Not Westvleteren, Struise.
I miss-typed, not their best beer in the world (The Black Albert only comes in at #4) but their best "Brewer" in the world. My bad, sorry.
You are a better palate than me if you could pick the yeast change in the Hightail out. Its not that I'm saying the beer hasn't changed, been drinking it for years now and it definitely has - it changed when they changed yeasts, it changed when they changed breweries, it changed when they upsized their fermentors, it changes from batch to batch because they (like most other micros) don't have great consistency and most noticeably it changes from venue to venue because of the handling practices of the pub and the length of time and conditions under which it has been stored in bottles.
To be perfectly honest, one of the features of hightail for me is that it is a good base beer that I like the general profile of, but but I am always interested to see what it tastes like "this week". The changeability is much less noticable if you drink it at the brewery though, which is why I mainly point the finger at handling once its been distributed.
If you can pick the particular change that was wrought by the change from a not particularly estery yeast to a "clean" yeast out of that little lot... get you to a competition, they need good judges.
It certainly changed about 8-12 months ago - because for the previous 12 months I couldn't drink the stuff because it was riddled with diacetyl every time I tasted it. If getting rid of that was the result of the yeast change, then I say thank god. But it probably wasn't that. It could have been anything.
I wonder what will change now that they have a brand new head brewer?? I bet its tasteable if you really go looking for it... but I probably wont notice it.