Normally I think I could answer this question on my own, but I'm having the hardest time figuring out exactly what I'm growing up from a Cantillon dreg.
It started with a 5 year old bottle of Cantillon kriek I received for xmas, shipped in from Belgium (so no idea on storage conditions). I had some extra wort from a brew, so I threw the dreg in a small mason jar with it and hoped to catch some yeast. A couple days go by... nothing... a couple weeks are gone and still nothing. At this point I figure it's a bust and am just being lazy about throwing it out. About 2 weeks ago I finally get around to throwing it out and for some reason I decide to taste it, BAM!, it's all tart. I focus in on the jar and notice there's a lot more sediment at the bottom than there was from the bottle, so something reproduced in there. It's still flat, no carbonation/bubbles, no pellicle... looks completely dead except for being cloudy. I've since added another starter from last week in the mason jar and tasted it tonight, and sure enough, it's tart as well. So what could this be?
I've heard lactobacillus doesn't have much of a shelf life. This would be my best guess because there are no signs of activity, and the sour is pretty prominent, but I don't think it would out-survive other organisms.
Pediococcus I don't have much experience with, but I've heard it pellicles pretty quick.
Brett I think would show an active fermentation.
Are there any other guesses or has anyone else grown up a Cantillon dreg with similar experiences? I'm considering adding it to my next beer with a vial of WLP644 and seeing what the outcome is.