Bring to the boil the water.
In a large bowl, place the tea bags, all or some of the caster sugar (depending on how sweet you like it or the bitterness of your tea) and pour over the boiling water. Stir once or twice to dissolve the caster sugar., stir to dissolve the sugar and leave for 6-10 minutes to infuse.
Remove and discard the tea bags without squeezing them. Leave the tea to cool completely before pouring into a large 3-4-litre glass jar or clean container. Add the SCOBY and its starter liquid, leaving a minimum of 5cm space at the top of the jar.
Cover the jar with a cloth or kitchen paper so the SCOBY can 'breathe'. Secure with an elastic band and label the jar with the date and its contents.
Leave to ferment for one to two weeks at room temperature and away from radiators, the oven or direct sunlight.
After the first week, taste the kombucha daily – the longer you leave it, the more acidic the flavour will become. When ready, pour the kombucha into bottles, making sure to reserve the SCOBY and 100-200ml of starter fluid for the next batch. You can start a ‘secondary fermentation’.
Flavour with some berries or other in the bottle. Place in the fridge to stop the fermentation and it Will keep in the fridge for up to three months.