Hi. I've done natural fermentation with my dad since getting out of the Air Force in 2003, and every year we've done Concord grapes. We simply pick, stem, smash for about a week, strain, add sugar and put it in a carboy until March. It always comes out great! This year, we are also doing Niagaras, and I picked enough Niagara grapes to yield about 11 gallons of juice. Unfortunately, there was bad timing and some things came up at home and I wasn't able to get the juice strained and sugar added for an additional week. The upside to this is that it gave everything time to settle, and when I siphoned the juice off of the top, I ended up with relatively clear juice. The downside is that after adding the sugar and putting the juice in carboys, even after several days, there is no fermentation process whatsoever going on. I'm pretty sure the natural fermentation finished with the sugar that was present before I was able to get the additional sugar added. Is there a way to kick-start the fermentation process again? Can I add wine yeast at this point? Or do I just have 11 gallons of sweet grape juice? Thanks.