Uncountable nouns can be specified or measured.
You can add a measure word (unit of measurement) --> This specifies the quantity of the noun.
e.g.
coffee = uncountable noun. (koffie)
measure word: cup (kopje)
--> a cup of coffee = een kopje koffie
a cup of coffee is countable ! one cup of coffee, two cups of coffee,....
Uncountable nouns are used with a singular verb and usually don't have a plural form.
To make uncountable nouns countable, we use: quantifiers (e.g. some) and container (a corton).