Bubbling kombucha cocktail

Method

1. To make the kombucha, boil 1 litre water and let it cool slightly. Pour into a large glass jar, add the sugar and stir until it has dissolved. Add the tea and steep for 15 minutes.
2. Remove the teabags and let the mixture cool to 25°C. It is important to measure the temperature – if it is too hot you will kill the mushroom. Place the kombucha mushroom and culture in the cooled tea mixture, cover with muslin, secure with the rubber band and keep in a warm room (temperature around 23–25°C) for 8–14 days. By this time it will probably have produced a baby mushroom on the surface, small bubbles will start to show and the liquid will taste vinegary. If it is still very sweet, leave it for another week or so.
3. When ready, remove the baby mushroom and the mother mushroom using a wooden or plastic spoon (do not use metal), and rinse under lukewarm water. Place each mushroom in a separate glass jar together with half a cup of the kombucha culture (the one you just made) and cover. Pour your newly brewed kombucha into bottles and store in the fridge for up to one month.
4. To make the cocktail, mix the measured kombucha and apple juice in a large jug with the ice. Crush half the rhubarb slices with the back of a knife. Stir all into the jug and serve straight away.