You open a bottle. You hear the familiar hiss of gas. You take a sip of a refreshing, slightly tart drink with the aroma of fresh raspberry or ripe peach — and you know exactly what's inside, because you made it yourself.
It's not kombucha. It's not kefir. It's nothing from a store shelf. This is something you prepare with live lactic acid cultures, fresh fruit juice, and a little patience. The result is a naturally carbonated, non-alcoholic drink rich in beneficial metabolites. With certain fruit combinations, it approaches what science today calls a postbiotic drink.
We'll show you how.
What happens in the bottle?
When you add the Onbiome starter culture to sweetened fruit juice, the live lactic acid cultures begin to feed — primarily on the inulin (prebiotic) and the sugars in the juice. As a result of this metabolic process, natural CO₂ is released, carbonating the drink without any artificial additives.
At the same time, valuable metabolites accumulate in the liquid — the by-products of fermentation that make the drink not only delicious but also functional.
Important to know: every fruit or extract differs in composition and enzymatic activity. That's why this recipe doesn't give exact numbers for every step — it gives principles and indicators that will teach you to observe and feel the process. This is the most valuable skill in home fermentation.
What you need
Ingredients:
- Fresh fruit juice or herbal extract
- Clean spring water
- Inulin — about 8g per liter of liquid
- Sweetener of choice: sugar, honey, maple syrup
- Onbiome starter culture for soy yogurt — 1 capsule per liter of liquid
- Optional: natural essence or flavor (ginger, mint, vanilla...)
Equipment:
- 5 or 10-liter plastic bottle (from mineral water)
- 0.5-liter plastic bottles for bottling — essential for high pressure
- Disinfecting alcohol for cleaning vessels
No special equipment. No laboratory. Just attention and observation.
Step by step
Step 1 — Preparing the juice
Use fresh homemade juice from healthy, well-washed and peeled fruit. Before juicing, remove seeds, pits, and peel — they worsen the taste and aroma of the finished drink, and the peel of many fruits contains substances that interfere with fermentation. The goal is clean, clear juice without large pulp.
If you don't have fresh fruit, you can also work with sterilised syrups with low sugar content. For herbs (mint, sage, elderflower, fig leaves), prepare a concentrated cold or warm extract.
Example with lemonade: Juice lemons, strain the juice, remove the seeds. You get clean lemon juice, ready for the next step.
Step 2 — Dilution with water
Dilute the juice with clean spring water to taste. Guide: juice-to-water ratio of 1:1 to 1:3, depending on the intensity of the fruit. There's no wrong answer here — the indicator is your taste.
Step 3 — Inulin, sweetener, and flavors
Add inulin — approximately 8 g per litre. For juices rich in natural fibre (fig, raspberry), you can reduce slightly. For more watery fruits — stay close to the recommended dose.
Stir until fully dissolved, then adjust sweetness. The goal is approximately 6–8% sugar content — the solution should taste sweet, not sour. Acidity develops later, during fermentation.
Now is the moment for essences or flavourings. A few classic combinations:
- Lemon + ginger
- Raspberry + mint
- Peach + vanilla
- Fig + mint
Step 4 — Adding the starter culture
All previous steps are best carried out directly in the large plastic bottle — it is naturally clean and easy to disinfect with a little alcohol.
Add the contents of 1 capsule of Onbiome starter culture for soy yogurt per litre of liquid. Important: use this specific starter — the Bulgarian yogurt starter has a different microbial composition and will not successfully ferment a fruit solution.
For more concentrated solutions, you can reduce to 1 capsule per 1.5–2 litres, but for a first attempt we recommend the standard ratio — this ensures a predictable result.
Step 5 — First fermentation (room temperature)
Seal the bottle tightly and leave it at room temperature, in the dark, for 2 to 3 days. Fill to approximately 80% of the volume — leave an air chamber for the accumulating CO₂.
Morning and evening, shake the bottle without opening it. Do not loosen the cap: the cultures are anaerobic and work without air access.
How do you know it's ready? The bottle will become hard. This is your indicator — not the clock, but the bottle itself. That's why we work with plastic: the pressure can rise significantly, and a glass bottle carries a risk of breaking.
Step 6 — Bottling and second fermentation (in the refrigerator)
When the bottle is hard, transfer the drink into small 0.5 L plastic bottles. Fill to the top, tighten the caps firmly, and place in the refrigerator.
The second fermentation lasts approximately one week. The indicator is the same — the bottles will gradually harden. When they are firm and stable, the drink is ready.
If the bottles don't harden
If after fermentation the bottles remain soft, something in the process did not go correctly. Check the liquid — if it is cloudy with a slimy sediment, do not consume it. With clean fermentation, the sediment is fine and mixes easily when shaken.
Storage and opening safety
The finished drink is stored in the refrigerator and keeps for months — the live cultures work slowly at low temperature, and the acidic environment is a natural preservative.
When opening, be careful — the pressure inside is significant! Unscrew the cap slowly and gradually, without removing it all at once, and keep the bottle away from your face.
Example combinations
| Base | Flavor | Sweetener | Character | Note |
|---|---|---|---|---|
| Lemon | Ginger | Honey | Invigorating, refreshing | Classic — ideal for beginners |
| Orange | — | Honey or sugar | Soft, slightly sweet | Fast and predictable fermentation |
| Raspberry | Mint | Sugar or honey | Fruity, fresh | Intense color and aroma |
| Peach | Vanilla | Honey | Soft, dessert-like | Delicate fermentation |
| Apple | — | Sugar or honey | Neutral, versatile | Good base for experiments |
| Elderflower (extract) | — | Honey | Floral, aromatic | Prepare a strong extract |
| Mulberry | — | Honey or sugar | Rich, slightly tart | Shared by Onbiome customers |
| Fig leaf (extract) | — | Honey | Exotic, unusual | For the curious and advanced |
⚠️ Pear is a fruit where fermentation may not proceed successfully. If you decide to try it, pay extra attention to hygiene and watch for signs of failed fermentation.
Finally
A homemade fermented drink is alive — and that is precisely its value. Every batch is slightly different, every fruit combination holds surprises. Over time you will learn to read the bottle, sense the aroma, and know when the right moment has come.
The Onbiome starter culture is your starting point — everything else is your curiosity.
