The difference between alcoholic and non-alcoholic is all a matter of sugar (and time).
Here are the directions from a commercial home brew pack (900g of mostly malt which is a type of sugar) makes 23 litres:
For ALCOHOLIC ginger beer:
- Add 4 litres of HOT water (not boiling), contents of Home Brew Pack, and 1kg of raw sugar to sterilized Fermenter, dissolving thoroughly.
- Add an extra 18 litres of cold water. When the temperature of the brew is 35C or less sprinkle in yeast and nutrient. Seal Fermenter.
- After fermentation has ceased (after approximately 6 days at 25C, AND when hydrometer reading is between S.G 1.005 and 1.000), add 1 heaped teaspoon (7g) of sugar to each of 30 x 750ml clean and sterilized bottles. Fill, seal and store bottles for a minimum of 3 weeks.
For NON-ALCOHOLIC Ginger Beer:
- Add 4 litres of HOT water (not boiling), contents of Home Brew Pack, and 150g of raw sugar to a sterilized Fermenter, dissolving thoroughly.
- Add an extra 18 litres of cold water. When the temperature of Brew is below 35C, vigorously stir yeast and nutrient into brew.
- Seal fermenter and leave for 2-3 hours, stir brew gently and then bottle. DO NOT ADD SUGAR TO BOTTLES. Store bottles for a minimum of 3 weeks before drinking.
So, from the above we can see the only difference between the alcoholic and the non-alcoholic versions, in the ingredients, is the amount of sugar added.
This makes sense because yeast eats sugar and produces alcohol and carbon dioxide (CO2), so the more sugar you add the more alcohol you produce.
For non-alcoholic ginger beer you need to walk the fine line between enough sugar to produce enough CO2 to give the ginger beer its fizz, but not enough to make it alcoholic.
The long ferment in the alcoholic version is to allow the yeast to convert all the sugar into alcohol while allowing the CO2 to escape, then the sugar in the bottle is for the yeast to convert into CO2 to provide the fizz. While the non-alcoholic version is bottled almost immediately to trap the CO2 in the bottles for the fizz.
There are a number of recipes for non-alcoholic ginger beer on the internet and they mostly seem to say 1 cup sugar per litre of water. This is much more than the amount required in even the alcoholic version of the directions above. Which explains why my ginger beer always turns out alcoholic, even if I put it straight in the fridge, using those recipes.
For non-alcoholic ginger beer you want more like 1 cup of sugar per 20 litres of water, or better yet just add a teaspoon per litre when bottling. The same yeast is added to both versions, so you can buy a commercial starter, or use a home grown ginger beer plant for either alcoholic or non-alcoholic ginger beer.