Wash 400 g of fresh strawberries thoroughly, preferably untreated or organic strawberries, to remove visible dirt while preserving as much natural fruit yeast as possible.

Place the washed strawberries in a clean, sterilized large glass jar. Pour in 1 L of filtered non-chlorinated water.

Add 70 g of unrefined cane sugar to the jar. Stir well with a clean wooden spoon until the sugar is mostly dissolved.

Cover the jar with a clean cloth or paper towel. Secure the cover with a rubber band so air can circulate while debris stays out.

Leave the covered jar at room temperature, ideally 20 to 25°C, for 2 to 4 days. Keep it away from direct sunlight.

Stir the mixture with a clean wooden spoon 2 to 3 times daily during fermentation. Watch for small bubbles on the surface and a pleasant fruity, lightly fermented aroma.

Once the drink is lightly sparkling and fruity, strain out the strawberry solids through a fine mesh strainer. Collect the liquid in the swing-top glass bottle.

Seal the swing-top glass bottle and leave it at room temperature for 1 to 2 days to build carbonation. Open the bottle carefully once every day to release excess gas.

Refrigerate the strawberry soda once it reaches the desired carbonation. Serve chilled and open carefully because the naturally fermented drink may be fizzy.