Can I pasteurise part-brewed possibly infected wine and repitch yeast?

[friendlybrew]

Hello! First post but I've been reading this forum a lot for the last year. I am making a 20 litre batch of red wine (adding a few litres of grape juice every few days to keep the sugar levels at the right level) and have run into a problem. With the carboy about half full I had to leave for a couple of weeks. In this period the yeast consumed all the sugar and seems to have completely stopped fermenting. I further noticed that the airlock was not airtight. I tried adding another few litres of juice but after 2 days it has not restarted. Worryingly I spotted this evening strange white spots on top of the wine. Sadly I suspect it has become infected while exposed to the air without any carbon dioxide blanket to protect it. Therefore I plan to pasteurise the wine to about 70 degrees to kill the infection, if there is one, cool, rack to a new clean carboy and repitch fresh yeast. I will heat the wine in a lidded pot to minimise alcohol loss. Does this sound like a bad idea? I considered just using Campden tablets and repitching the yeast after a couple of days but I don't think this will completely kill the infection. As the wine is only part fermented I assume oxidation is not a problem when transferring into the pan and then into the new carboy. Any suggestions? Thanks!

PS photos of the wine attached.

 

[pumpkinman2012]

First, why did you add juice as you were going along?
Normally, you would add all of the juice, lets say for instance, 5 gallons, then pitch the hydrated yeast and let it ferment to dry, by letting the yeast ferment and essentially run out of any kind of food or nutrient, then adding more juice and probably over loading the yeast with sugar from the newly added juice, you probably stressed the living heck out of that yeast.

Where did you learn to do this?

The next big issue was leaving a carboy half filled with must/wine, with that much head space, It sounds like you've got mycoderma floating on the surface. This is will eventually spoil your wine if you don't do something about it quickly.
I would stabilize with meta (potassium metabisulfite) asap, a 1/4 tsp of meta diluted in a little water added to 5 gallons of wine and stirred.
Does the wine smell at all?
Have you tasted the wine?
I wouldn't pasteurize the wine, I do not believe that it will help you, plus I believe that you would need to reach a higher temp, essentially ruining your wine in my opinion.
What is the current SG?
I would stabilize with meta (potassium metabisulfite) asap

The wine isn't fermenting anymore because the yeast is most likely all dead and has dropped out of suspension, depending on the SG you could try adding a little more yeast, but I would cut my losses with this batch and drink it if it smells and tastes good, and start another batch that we can help you follow some basic steps that would make you a decent wine.

I hope that this helps

 

[Mr_fleabite]

You've taken a very unique route in your method of winemaking. I would not attempt to pasteurize and re-ferment. Taste a sample from in between the infection on top of your wine and the lees below. If it's drinkable, siphon it off leaving the mold & lees behind, SO2 the salvaged wine, drink it sooner rather than later and consider yourself lucky. If it tastes bad, dump the whole thing sanitize your equipment and start all over.

When you begin your next batch ferment all of the juice all at once, after initial fermentation, siphon it to another container off of the crud that has formed on the bottom of the fermentation vessel (ensure this 2nd container can hold nearly all of your wine, this means no "head space" or very little surface area exposed to air). If necessary top up this 2nd container with juice/ concentrate (some fermentation may start up a little). Wait a day or 3 if no fermentation is taking place add SO2. At this point you're essentially done, other threads can carry you though the gory details but this covers the basic start of "traditional" wine making.