normally written as a separate word.

So:

• kaynadı mı = correct
• kaynadımı = incorrect

Even though it is written separately, it is tightly connected to the word before it in meaning and pronunciation.

Its vowel changes by vowel harmony:

• mı
• mi
• mu
• mü

Here it is mı because of vowel harmony with kaynadı.

Literally, altını kıs is something like lower its underneath or reduce its bottom.

But idiomatically it means:

• turn down the heat under it
• lower the flame
• reduce the heat

In cooking Turkish, this is a very natural expression. You are not really talking about the soup’s physical bottom in a literal way. You are referring to the heat source underneath the pot.

So:

• altını kısmak = to turn down the heat
• altını açmak = to turn up the heat / switch on the heat more

Altını contains extra grammar:

• alt = bottom, lower part
• altı = its bottom / the bottom of it
• altını = its bottom (as a definite object)

In altını kıs, the word is the object of the verb kısmak (to reduce, turn down), so it takes the accusative.

You can think of it roughly like this:

• çorbanın altı = the soup’s underside / what is under the soup
• çorbanın altını kıs = reduce the heat under the soup

In practice, this is a fixed cooking expression, so learners usually just memorize altını kısmak as a chunk meaning turn down the heat.

Kıs is the informal singular imperative of kısmak (to reduce, to turn down).

So it means:

• reduce it
• turn it down

This is the form used when giving a direct instruction to one person:

• Kıs. = Turn it down.

Other related forms:

• kısın = plural/formal imperative
• kısma = don’t turn it down
• kısıyor = is turning down
• kıstı = turned down

In recipes and everyday spoken instructions, the bare imperative like kıs is very common.

Here yoksa means:

• otherwise
• or else
• if not

So:

• Yoksa taşabilir.
  = Otherwise, it may boil over.

Be aware that yoksa can also appear in real-choice questions in other contexts, but here it clearly has the meaning otherwise.

Taşabilir comes from:

• taşmak = to overflow, spill over, boil over
• -abil- = can / may / be able to
• -ir = aorist/general tense marker

So taşabilir means:

• it may boil over
• it can overflow

In this sentence, because the topic is soup, the natural translation is it may boil over.

Because Turkish often leaves out subjects when they are already clear from context.

Here, the subject is understood to be çorba (the soup).

So Turkish does not need to repeat it:

• Çorba kaynadı mı altını kıs; yoksa taşabilir.

The second clause could be expanded for clarity, but it would sound less natural:

• ... yoksa çorba taşabilir.

That is grammatical, but usually unnecessary.

Yes, very natural.

It is a compact, everyday way to give a cooking instruction:

• first: when this happens
• then: do this
• finally: otherwise this may happen

Pattern:

• X oldu mu, Y yap; yoksa Z olur/olabilir.

So this sentence sounds like normal spoken or written practical Turkish, especially in cooking.

Yes. A few natural alternatives are:

• Çorba kaynayınca altını kıs; yoksa taşabilir.
  = When the soup boils, turn down the heat; otherwise it may boil over.

• Çorba kaynadığında altını kıs.
  = Turn down the heat when the soup has boiled.

• Çorba kaynayınca altını kısmazsan taşabilir.
  = If you don’t turn down the heat when the soup boils, it may boil over.

Your original sentence is shorter and very idiomatic.

Both can mean when it boils / once it has boiled, but the nuance is slightly different.

• kaynadı mı often feels a bit like once that happens
• kaynayınca is a straightforward when/when it boils

In many everyday situations, they are very close in meaning.

So:

• Çorba kaynadı mı altını kıs.
• Çorba kaynayınca altını kıs.

Both are natural. The first one can sound especially conversational and instruction-like.

The semicolon separates two closely connected parts:

1. Çorba kaynadı mı altını kıs
2. yoksa taşabilir

It works like a strong pause, stronger than a comma but not as separate as a full stop.

You could also see this written with a comma in informal writing:

• Çorba kaynadı mı altını kıs, yoksa taşabilir.

Or even as two sentences:

• Çorba kaynadı mı altını kıs. Yoksa taşabilir.

The semicolon is just a neat way to show the connection clearly.