By Nik, founder of 東歐嚴選｜kefir.link and former chef · Updated 2 November 2026
When you strain milk kefir into soft cheese, a pale, sour liquid collects in the bowl, and it is far too useful to pour away. That whey still carries the kefir's live cultures, and a small glass of it turns sweetened lemon water into a tart homemade lemonade. After a few days on the counter the drink tastes less sweet, gains a mild tang and, when the fermentation is lively, a natural fizz.
The leftover that does the brewing
Fresh kefir whey contains a mix of the yeasts and bacteria from the kefir, and those cultures feed on the sugar and slowly ferment the lemonade. That is why the whey has to be fresh and alive: heat can kill the cultures, so whey from a heated cheese will not start anything. Whey protein powder will not work either, because drying destroys the cultures and the powder is mostly extracted protein. Whey drinks are not only a home-kitchen idea. In Switzerland, a whey-based soft drink has been made since the 1950s, and dairy cooperatives backed it because it gave their surplus whey a use.
Let the bottle, not the calendar, tell you
Fermentation produces acids and gas, and its pace depends on temperature, the microorganisms at work and how much sugar is in the liquid. A warm kitchen can make the lemonade fizzy in two days, while in a cool one it may stay almost flat. Chill it after three days either way, because a longer wait at room temperature only adds risk, not bubbles. Fresh, active whey and a bottle that seals tightly both help the bubbles build. As the cultures eat the sugar, the drink keeps the taste of the citrus but becomes less sweet, with a gentle sourness that makes it refreshing over ice.
Orange, honey and other twists
For an orange version, double the juice to about 120 ml and use less water. If the finished drink tastes too tart, a spoonful of honey softens it, and the same method works with other juices or with tea. For a quick drink with no fermenting at all, mix whey with juice or sparkling water, or stir it into butterfly pea tea with honey and a few drops of lemon, which turns the blue tea purple.
Kefir-whey lemonade soda
Ingredients
- 700 ml drinking water Use spring or lightly filtered drinking water. This total includes the water for dissolving the sugar.
- 4 tbsp golden cane sugar Measure with level tablespoons; white cane sugar also works.
- 60 ml lemon juice Freshly squeezed; Taiwanese lemons work well.
- 120 ml kefir whey Fresh, 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.
Comments
No comments yet.
Comments could not be loaded.
Join the discussion
or