Why is my Porter Sour?

Hi guys! Longtime lurker, first time poster. I've made a porter and it turned sour. I'm trying to work out what the problem was as to avoid it in the future.

This was an all grain 5 gallon batch. Recipe was Northern Brewer's Saint Paul Porter.

8.5 lbs Rahr 2-row Pale
1 lbs Simpsons Medium Crystal
0.5 lbs Simpsons Chocolate Malt
1.5 oz Cluster 60 minutes
1 oz Cascade 1 minute
Safale US-05

This was made via the brew in a bag method. It went into the primary, a 5 gallon bucket on 11/8. The bucket was too small and there was a small blowff.

The batch went into the secondary around 11/15. At this time I was using two Mr. Beer fermenters for a secondary. They both had blowoffs. I cleaned them up and all seemed fine. There were no signs of infection. However, a few days into the secondary, the beer's smell turned from a roasty porter smell to a more sour smell. I thought at the time that it was residual yeast crude that was left all over the inside of the kegs.

The beer was bottled on 11/22. Every one I've tried since then has been sour. There's a strong sourness that hits the outer edges of the tongue. You can still taste undercurrents of the roasty porter that this was meant to be. The sourness has diminished a bit, but is still pronounced.

The beer has been in the bottle for a month and a half, so I think I'm past the green beer phase. The beer is strange, but I can still drink it. I'm just trying to figure out what went wrong so I can be sure not to repeat it in the future. I'm confused as to what caused the sour flavor as there were no signs of infection at all.

Also, just as a quick note, I have moved to a proper primary and secondary now.

Sour usually means contamination/infection. It's probably lactobacillus. It will probably get worse with age, unfortunately.

I'd suggest skipping a "secondary" (more properly called a bright tank or clearing vessel) as sometimes that is a source of contamination. I'd ferment in the fermenter for two-three weeks, then rack to a bottling bucket and bottle.

Did both Mr. Beers worth of beer sour? Or only 1? If they both did, there's likely somthing wrong with your sanitation regimen. If only one did, you would have to think that it was an issue with that Mr. Beer kit alone: not cleaned properly, or not sanitized well enough.

If you have moved on to proper fermentation vessels, then the second scenario is moot. If they both did sour, then we need to look at your sanitation. Anything that touches the wort post-boil needs to be dunked/sprayed off with a no-rinse (preferably) sanitzer like StarSan or Iodaphor. As a safety measure, you might even want to bleach bomb your equipment, making sure to rinse it really well.

If this is all your normal MO, then we'll have to look elsewhere. Do you crush your own grains? If so, are you doing it in the same area as the reast of your brewing? Bulk grains carry a plethora of nasties, and milling them can make the bugs airborne. When the dust settles into your wort, you're just asking for infections. Make sure your brewing area is relatively free of dust and grime.

Thanks guys. They did both sour. I assumed that it was probably lacto, but I hadn't seen any signs of it.

I've been using one step as a sanitizer. I know I should use an actual sanitizer like StarSan, but I'm moving soon and the movers won't transport it.

I get the grains crushed by Northern. And I have stopped using the Mr. Beer kegs. I don't like having the beer in there without a proper airlock.