None of the Trappist breweries lies on the way between Brussels and Ghent. And none of the Trappist breweries is really easily reached by public transport. Most often public transport brings you somewhere more or less nearby and then you still have to do a substantial walk. Be aware that taking a bus in Belgium (outside bigger cities) can be quite challenging if you are not a local. It's a bit weird. Even inside cities, it can be weird.    

I would go for an alternative plan. There are a couple of great places in Ghent to sample Belgian beers, of any kind. If you do want to visit a brewery, there is one [centrally located in Ghent][1]. 

If brewery is the Leitmotiv, the [Cantillon][2] brewery/museum in Brussels is worth a visit too. It is [pretty close to the Midi train station][3]. Cantillon is known for its Kriek, Faro, and Gueuze kind of beers. These are typical local beers from Brussels.   


  [1]: http://www.gruut.be/
  [2]: http://www.cantillon.be
  [3]: http://maps.google.be/maps?saddr=Zuidstation%202/3%[email protected],4.335629&daddr=Brasserie%20Cantillon,%20Gheudestraat,%20Anderlecht&hl=nl&sll=50.838549,4.334407&sspn=0.009269,0.021265&geocode=Fa-2BwMdDShCAA;FfrHBwMdcSZCACFpyOVw0NeNBSkp-uQOc8TDRzFpyOVw0NeNBQ&oq=Cantil&dirflg=w&mra=ls&t=m&z=17