I know this has been addressed before, although maybe not this exact iteration of the question. I cracked open my very first bottle of Cantillon last night (I've gotten a pour or two at a bar before, but this was the first of my very own bottles); it was a 375 of Rose de Gambrinus. I took off the cap and there was definitely a tiny bit of liquid escaping around the cork just after I removed the cap. I popped the cork, which appeared to be in pretty good shape. The pour looked amazing - pink with a rather large head - and the smell was divine. But when I took the first sip... meh...? It didn't taste half as good as it smelled. It was fine, but to me it wasn't much different than the New Glarus Raspberry tart, which isn't particularly tart. There just wasn't the oomph of flavor that I expected based on previous Cantillon drinks I've had. Is that just the way the Rose is supposed to taste, or can I assume I had a bad bottle?
I don't know what to tell you except that I don't know of any way that a leaky cork would cause lactic acid to dissipate (since your description indicates that it wasn't very sour at all.)
The Rosé is pretty good Framboise beer but compared to the Jester King Atrial Rubicite, it can't compete. It's a solid beer but as you've suggested, I do not think it's very sour. Although they advise you to drink it fresh for max fruit taste, I like this one with +1 year of age on it. It has nothing to do with a leaky cork though. There's always a cap as additional seal. The corks Cantillon uses can sometimes be a pain in the ass as they are often very 'crumbling'. I even had this issue with a batch '14 Fou.
I've had a bad bottle of 375ml Rose from 2013, don't recall the bottling date though, tasted rather stale without much fruit flavor at all
it's fruit forward when fresh, with several years age the funky lambic characteristics start taking over. but if you're having it in the first year or so it's not going to be particularly tart.
Having started to cork & cap some of my homebrews, I've found that this is usually not caused by a leaky cork but by a slightly overfilled bottle at corking time. I've managed to get "very Cantillon" puddles of beer on top of some of my corks. Easy enough for me to tip out/wipe up but on a production line...
Putting aside whether you actually had a bad bottle or not, Im confident in saying that if it was a bad bottle, the leaky cork had nothing to do with it. That happens quite often with Cantillon bottles.
Perhaps trying side by side with Raspberry Tart will change your mind? These tastes totally different, even when fresh.
Glad I'm not the only one with leaky and crumbly corks. Every time I open a Cantillon, which is not often, the corks have crumbled and barely held on.
Okay, so it sounds like I had nothing to worry about with that bottle, I guess I should just have tempered my expectations. I had Vigneronne from the bottle a few weeks ago, and that was an explosion of flavor. I hope the bottles I have (Gueuze Lambic, Kriek Lambic, and LP Kriek) are ok...
Every bottle of the "Belgian Flag" gueuze I've opened so far have been kinda flat both in flavor & carbonation.
I bought 3 (375ml) bottles of Cantillon Kriek Bio in Vancouver, 1 of those had a leaky cap/cork and noticed it also was less acidic than the other bottle I had earlier that week. As soon as I popped the cap to the cork, it was full of liquid but the carbonation seemed fine.
