It’s possibly due to the temperature rising too high or getting too low in the first 24 hours of fermentation.
It’s important to note that yeast activity can raise the wash temperature by as much as 8°C (46°F) in the first 24 hours of fermentation.
It’s essential to start the wash at around 20°C (68°F) and not use any heat in the first 24 hours. If the wash overheats during this period, the yeast may not have the energy to finish fermenting.
If this has occurred, first stir the wash vigorously to stir the yeast back into circulation. If the SG has not lowered within 24 hours then obtain an EC1118 Wine Yeast.
As there is alcohol present you should first start the yeast working in 200mls of water. Once the yeast has dissolved, add 1 tsp of dextrose. When this is fermenting, add 200mls of wash. When this is fermenting add half of this back to the stuck wash and top back up with wash. Continue this until the wash starts fermenting.
Alternatively, it may be because the wash has cooled down below 15°C (59°F). In this case, warm the wash up and stir vigorously to get the yeast back into circulation. Once the wash is warm, fermentation should continue normally.