Sour flavour after fermentation

[kirkcaldybrewer]

Hi all, me and a couple of friends recently brewed and split a batch of pilsner-style wort. In the end, this was sub divided into 4 batches each with different yeast and fermentation conditions.

I had two batches: 1 lager yeast (M76), one a saison yeast (wlp0566). The lager got the fermentation chamber set at 10C and tastes like a nice neutral lager.

The saison was just left on a bench top in the garage. I tasted it after 1 week of fermentation and it was normal.

But then I left for a two week vacation during which the beer experienced the hottest summer in recorded history (this is in Sweden). Temp isn’t recorded, but it could have been hot. And when I got back...it has a clear sour taste. Not unpleasant actually, but definitely sour.

Now batch number 3 was pitched with 34/70 and taken by a friend on a camping trip around Greece. His batch definitely hit 40C at some point. It’s also sour. (No obvious trace of fusels etc that would be expected with high temp)

Finally, the last batch was pitched with m79 and kept at sensible 20-22C. It is also not sour.

So question: could the high temp induce a sour flavour in fermented wort sitting on trub?

Everything I’ve read suggests this is normally due to bacteria, but then how could it affect two completely separate fermentations and leave the other two unaffected?

Thanks!

 

[kirkcaldybrewer]

I have just come up with another theory: the sour batches were both small ~5L. Is it possible that this is so small that it didn’t dilute the starsan I used enough sufficiently, so it left a sour taste?

When I tasted my saison is was in the fermenter. I only tasted it again after kegging and it was sour. Perhaps the starsan I used to sanitise the keg caused it??

 

[Pappers_]

At high temps, yeast can produce a lot of compounds, that can combine with each other and with other flavors in the beer to give the impression of all sorts of flavors. I wonder of what you're perceiving is some hyper strong esters, that your brain associates with sour fruit? Its just one possibility.

Another is that there is an actual wild yeast innoculation and the high temps put it in overdrive, while the lower temp batches have kept it growing very slowly.

 

[hottpeper13]

Being from Wisconsin 5 liters would only last a couple days, not really enough time to see if time makes it worse. If it gets more tangy with time it prowlley is contaminated. I think star san would have to be high concentration to cause this. You could check the pH, it would have to be less then 4 to give it that tang.

 

[kirkcaldybrewer]

I just did a test with the (not sour) lager batch.

I took 200ml lager and added:
0.5ml dilute starsan: no change
I increase to 1ml: no change
Then
5ml: no change
10ml: no change
25ml: still no change

At this point it was almost 10% starsan and still no sourness.

I think I disproved my second theory.

 

[kirkcaldybrewer]

So, it sounds like I should take a sample of the lager, warm it up for a couple of weeks, and see if it develops a sour tang?