Possible reasons why my beer went sour

So I've been making double batch in a day, one BIAB and one on Grainfather both about 7 - 8 litres. One was Amber Ale and the other Saison. Everything went fine and I splitted a packet of Safale US-05. Yeast was pitched at 25°C and fermentation was 18 - 21°C. Both weren't opened since there is no dry hop.
What could go wrong?
I'm suspecting bad yeast since both fermenters were brand new and beer remained closed til bottling day.
Only thing connecting both beers is yeast and same brew day.
Thanks for your anwsers!

 

Very sour like vinegar or just a little sour like green apples?

 

Sour tasting like wine.

 

It sounds like a bacterial or wild yeast issue. But I am also wondering if you put a large amount of sugar in these recipes? Can you let us know?

 

No sugar added both should be at around 6% alcohol. I'd take wild yeast infection but it just seems weird that it would happen in 2 of my fermentors out of 8 that were filled at the time and on the two that weren't opened since pitching yeast since all others were dry hopped.

 

What kind of vessels are you fermenting in? What is your sanitizing regime? Do you clean them after each brew with a cleanser, or just rinse?

Just because it hasnt been opened doesn't mean it couldnt be a contamination. Could have been something lingering there already that survived or otherwise slipped past sanitizing.

 

It were brand new plastic fermentors, cleaned with boiling water, later rinsed with StarSan. There couldn't be anything from before since they were new.

 

Just because they were new doesn't completely eliminate the possibility, but I agree it is unlikely. My only suggestion is to try to make the best of the situation. Move the soured beer to a secondary vessel with limited headspace like a glass carboy if you can. Let it sit for as long as you care to. Might turn into something beautiful...might turn into vinegar. Who knows? Anyway after you get the beer out of the bucket closely inspect the bucket for marks, dings, scratches. Anything that could harbor contaminates. If they are damaged in that regard don't use them again. Honestly I wouldn't use them at all either way but that's your decision to make.

 

Just gonna use bleach and water on everything and the beer already went down the drain since it was badly sour not nicely sour

 

Shame it didn't turn out. Better luck next time. Make sure you rinse, rinse, rinse all that bleach out really well!

 

Bleach does not clean, it only sanitizes. And only a clean surface can be sanitized.

You need to use a cleanser like OxiClean, PBW (Powdered Brewery Wash), Alkaline Brewery Wash, etc.
Ideally you follow that with a water rinse and then an acid rinse.