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Krausen in bottle + carbed overnight after bottling = bombs?

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Narapoia

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Bottled my third batch last night. Same process as the previous two which turned out fine but this morning woke up to find that some of the bottles had what looked like a mini krausen ring on the top, which didn't look right. Popped the one with the most pronounced ring and it bubbled over (not exactly gushed but it was pretty keen). Definitely carbed.

Batch 22L
Final gravity after two weeks in the fermenter was 1011, stable for 3 days and bang on the FG based on the recipe.
I used 170 g of table sugar to prime in a sugar solution that was dosed per bottle by syringe so no mixing issues. Did the same for the previous two batches though with a total of 155 and 163 grams for batch 1 and 2 respectively and I upped it this time due to both of those beers being sufficiently carbed but under the level I am used to from commercial beers)
It was a Kolsch recipe I got form here but I used Fermentis Safale K97 yeast (Massive krausen in the fermentor but a slow ferment compared to the US05 I used in my previous batch)

I measured the gravity of the semi-gusher bottle = 1012
Cracked another bottle without a Krausen ring in it after chilling it. No gush, but definitely carbed - more so than the previous two batches that have had more than 4 weeks to condition. Waiting for it to stop bubbling to measure FG but the it looks about 1012 from the attempts I have made so far.

Kicker is that it tastes fine, no off flavours or aromas and tasted fine in each sample I took for gravity reading during the ferment. The one that I cracked after chilling is was great (I may have drunk another bottle that I opened to test as well, better than it exploding right.) Beer is a bit hazier than the previous batches in the bottle and when I was filling the bottles they generated a foam layer that I hadn't seen before.

Has anyone seen anything like this before? From what I have read it would seem I have an infection on my hands that is affecting the whole batch - so maybe a contamination issue with the bottling wand or spigot. No beer should be fully carbed like this is overnight is my understanding - I've put all the bottles in an esky and a hard walled crate for now. Should I dump them? If I had time I would just drink them but don't reckon I'll get through the whole 22L batch on a sunday.

Edited to add: Just tested another bottle - minimal carbonation and gravity 1011 - so maybe it's just some infected bottles. Frustrating. All were soaked with hot sodium percarbonate solution overnight, dried then sanitised with starsan prior to bottling.
 
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MHB

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It would take an unusual and massive infection to give that much CO2 that quickly.
More likely I think that the yeast was still working (primary hadn't really finished) and when you put in the extra sugar, roused the yeast and using a syringe probably aerated it some to, it took off like a rocket.

I would like to know more about your temperature control and were the bottles stored warmer than the ferment.
If your sugar was evenly distributed you have added ~3.7g/L of CO2 depending on the temperature you were storing your beer at you could have quite a lot more CO2 in solution than you expect. Given that - 3.7g/L isn't enough on its own to be blowing up bottles (well not pressure rated bottles)

K-97 is a very old yeast strain, one of the oldest still in production, its a fair bit more temperamental than its younger relatives (and in some cases descendants) it can sort of hover between working and going dormant at some temperatures. Then turn off or take off at a moments notice.

I would be tempted to cross my fingers, wait a couple of days, see if the beer gets enough carbonation, if it does get the bottles into a fridge as cold as you can and get into them.
Mark
 

Narapoia

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Thanks Mark.

I don't have anything sophisticated for temp control. Just a cold garage and a heat pad, I left it off the pad for 4 days and it dropped naturally from pitching to about 14 degrees in that time and the airlock stopped bubbling. Put it on the heat pad and the temp raised to around 17 for another week with FG dropping from 1017 to 1011. It stayed at 17 till a couple days before bottling, I took it off the pad and then it dropped to 14 it so, bright it inside and ambient raised it to about 17-18.

After bottling I kept it in the house which is 17-20 during the day and a touch colder overnight.

I aimed for the top of the recommended ale\lager range (5.4 g\l) as the previous batches I aimed close to the middle and found them a bit under carbed relative to commercial beer. Hopefully I just got some roused yeah and a bit more residual CO².

Got them all in solid containers, going to leave them and see how it goes I think given the range of experience with the bottles I opened so far.

I used mostly recycled commercial beer bottles for this batch and was planning to leave them to settle over the colder months but will play it by ear given this development. Thanks Mark, I'll crack another one in a few days and let you know.
 

Narapoia

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Just cracked a randomly selected bottle to test and no gushing, tastes great but far more carbonated than the previous batches I made at this point so I think your call is correct Mark. Thanks for the input, great learning experience and very happy not to have an infection and a ruined batch. Thinking back on it - the bottles that have been the most carbonated were filled towards the end of the process, probably got a bunch more yeast from the krausen and the trub and went to town.

A little disappointed with the K97 yeast though - the beer is really good, tastes like a clean lager but was hoping for a bit of the fruitiness you expect in a kolsch style beer. I have a half batch in the fermentor now with the same malt & hops but Lallemand Koln yeast and it tastes worlds apart. It was slow to get started and smelled like fruit punch while fermenting but the beer is much more interesting for it.
 
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