700mldrinking waterUse spring or lightly filtered drinking water. This total includes the water for dissolving the sugar.
4tbspgolden cane sugarMeasure with level tablespoons; white cane sugar also works.
60mllemon juiceFreshly squeezed; Taiwanese lemons work well.
120mlkefir wheyFresh, refrigerated plain kefir whey with live cultures, bought or strained from plain milk kefir, and never heated. Whey protein powder will not work.
You will need
Heatproof mixing jug
Measuring jug and measuring spoons
Mixing spoon
Citrus juicer
Fine-mesh strainer
Funnel
Food-grade bottle rated for carbonation, with a secure cap
Instructions
Wash and sanitize the bottle and any utensils that will touch the drink. Follow the equipment or food-contact sanitizer instructions.
Measure 60 ml of freshly squeezed lemon juice after straining out the seeds and coarse pulp.
In the heatproof jug, dissolve the sugar in a little warm water taken from the measured 700 ml.
Stir in the remaining water and lemon juice.
Let the lemon mixture cool to room temperature.
Stir the kefir whey into the cooled lemon mixture.
Using a funnel, fill the pressure-rated bottle, leaving at least 2.5 cm between the liquid and the opening. Seal the bottle.
Let the bottle ferment out of direct sunlight at about 21–27°C (70–80°F) for about 2–3 days. Start checking on the first day, following the next step; active whey may produce bubbles sooner.
Once or twice a day, hold the bottle over the sink and slowly loosen the cap to release gas, then reseal. Do not shake it or point the opening toward anyone. If foam rises quickly, close the bottle and refrigerate until thoroughly cold before opening again.
Refrigerate after 2–3 days, or sooner if the drink becomes fizzy and tart. When thoroughly cold, open slowly over the sink and pour to serve.
Use a bottle made for carbonated drinks. Fermentation pressure can break ordinary storage jars or decorative bottles.
Some kefir cultures produce little fizz. Do not extend the room-temperature fermentation beyond the stated time just to get more bubbles.
Fermentation can produce alcohol; the amount is unknown without testing. Children, pregnant people and anyone avoiding alcohol should choose another drink.
Storage and safety
Keep at 4°C (40°F) or below and drink within 1–2 weeks. Slowly release pressure daily, as fermentation continues in the fridge. Discard the entire batch without tasting if you see mold or notice a rotten smell or unusual sliminess. Contains milk.