Die kos bederf.

Here, die means the.

Afrikaans does not have grammatical gender the way German or Dutch does, so you do not need different definite articles for masculine, feminine, or neuter nouns. Die is the normal definite article for nouns in general.

A useful contrast:

• die kos = the food
• 'n kos would not normally be used here, because kos is usually treated like food in English rather than a food

Because bederf is already a full verb.

This sentence is not built like The food is bad. It is built like The food spoils / goes bad / is spoiling.

So:

• Die kos bederf = the food spoils / is spoiling / goes bad
• Die kos is bedorwe = the food is spoiled

In other words, bederf expresses the action or process, so no extra is is needed.

It is the present tense.

In Afrikaans, the present tense often covers both:

• a general statement: Food spoils
• something happening now: The food is spoiling

So Die kos bederf can mean:

• The food spoils
• The food is spoiling
• The food goes bad

The exact English translation depends on context.

No. Afrikaans verbs usually do not change form for different subjects in the present tense.

So the verb stays bederf:

• Die kos bederf
• Die vrugte bederf
• Ek bederf dit
• Hulle bederf dit

This is much simpler than English, where you have forms like I spoil but it spoils.

No. Bederf has a wider meaning than just food.

It can mean:

• to spoil / go bad for food
• to ruin
• to spoil in the sense of overindulging someone

Examples:

• Die kos bederf. = The food goes bad.
• Die hitte bederf die kos. = The heat spoils the food.
• Sy bederf haar kinders. = She spoils her children.

In your sentence, bederf is being used in the food-related sense.

In Die kos bederf, it is intransitive.

That means the subject itself is undergoing the action:

• the food is what is going bad

But bederf can also be transitive, where something spoils something else:

• Die hitte bederf die kos. = The heat spoils the food.

So the same verb can work in both ways, depending on the sentence.

They are related, but not identical.

• Die kos bederf focuses on the process: the food is spoiling / goes bad.
• Die kos is bedorwe focuses on the result/state: the food is spoiled.

So a simple way to think about it is:

• bederf = to spoil / to go bad
• bedorwe = spoiled

The negative is:

Die kos bederf nie.

Afrikaans uses nie for negation. In a short sentence like this, nie can simply come at the end.

If extra words come after the first nie, you normally get another nie at the end:

• Die kos bederf nie vinnig nie. = The food does not spoil quickly.

So this sentence is also a good introduction to how Afrikaans negation works.

Yes. This is normal main-clause word order:

• Die kos = subject
• bederf = verb

So the sentence is simply subject + verb.

If you put another element first, Afrikaans still keeps the verb in second position:

• In warm weer bederf die kos vinnig. = In warm weather, the food spoils quickly.

That means Die kos bederf is a very basic, standard sentence pattern.

A rough pronunciation guide is:

• Die ≈ dee
• kos ≈ koss
• bederf ≈ buh-DERF

The stress is on the second syllable of bederf.

So very roughly:

• dee koss buh-DERF

That is only an approximation, but it is a good starting point for an English speaker.