Why might this milk stout taste sour?

[invivoSaccharomyces]

I'm hoping to figure out what might have gone wrong with this milk stout. The kicker is, I didn't brew it. My buddy did. So I don't exactly know how it was brewed, except that it was brewed with an extract kit with steeping grains.

I know that infections can turn a brew sour. I exchanged my buddy for a few of these stouts, and I've been aging them for about a month. The flavor has barely changed since then. If it were an infection, I would think the flavor would change over time.

It also might be worth noting that the beer has zero head even though carbonation is just right, and it tastes thin and not very stout-y (i.e., almost no roast flavor, maltiness, etc.).

Is there anything else that can turn a stout sour? I'd rather ask here than confront my buddy with a "hey dude, your beer sucks" chat, at least for now. I'll probably be aging the remaining beers from this batch, just to see what happens. It isn't bad, it's just... not what the recipe calls for. I'm hoping my (intentionally) soured stouts turn out tasting a little more stout-y.

 

[ong]

I've had Nottingham get kind of tart when fermented too warm.

 

[BigFloyd]

If you don't know the brew details (especially fermentation and sanitation), what we could tell you here about it would be just speculation.

 

[invivoSaccharomyces]

I've had Nottingham get kind of tart when fermented too warm.

That could be it. I don't know if my buddy used dry yeast or a smack pack, though, and I don't recall if this was made before or after he bought a fridge for fermentation control.

If you don't know the brew details (especially fermentation and sanitation), what we could tell you here about it would be just speculation.

Yep! Of course, even if I had all the details of the beer's production, it would still be speculation. It would just be moderately more informed speculation. Regardless, speculation is exactly what I'm asking for.

I believe this is the kit that was brewed: http://www.wineandhop.com/beerRecipes/Elsie'sCreamStout.pdf