De or het vermouting?

The correct Dutch article is:

de vermouting

Rule Words ending in -ing: almost always de. See the rule

How to use vermouting

the vermoutingde vermouting
this vermoutingdeze vermouting
that vermoutingdie vermouting
our vermoutingonze vermouting
your vermoutingjouw vermouting
every vermoutingelke vermouting
which vermouting?welke vermouting?
a big vermouting / the big vermoutingeen grote vermouting, de grote vermouting