For 4 people
Pour the apple juice into a 2-liter glass jar.
Wash and cut the apples into pieces and add them to the jar.
Cover the jar with cheesecloth and a rubber band to allow air to circulate.
Let it ferment for 5 days at room temperature, stirring twice a day. A white foam should form at the end of fermentation.
Separate the juice from the pieces and pour it into a plastic bottle. Seal and let it ferment for another two days, degassing daily.
Once the bottle has hardened and swollen, refrigerate it for a few hours before tasting.