■ 🕑 6. 
   Dry = all the sugars have been fermented by the yeast to Co2 gas and
   ethanol, basically. And they produce a lot more co2 than you'd expect! 
   The contrast to dry, in the context of wine, is sweet: which makes the
   meaning of "dry" more clear. 
   
   There are a number of ways to determine whether dryness has been 
   accomplished, fermentation has ended. 
   
   The easiest way is with a hydrometer -- when the specific gravity drops 
   below 0 (eg that of water), most likely all the sugar (which is more 
   dense than water) is gone and has been replaced by ethanol (which is
   lighter than water). Especially when the standard gravity is below 0 and
   remains constant for several days, that's a sign the yeast have finished
   consuming alcohol, and are now cleaning up after themselves before they
   go dormant and the hooch clears up. 
   
   Co2 can still be released from the liquid after fermentation has ended 
   so it's not a 100% sign that fermentation is still ongoing if Co2 is 
   being released. 
   
   For me, where ambient temps are 25-32*C, it takes about a week for 5%
   ABV to ferment with bread yeast (~85g sugar/liter) and then about 
   another week for things to settle out. Higher ABV takes longer to 
   ferment and longer for yeast to clean up after themselves. And you lose
   flavor. 
   
   A cheaper way to see that fermentation has completed: when your airlock
   goes inactive (either stops bubbling if it's a proper one, or the 
   balloon goes limp and deflates completely, if you go the balloon route)
   screw a lid on. Check every few hours for the next day to see if 
   pressure is building up: squeeze the bottle to see if it's gotten
   firmer and unscrew the lid to "burp" out any Co2 (you don't want a bomb
   going off) 
   
   When you test the bottle and no more Co2 is being released in 
   significant ways, after 2 or 3 days of checking, you can move onto the
   next step. 
   
   This is the time when you want to add 5g/liter of sugar and possibly a 
   dash more yeast before sealing the bottle and letting it sit -- I think 
   10g/liter could be feasible, especially in a plastic soda bottle for a 
   heavy carbonation. But you're going to have to wait at least another 
   week or two for the yeast to clean up after themselves and go dormant, 
   making the drink safe to drink, even though it's only the bit of Co2 
   you're looking for. Using clear plastic bottles is a great way to check
   "finishing" because the drink will become very clear when it's ready
   to drink. When in doubt, wait more -- it only improves the product! 
   
   All you can really do is trial and error if you don't want to research
   about the finer details of carbonation or invest in more equipment. I 
   think 5g/yeast per liter once fermentation is probably a safe starting
   point. Otherwise, double the ginger and ABV, then cut with soda water
   when it ferments dry. Takes maybe 2-3 weeks for a drink to be drinkable
   after starting fermentation, but more time only helps in making things
   smoother and more subtle. 
   
   Whether you add more sugar at the end to produce carbonation the old
   fashioned way or you plan to mix your dry fermented ginger ale with
   soda water, make sure to pour slowly from your fermenter -- near the end
   you'll see the nasty "lees" (dead yeast and crap), you don't want any
   of that in your final product because it tastes foul and can give you
   a tummy ache. 
   
   I'm only an amateur brewer & distiller but I hope this knowledge can
   help you. Feel free to update this thread with the results of your 
   experiments. Try to keep logs: date fermentation starts, recipe, 
   ambient temperature, date fermentation seems to end, etc etc. Brewing
   is an art and a science: either way, notes help.