Sparkling wine fault

I made a small 5 gallon batch of sparkling Petit Manseng that has turned into a gusher. The small test batch that I made the year prior also ended up the same way but took longer to get to this point. It looks exactly like my experiences with my first few batches of beer many years ago before I got control of sanitation. Therefore, I assume it’s a sanitation problem again. Except what I can’t figure out is why It’s only an issue with sparkling wines. I’ve made a lot of still wine without any issue and while I haven’t made beer in years now, the ones that I did make after fixing the sanitation issue have been fine. I still have some bottles pushing a decade old that are stable.

I should also note that after the first gusher yesterday, I opened a second bottle to confirm and while both did gush, one had a noticeable sour taste and the other tasted fine.

I didn’t force MLF prior to sparkling and I never verified that the base wine was completely dry. It tasted dry and it didn’t go under crown cap until June.

Any thoughts would be appreciated. The wife loves the wine and still drinks it and plans to continue making sparkling going forward so really would like to figure out this fault so I can eliminate it.

Could it be a miscalculation on sugar levels and still be under the bar pressure limit of the bottle after refermentation?

I’ve considered this as a possibility. After the issue with the first test batch, I checked multiple sources for the proper grams/liter of sugar to verify I didn’t add too much. It was within range but to be safe for the most recent batch I kept the addition to the low of the range. So unless multiple sources are all wrong or my scale is off, I don’t think it’s an addition problem. But as noted, there may have been RS in the base wine.

I’m also guessing too much sugar. Especially if it tastes okay after you dry off. I found when I was kegging beer that I was always over no matter what the scale called for. I just started cutting my sugar by 25% (if memory serves) and it magically started working.

Brian - What i did for the first time as a quickie experiment is I moved a 2-3 brix chenin blanc wine into champagne bottles to allow the fermentation to complete under crown cap. If I recall correctly that leaves me under 4 atmospheres for a bottle that can handle >8atm. This method produced nice fine bubbles that were controlled when opening crown cap.

Are you factoring in the temperature that you are doing your bottle conditioning at? You will need to use less sugar the colder that temperature is. The type of sugar matters also, ie. less sucrose vs. dextrose. Ensuring the wine is dry (or factoring in the residual sugar) before conditioning so your priming calculation is correct is important. Head space in bottle could be a factor. Also you could have some trapped C02 from fermentation affecting your calculation, i.e. you could be at 1 atm already. Whatever the case it is definitely too much sugar at bottling for your specific setup.

We have opened a couple more bottles since the OP and all while over carbonated taste fine. So it was only the one bottle that had a sour taste. It does seem to be a case of too much sugar and plan to cut down on the next batch. The wife is getting really good at opening these to avoid gushing so as to not lose any wine.