What are these white things that formed in my white grape juice? (Pictures included)

[winemaker012]

I poured 20 liters of white grape juice that I usually ferment. But I kept it in the carboy alone without yeast (just pure juice) for a few days and it was covered. I came back and found these white things. What are they? Should I throw the juice away?

 

[Ohio Bob]

Hard to say for sure, looks like skins from the grapes, might have some mold growing on them.

Why did you put the must in a carboy, and not the preferred method of fermenting in a bucket? Did you add potassium metabisulfite (aka Kmeta) at a rate of 1/4 tsp per 5g? If not, then you should have added yeast immediately.

So I would rack to a bucket, not pour it. The goal is to try and separate out that bad stuff. Add Kmeta at the rate suggested. Make a yeast starter (use the search function on this site or search on @winemaker81). After approximately 8 hours, add the yeast starter. This time will have given the Kmeta a chance to knock down the bacteria while your yeast starter is building a huge colony of yeast. When you add the yeast starter, the generation of alcohol and CO2 will stamp out the remaining bacteria.