По мере того как вафли остывали, сироп становился гуще.

to become

Breakdown of По мере того как вафли остывали, сироп становился гуще.

• остывать: to cool down
• вафля: the waffle
• сироп: the syrup

Questions & Answers about По мере того как вафли остывали, сироп становился гуще.

What does по мере того как mean, and when is it used?

По мере того как means as, while, or more literally in proportion as. It is used when two processes develop gradually together.

In this sentence:

• По мере того как вафли остывали... = As the waffles were cooling...
• ...сироп становился гуще = ...the syrup was becoming thicker

So the idea is not just that one thing happened during another, but that the change in one thing went along with the change in the other.

It is a common pattern for gradual change:

• По мере того как темнело, становилось холоднее. = As it got darker, it got colder.

Why is there a comma after остывали?

Because по мере того как вафли остывали is a subordinate clause, and Russian normally separates subordinate clauses from the main clause with a comma.

So the structure is:

• По мере того как вафли остывали, = subordinate clause
• сироп становился гуще. = main clause

This is very similar to English:

• As the waffles cooled, the syrup became thicker.

Why is остывали plural?