How to remove items from the "Open With" menu in thunar?

[Chris Green]

As per the subject, how do you *remove* entries from the list of
applications that you get to see when you right click on a file in
thunar?

I know how to set the preferred application that the file is opened with
if you activate the file but I can't see how to get rid of entries in
the sub-menu that opens if you click on "Open With".

-- 
Chris Green