Originally Posted by dagamore
one thing to keep in mind is that a lot of the Belgium beers carb with a different yeast then the fermentation one, often they filter out the "good" 'fermentation' yeast so that other brewers can not get that strain/mix of strains from them.
This is one of those things that gets repeated a lot, but I'm really not sure how often it actually happens. Some Belgians do use another yeast for bottling, but most don't actually try to hide their fermentation yeast--usually there's a difference if the main yeast was a different strain than the major house yeast for the brewery. There may be an oddball brewery here and there that actively tries to hide their yeast, but it's not common.
And most of them (the ones that have one main house yeast) just use the house yeast for bottle conditioning.
Off the top of my head for the 7 Trappist breweries:
Rochefort: Bottles with the house yeast, you can culture it fine
Westleveran: Not sure, but they are public about using Westmalle's yeast (they pick it up fresh every brew day) so if they do use another yeast it's not to hide the yeast strain
Achel: Same as Westleveran
Orval: Adds bugs and possibly a secondary yeast strain, if you culture at home you get a mix of everything but the primary strain isn't hidden out.
de Koeningshaven: Not sure
On deck: Little Bo Pils, Bretta Off Dead (Brett pale)
Secondary: Oude Bruin, Red Sky at Morning (Sour brown ale)
On tap: Saison Duphunk (sour), Amarillo Slim (IPA), Earl White (ginger/bergamot wit)
Bottled: Number 8 (Belgian Strong Dark Ale), Eternale (Barleywine), Ancho Villa (Ancho/pasilla/chocolate/cinnamon RIS), Oak smoked porter (1/2 maple bourbon oaked, 1/2 apple brandy oaked)