Fill a gallon-sized jug most of the way up with spring or well water (do not use water from the tap unless your house runs on a well). This water should be room temperature or slightly warmer (aim for 70 to 78 degrees).
Stir the ginger starter well. Add 1 cup of the ginger starter, sugar, lemon juice, grated ginger, and the ginger starter. Stir very well. Cover the jug with a cheesecloth or towel bound by a rubber band and put it in a dark place at room temperature for 8 to 10 days.
Taste-test the mixture periodically to see if more sugar needs to be added (the natural probiotics will eat the sugar so if the beverage ever loses all of its sweetness, add a little more sugar (no more than 2 tablespoons at a time).
Stir the mixture once or twice a day. You will notice a white substance forming around the ginger at the bottom of the jug. The ginger beer is ready when the substance becomes bubbly when stirred (similar to when you’re making the ginger starter).
Once the ginger beer is ready, give it a taste test. If it doesn’t taste sweet, add additional sugar and ginger - once you bottle the brew, it goes through secondary fermentation and the probiotics will need more sugar to survive.
At this point, your options are to either bottle the ginger beer as-is or flavor it prior to bottling it. If you choose to leave the ginger beer as-is, simply transfer the ginger beer toglass bottles, secure the lids, and place bottles in the refrigerator.
If you choose to flavor the ginger beer, add your flavoring ingredients to the flip cap bottles (see blog post for flavor ideas and instructions for secondary fermentation) prior to filling the bottles up with ginger beer. Secure the lids on the bottles and leave at room temperature for another 2 days.
Place bottles in the refrigerator to calm the fermentation process. Note that the ginger beer will continue to ferment in the refrigerator, so try to consume the beverage within a few days after secondary fermentation is complete for best results. Leaving it in the refrigerator for longer than a week will result in a “drier”, less sweet ginger beer.
You can now brew another batch of ginger beer using the ginger starter you have been feeding. Because your ginger starter is now more mature, it will take a little less time to brew your second batch.