Colons may be used to separate independent clauses that are not separated by a conjunction or any other connecting word or phrase.
Semicolons are normally used, but the colon adds emphasis, especially if the first clause leads into the second clause or has a parallel construction.
The second clause begins with a capital letter.
Correct: Grapes are not squeezed: The pulp is pressed.
Some authorities do not capitalize the word following the colon when the subject or point of view does not change between the first and second clauses.