Originally Posted by KevinJ
How are determining refermintation? A hydrometer or if bubbles appear?
Yes, hydrometer and/or if bubbles appear.
Bubbles aren't a reliable sign of fermentation- bubbles can happen for any number of weather related resons, for example. But if there is significant bubbling after sweetening and there wasn't before, that could be a sign that the sorbate and sulfite didn't quite finish the job and fermentation restarted. A hydrometer, over a couple of days, will confirm.