Why would sparkling wine only carbonate halfway??

[lukebuz]

I had some 13.5 Apple wine; I added 1.6oz gallon of priming sugar, and a raging Premier Cuvee starter. Bottled and capped it up, then left them. I noticed significant sediment formed, like it should, but my PET bottle never got rock-hard (like usual; I've made 4x similar batches before!). So, I left them a few more weeks, and unfortunately, when opening one, they have a good "hiss", and ever so slight effervescence, but no real carbonation.
So, it started, then stopped, and never went.
They were dark, warm, etc etc....
What could have happened??

 

[bernardsmith]

What was the recipe? What was your process? Might you have inhibited further fermentation before you added the sugar (and the sediment dropped out of the wine from the earlier fermentation? ). What was the SG when you bottled? What is the SG today? (if the sugar did not ferment it should have raised the gravity just over 1.5 points). Wine has no protein so effervescence is what you should expect and not a head (compare a sparkling wine to a beer)

 

[lukebuz]

SG was .99x prior, and .995 when I unbottled. It has some sweetness to it, so I know the sugar is still there (plus SG is high). It did have some bubbles, but like maybe 1 volume of CO2, so it only fermented about 1/4, if I guessed.
I did put the bottles on a heating pad that hits 117* on the pad - but it only heats the bottles to about 75*. I've used this on my carboys before. No problems. Perhaps the 117 could have killed off the yeast? Just hypothesising...

 

[Yooper]

You may have reached the yeast's alcohol toxicity point and the yeast just won't do anymore.

 

[bernardsmith]

That sweetness is not from unfermented sugar, IMO. A gravity of .995 when you opened the bottles suggests virtually not enough sugar for you to perceive "sweetness"...The sweetness may be the flavor from the apples themselves which you are mistaking for "sweetness"... so I suspect the answer to your puzzle is to be found in your recipe and the processes you used in fermentation