Kaffen er altfor varm.

Because -en is the definite article attached to the noun.
The base noun is kaffe = coffee, and kaffen = the coffee.

This is very common in Norwegian:

• en kaffe = a coffee
• kaffen = the coffee

So instead of a separate word like English the, Norwegian often adds the definite ending to the noun.

Er is the present tense of å være = to be.

So:

• kaffen = the coffee
• er = is
• altfor varm = much too hot / far too hot

In a normal Norwegian main clause, the verb usually comes in the second position. That is why er comes right after the subject here.

Altfor means far too, much too, or way too.

So:

• for varm = too hot
• altfor varm = much too hot / far too hot

It makes the idea stronger.
Also, altfor is written as one word.

Yes. Kaffen er for varm is completely correct.

The difference is mainly strength:

• Kaffen er for varm = The coffee is too hot
• Kaffen er altfor varm = The coffee is much too hot / far too hot

So altfor adds extra emphasis.

Because the subject kaffen is a singular common-gender noun, and predicative adjectives agree with the noun.

Here are the basic patterns:

• Kaffen er varm = common gender singular
• Huset er varmt = neuter singular
• Drikkene er varme = plural

Since kaffe is a common-gender noun (en kaffe), the adjective stays varm.

Yes. In Norwegian, varm often covers both warm and hot, depending on context.

With coffee, varm can naturally mean hot.
So Kaffen er altfor varm is exactly what you would say if the coffee is too hot to drink.

It normally refers to a specific coffee, because kaffen is definite: the coffee.

So it usually means something like:

• the coffee on the table
• the coffee I just got
• the coffee we are drinking

If you wanted a more general idea, you would usually not use kaffen in the same way.

A simple learner-friendly pronunciation is roughly:

KAHF-fen

A few useful points:

• the a is short
• the double ff helps show that the vowel before it is short
• the ending -en is the definite ending

So try something like KAHF-fen, not kaa-fen.

Yes, but the verb still stays in second position in a main clause.

For example:

• Kaffen er altfor varm.
• I dag er kaffen altfor varm. = Today, the coffee is much too hot.

Notice that when I dag comes first, er still stays in the second position. This is a very important Norwegian word-order rule.

The dictionary forms are:

• kaffe = coffee
• å være = to be
• altfor = far too / much too
• varm = warm / hot

So kaffen er altfor varm is built from very basic, high-frequency words.