Make your own homemade ginger beer. You'll need to start this recipe 8 days ahead.
You'll need a 20cm-square piece of muslin cloth.
Make Starter: Place yeast, sugar, ginger and warm water in a jar. Whisk with a fork to dissolve yeast. Cover with a tea towel. Set aside overnight at room temperature. Stir in 1 teaspoon extra sugar and ½ teaspoon extra ginger. Cover with tea towel. Stand overnight. Repeat process with remaining extra sugar and ginger for the next 3 days.
Make Ginger beer: Place sugar and 3.75 litres cold water in a large saucepan. Stir over medium-high heat until sugar dissolves. Stir in lemon juice.
Line a fine sieve with muslin. Strain yeast mixture (see notes). Stir into warm sugar syrup. Divide mixture among three 2-litre-capacity plastic bottles (see notes). Seal. Set aside in a cool place for 3 to 4 days. Refrigerate. Use within 2 weeks.
Keep the paste that's left in the muslin to use as another starter.
When filling bottles, leave a space of about 5cm from the top of the bottle to allow the ginger beer to expand. Use plastic bottles to prevent the bottles from breaking. Open the bottles every couple of days to ease the pressure build-up.
You could also serve the finger beer with a sprig of fresh mint for a lovely flavour twist.