This ginger beer is very spicy. Adjust the amount of lime juice and sugar to your taste.
Place ginger in the bowl of a food processor, and process until finely chopped. Transfer to a large pot or bowl, and add the boiling water. Allow to standfor 1 hour. Drain through a fine sieve lined with a double thickness of damp cheesecloth. Discard solids. Add lime juice and sugar, and stir to dissolve.