Thoroughly clean a 1.5l PET bottle.

Add yeast, sugar and and about 1dl of water to the bottle using a funnel. Shake the bottle well.

Mix the ginger and the lemon juice, add to the bottle.

Fill the bottle with water, leaving about one inch of head space.

Close the bottle with its cap. Shake until all sugar is dissolved.

Let the bottle stand at room temperature until it feels hard when you squeeze it. This should take 24 to 48 hours.

Place the bottle in the refrigerator. Your ginger ale is ready once it is thoroughly chilled. Open the bottle carefully.

CAUTION: keeping the bottle at room temperature longer than is needed can be dangerous. The fermentation process could build up enough pressure to make the bottle explode. Put the bottle in the fridge once it feels hard when you try to squeeze it.

This process will lead to a minuscule amount of alcohol in the resulting drink. If you do not keep the fermentation going for too long, this should be neglectable.