Disappointed in the commercial ginger sodas, I have set out to do my own. I think I have it close to what I am looking for. I thought I'd share even though it's not that different from what others are doing.
This is for 2 liters:
7oz fresh grated ginger
Zest and juice from 1/2 lemon
Zest and juice from 1/2 lime
1/2 cup white sugar
1/2 cup dark brown sugar
1/4 tsp Red Star Pasteur Champagne yeast (might be able to use just 1/8 tsp)
Add ginger, lemon, and lime to sauce pan and cover with 24 oz of good water. Simmer until liquid is reduced by about 1/4 or so, or a good 30 minutes. Strain and squeeze as much liquid from the remaining pulp as you can. Add liquid back to sauce pan and bring back to boil adding sugar until dissolved. Allow to cool and pour into a 2 liter bottle. Add water to fill bottle 3/4 and add yeast. Cap and shake. Loosen cap and squeeze the headspace from the bottle and tighten cap again. Let sit in a warm spot until the bottle is rock hard (less than 24 hours in my experience so far) and then place in the fridge.