6. Seal the bottles and leave them out to ferment for 1-5 days, depending on how fizzy you like it. There is some danger of the bottles exploding but that’s never happened to me. I would start with a 2-day second fermentation for your first batch and lengthen the second fermentation the next time around. Once the second fermentation is complete, put the bottles in the fridge and enjoy at your leisure. I would recommend not opening the bottles until they have been in the fridge for a few hours, to minimize any fizzy explosions.