Dark beers are sour apple, light beers are awesome. What gives?

[Earendil]

I've now done two light beers (both WITs), and 4 dark beers (a porter, two stouts, and a RIS).

Both the WITs turned out awesome. The porter was "meh", but it tasted finished. The two stouts and the RIS all taste unfinished after a good length of time, and there taste profile hasn't changed in 2 months.

The RIS was aged for 2 months, and has been in bottles for 5. The Stouts were "aged" a little over a month before bottling, and have been in bottles for 4 months.

I believe the RIS and Stouts taste like green apple and not wild-yeast-sour. This implies that the yeast in the bottles just isn't able to finish the beer, right? Or would you expect a 5% stout with a FG of 1.016 to need longer?

The RIS by its nature I'm not expecting much of yet, but given that the off flavor is also in the two stouts, I'm sort of not hopeful

Also, the Porter was my first good beer, and the light beers were brewed between the RIS and stouts, so it's not as if my process has "improved" or I had a bad environment. Except for that early porter, the divide between good and bad is based on color and that makes no sense to me.

Is there anything to "dark beers" not being able to finish ever? Is it a more destructive environment for east? I'm just wondering if the stouts will ever recover.

Or am I mixing up correlation and causation, and that it's my dark beers that taste like green apple is just bad luck?

 

[Earendil]

I meant to add:
Going through my brew logs I can see that the light beers and the porter were all bottled within a couple days of hitting the target FG (and FG not changing). The Stouts and RIS I was happy to forget about for a long time. One of the stouts sat for 34 days prior to bottling.
Is it possible that after that much time I don't have enough viable yeast to finish the job in the bottles?

Otherwise I can find little difference in my brew process.

 

[chickypad]

Having a problem with only light beers or only dark beers suggests a water issue to me. Since you're extract brewing mash pH wouldn't apply but I wonder if the dark grains in low alkalinity water could bring the final beer pH too low resulting in a sour/tart effect. Maybe one of the water experts will chime in.