Jo koldere det bliver, jo mere kaffe drikker jeg om morgenen.

It expresses a comparison that corresponds to English the ... the ..., as in:

• The colder it gets, the more coffee I drink in the morning.

So in this sentence:

• Jo koldere det bliver = The colder it gets
• jo mere kaffe drikker jeg om morgenen = the more coffee I drink in the morning

This pattern is very common in Danish for showing that one thing changes together with another.

Koldere is the comparative form of kold (cold), just like colder in English.

• kold = cold
• koldere = colder
• koldest = coldest

For many short adjectives, Danish forms the comparative with -ere rather than using mere.

So:

• koldere = correct
• mere kold = not natural here

By contrast, mere is used with nouns here: mere kaffe = more coffee.

Det bliver literally means it becomes or it gets.

In weather or general-condition statements, Danish often uses det in the same way English uses it:

• Det bliver koldt = It gets cold
• Det bliver varmere = It gets warmer

So Jo koldere det bliver means The colder it gets.

Because kaffe is treated as an uncountable noun here, like coffee in English.

Use:

• mere with uncountable nouns: mere kaffe, mere vand, mere tid
• flere with countable plural nouns: flere kopper, flere bøger, flere mennesker

So:

• mere kaffe = more coffee
• flere kopper kaffe = more cups of coffee

This happens because Danish uses verb-second word order in main clauses.

In the second half of the sentence, the phrase jo mere kaffe comes first. When something other than the subject is placed first, the finite verb usually comes before the subject:

• Jeg drikker mere kaffe om morgenen.
• Jo mere kaffe drikker jeg om morgenen.

So after the fronted element jo mere kaffe, the verb drikker comes before jeg.

This is very normal Danish syntax.

No, not really.

Danish jo can be used in different ways. In this sentence, jo is part of the fixed comparative pattern jo ... jo ....

That is different from the separate word jo used in replies, such as contradicting a negative statement:

• Du kommer ikke.
• Jo, jeg gør.

So although the word looks the same, its function here is different.

Yes, sometimes desto can be used in similar comparative structures, especially in more formal or written Danish. For example:

• Jo koldere det bliver, desto mere kaffe drikker jeg.

That said, jo ... jo ... is very common and natural, and it is the safest pattern for learners to use.

The comma separates the two linked parts of the comparison:

• Jo koldere det bliver
• jo mere kaffe drikker jeg om morgenen

In Danish, this kind of structure is normally written with a comma between the two clauses. It helps show the relationship clearly.

Om morgenen means in the morning.

• om here is used in time expressions
• morgenen is the definite form of morgen (morning)

Compare:

• om morgenen = in the morning
• om aftenen = in the evening
• om natten = at night

So the sentence is specifically talking about the speaker’s coffee drinking in the morning.

Yes, but the meaning shifts slightly.

• Jo koldere det bliver = The colder it gets
  This emphasizes change over time.
• Jo koldere det er = The colder it is
  This focuses more on the temperature as a condition, not the process of becoming colder.

In many situations, both are possible, but bliver fits especially well when you mean that the weather is getting colder.

The normal statement would be:

• Jeg drikker mere kaffe om morgenen.

That means I drink more coffee in the morning.

When you put it into the jo ... jo ... pattern, mere kaffe is moved to the front of the clause:

• jo mere kaffe drikker jeg om morgenen

This fronting triggers the word order change to drikker jeg.

Yes, it sounds natural and idiomatic.

A Danish speaker would readily understand it, and the jo ... jo ... structure is common in both speech and writing. It is a very useful pattern to learn because you can use it with many adjectives and situations:

• Jo ældre jeg bliver, jo mere tålmodig bliver jeg.
• Jo mere jeg læser, jo bedre forstår jeg.
• Jo tidligere du kommer, jo bedre.