first hiccup - infection of overcarbonation?

[tonysbrewery]

Hi everyone,

Intro
First time i register in homebrew forums but usage of this (and other forums) as been religious and a constant for me.
I thank you for the amazing knowledge base this forum provides. It's in the same level as the literature out there when it comes to (home) brewing.

I've had my first hiccup in my homebrew hobby - i've been brewing for a year or so (4 extract and 5 BIAB AG). I would consider myself an expert beginner now!
All the brews have been coming up nicely and it's going really well. However, i had my first big hiccup one of the last couple of brews so i'm looking to understand what might have happened from your valuable experience.

Detail
I had two gushers out of 7 bottles opened:
3 of them were on fridge for 3/4 hours before serving and did not gush.
2 of them were on fridge for more 12-24 hours before serving and were gushers.
1 of them was on the fridge for more than 12-24 hours before serving and did not gush.
1 of them was opened without refrigeration and did not gush.

I degassed one of the ones that gushed and measured gravity. It was the same (maybe one point less) than the FG before bottling (1.012-1.011).
It tastes good but there is a tiny hint of sourness that is unusual in all of the brews i made up to now but this was my first time using Vienna (~20% Grain Bill) and using some Cascade hops i bought last year (they are stored open in freezer in a ziplock bag).
I always VWP and Starsan/Chemsan all equipment before and after brews (bottles/caps and brew equipment except boil kettle!)
What could be the reason for these gushers - true infection, uneven priming sugar mixing in wort before bottling,...? No ring or visible issues in the bottles.
I usually pour the priming solution in bucket then syphon the wort from the fermenter and let it swirl around.
Looking forward for your knowledge and opinion on this!

My recipe & fermentation details

Grain bill

3.70 kg	Simpsons - Finest Pale Ale Golden Promise		37	2.4	79.6%
850 g	Simpsons - Vienna		36	3.5	18.3%
100 g	Simpsons - Dextrin Malt		31	1.1	2.2%

Hops schedule

8 g	Simcoe		Pellet	13.3	Boil	60 min	15.77	9.3%
12 g	Cascade		Pellet	6.1	Boil	60 min	10.85	14%
10 g	Simcoe		Pellet	13.3	Boil	15 min	9.78	11.6%
15 g	Cascade		Pellet	6.1	Boil	15 min	6.73	17.4%
10 g	Simcoe		Pellet	13.3	Aroma	0 min		11.6%
15 g	Cascade		Pellet	6.1	Aroma	0 min		17.4%
8 g	Amarillo		Pellet	8.9	Dry Hop	4 days		9.3%
8 g	Cascade		Pellet	6.1	Dry Hop	4 days		9.3%

Mash schedule

17 L		Infusion	65.5 °C	60 min
8.4 L		Batch Sparge	20C	15/20 min

Used a 1/3 of a protafloc/whirlfloc tablet and Lalbrew Nottingham High Performance Ale yeast. 3 weeks in primary, 2 weeks in bottle.
OG - 1.060 and FG - 1.012 yielding 6.2% ABV.
I've packaged 13L primed with 88g of table sugar - aiming for 2.4ish carbonation level.

 

[smcc]

Do all of them taste sour? and is it just a hint or its undrinkable? I would lean towards uneven distribution of sugar solution as It happened to me a fair bit early in my homebrewing life. If you really had an infection I would expect all bottles to be impacted usually as bacteria multiply once they can get into something like beer. 88g is ok for that volume maybe a few grams over but not enough to cause gushers. I dont have any experience with that yeast to say whether 1.012 is a typical final gravity

 

[tonysbrewery]

Thanks @smcc !

Not all of them have the sour hint. They are not undrinkable and they smell amazing (not sure if infection plays a part on smell).

My point around the FG was to check if some unusual infection fermentation is taking place - by degassing one bottle that gushed and then checking gravity. That degassed sample hydrometer reading was within +/- 1 gravity points of the final gravity just before bottling. But i'm not sure if this is enough to rule out infection or not!

 

[smcc]

If it were an infection I would expect a much stronger off flavour and that some of them havent means its probably not that. As said I dont know how low that yeast will typically go usually you dont get much lower than 1.010 so I dont think those 2 points would cause gushers. Its been so long since I did bottle conditioning but its happened to me more than once. I guess just try to crack them a little to release pressure prior to drinking.

if you google beer off flavours you will get the typical ones associated with infection see if it fits any

 

[tonysbrewery]

Thanks @smcc .

I think i'm of the same opinion as you. I'll see how the next bottles behave and probably come back with more info.

I'll check Palmer's "nice" list of off flavours and see if any match aroma/smell. For me it's hard to pin point/match taste - my taste buds are not very good at distinguish that!

Thanks for your answers @smcc !