No bubbles is a sign that the yeast has done its job and the wine is made. Sometimes you can simply shake the secondary and the bubbles will start up again.
All yeast has a certain tolerance to alcohol, but at some level, the alcohol being created will kill the yeast and at that point adding more sugar will only sweeten the wine. When you add more sugar, you are doing so as a sugar syrup, generally 2cups of sugar to one cup of water, and doing so will dilute the wines alcohol content. Any surviving yeast can restart the fermenting process, again bringing the alcohol levels back up to where the alcohol will kill off the yeast. There are something like 5000 different strains of wine makeing yeast, each with varying levels of alcohol tolerance, each yeilding different alcohol percentages in the finished wine product.
Now this part is just my opinion, but if you are not getting any bubbles from your carbouy and stirring the wine doesnt create any more bubbles. Its time to sweeten to taste and continue racking until the wine becomes clear. That might take several months to let occcur naturally, but some folks use clearing agents and filters to speed up the process. At that point, put it in the bottle.
All yeast has a certain tolerance to alcohol, but at some level, the alcohol being created will kill the yeast and at that point adding more sugar will only sweeten the wine. When you add more sugar, you are doing so as a sugar syrup, generally 2cups of sugar to one cup of water, and doing so will dilute the wines alcohol content. Any surviving yeast can restart the fermenting process, again bringing the alcohol levels back up to where the alcohol will kill off the yeast. There are something like 5000 different strains of wine makeing yeast, each with varying levels of alcohol tolerance, each yeilding different alcohol percentages in the finished wine product.
Now this part is just my opinion, but if you are not getting any bubbles from your carbouy and stirring the wine doesnt create any more bubbles. Its time to sweeten to taste and continue racking until the wine becomes clear. That might take several months to let occcur naturally, but some folks use clearing agents and filters to speed up the process. At that point, put it in the bottle.