When I make a kit, I stir vigourously before pitching the yeast to ensure that the bentonite is well mixed, and that the juice/concentrate and water are mixed well. I have read that a good stir introduces sufficient O2 into the must. I stir gently every day ot two if there is something floating (grape skins, elderberries, elderflowers, oak tea bag). Once the fermentation starts, the action of the CO2 helps to keep the bentonite and yeast circulating.
the procrastinating wine maker in the Niagara Region of Ontario Canada
"Visual signs of fermentation are highly overrated"