My first AG turned sour; any ideas why?

[Betkefest]

Brew day went okay. 10lbs of grain, 1/2 lb of crystal, 1/2 pound of Munich. 70% efficiency, a little low but equaled a 1.05 OG. 4 oz of assorted hops. Wyeast London Ale yeast.
Then the problems started. A very slow fermentation. After 10 days a faint sour smell coming from carboy. After two weeks gravity was still well over 1.02. So I racked to a secondary and waited. Finally after a month a FG of 1.02. But the beer smells and tastes sour, a little like alcoholic orange juice.
I've done half a dozen extract brews, with no infections. A more experienced brewer friend suggested I bottle, just to see if the taste settles. I'm not optimistic. I bottled tonight, and I expect to be dumping this beer in a month.
I don't know why the fermentation went so slow. My basement temp is a steady 70 degrees. A liitle warm but okay for ales. But I think the slow fermentation allowed bacteria to grow, creating the sour beer.
Luckily my Oktoberfest beer is fermenting vigorously, so my next batch should be fine (knock on wood). But is there any chance my sour ale will be drinkable?

 

[Betkefest]

After a month FG was 1.01.

 

[manticle]

There's every chance your brew will be drinkable but it depends on a couple of things.

The first is - do you enjoy any deliberately soured beers? flanders Red/brown, berliner weiss, lambic/gueze/faro etc? If not then you possibly won't enjoy htis one.

The second is the level of sour (and how much is too much for you -see above)

The third is - why is it sour? What microorganism took hold and made it taste so? If it's one that doesn't produce any other negative flavour characteristics then it might be well and good.

The fourth is - is it actually sour? Is it bitterness you're tasting and mis-describing? How trained is your palate? Has anyone else given you an unbiased opinion (ie make them taste it and tell you their impression without prompting).

Sour can come from infection - lactobacillus and acetobacter are both possible culprits. Lacto can give a nice level of sour depending. Aceto will be vinegar sour - to me far too harsh to be enjoyable though some people don't mind as much when deliberately soured beers get an aceto character.

Brettanomyces strains can also impact on sour flavours - these are the wild yeasts present in Belgian wild beers, some wines and some old versions of english ales (including porters but you'd struggle to find it in any now). They will add some other funky flavours.

The thing to watch though is - a lot of these things are slow workers but will eat anything. That beer you thought should be finished at 1010 might get down to 1000 with brett but it might take a year. Keep the bottles away from children, pets and eyes (maybe wrap in plastic wrap) and valuable carpets. Leave for a bit and monitor, crack one each month and see if it's getting overcarbed or more and more sour or just plain horrible or wrong tasting. It won't kill you and may open up your palate to concepts of wild brewing, alternatively it may taste like arse and just be a lesson in infections and the depressing results when they ruin your beer.

Lag time/ineffective yeast sounds like the culprit. Don't be disheartened if you did get an infection. It doesn't make you a 'bad' brewer. Did you make a starter? Was it active when you pitched? Was the cell count high enough?

 

[Betkefest]

My palate's pretty good. I like sour Saisons and Berliner Weisse, and I appreciate lambics. If the beer is infected, I'm pretty sure this is a Lacto infection, because it doesn't taste or smell like vinegar. The ale is also heavily hopped, so perhaps the hops are contributing to the "off" sour flavors, and will mellow.
My friend who encouraged me to bottle anyway likes the Belgian beers, so I'll get his opinion when I open one up in a few weeks.
And thanks for the reminder about over-carbonation. I'll put these bottle someplace out of the way, and maybe even throw an old blanket over them for safety.