Developing off flavour, possibly an infection

[Wirk]

I have been brewing for some time now but I had to stop completely for 8 months because temporarily I moved to an apartment, now I am back to a house so I want to start again.

Before moving I did three batches to have homebrew in my apartment...the thing is all the three ones started developing off flavours after some weeks of bottled. I usually try one of my beers at 2 weeks of bottled, 3 weeks and then I start drinking at 4 weeks.

All of them followed the same pattern, at 2 weeks they tasted green but promising, at 3 they felt like close to ready, at 4 weeks they started tasting off... at week 5 one was gushing and all of them had a bad flavour(the one less hopped specially)... at week 7 all of them were gushing and had an off flavour that made them undrinkable also the foam is very strange, it is extremely thick(I know thick foam is a good thing, but this one resembles yoghurt).

This sounds like an infection, right? What do you recommend me? cleaning everything with bleach? Change tubes?

It started so slow that I think it might be related to the bottling process (I do long primary, no secondary) but I am not an expert... is it possible that it started before?

 

[Wirk]

By the way I use light carbonation, I like more English like ales, also everything is all grain with fly sparge.

And about the off flavour, I can't describe it well... it is something that I know it shouldn't be there.

I've tried my brother and father to try it to tell me what does it taste like but none of them can identify what it is close to... they both just agree there is a strong bad flavour in it

 

[Kahless]

Yoghurt beer, interesting; If you can tame the off flavour down to nothing you could have a new mass market smooth beer! (J/K)

That sounds absolutely terrible though, tough luck.
Although it is developing in the bottles, the source of the infection may be from elsewhere; perhaps some beastie that lives but doesn't thrive, until it is in a nice anaerobic environment, maybe loving the CO2, Alcohol, and the less confident yeast colony of a bottle.

Have you asked anyone to look at a flavour wheel of off flavours and see if they can spot the flavour from that? (edit: here is one; Is it Catty, like... Blackcurrent Leaves apparently?) Might help in identifying the type of infection and the required sanitisation/replacement procedure (If you're like me you'll be wanting to get away with throwing away as little as possible while still getting the info you need to confirm that your next brew is going to be safe!).

I have heard that plastic can really pick things up though, and it may not be possible to remove every trace. For something that develops over the long term like that in the bottle, a small source can lead to a big problem.

If you do use the same equipment after some serious cleaning, you could try and pasteurise half the beer (see the Cider section I think) just at the very point of adequate carbonation (and no later!!!). The hops would continue to mellow and there should still be some conditioning of balance between the malt and hops despite the yeast not helping. In this scenario, at least half the batch would be okay.