Bring two litres of water to the boil in a stainless-steel pan. Leave the water in the pan or transfer to a heatproof brewing jar. If using loose-leaf tea, put it in a tea ball and steep the tea of your choice for four to eight minutes depending on how strong you like the flavour, or brew your teabags.
Remove the tea ball or bags and using a wooden spoon, stir the sugar into the still-warm steeped tea to dissolve. Allow to cool completely to room temperature. Cooling the tea is imperative as adding the scoby to hot water will damage it.
Add the unflavoured kombucha or white vinegar, and with clean hands, gently lower the scoby into the cooled, sweetened tea with the paler side facing upwards and any yeasty strands facing towards the bottom.
Cover the jar with the cotton cloth and secure with an elastic band. Set aside at room temperature, out of direct sunlight, for at least seven days before tasting. You should start to notice a vinegary flavour as the scoby eats the sugar. Taste daily and when you find the perfect balance of sweet and sour, it’s time to bottle the kombucha ready for the secondary ferment. I often wait 30 days before it’s sour enough for my tastebuds, so don’t be afraid to leave it longer.
Decant into bottles, leaving about a 1cm air space at the top, then seal and refrigerate until ready to use.