Natural carbonation is the process by which carbon dioxide (CO2) dissolves into a liquid through biological or geological activity, rather than being mechanically injected. It happens in two main ways: living organisms like yeast produce CO2 as they consume sugar, or underground water absorbs CO2 from volcanic and geothermal sources deep in the earth. The fizz in champagne, kombucha, and naturally sparkling mineral water all comes from natural carbonation, though the mechanisms behind each are quite different.
How Yeast Creates Carbonation
The most common form of natural carbonation starts with fermentation. Yeast cells consume sugar and break it down into two byproducts: ethanol (alcohol) and carbon dioxide. More precisely, yeast converts glucose into a chemical intermediate called pyruvate, which then splits into ethanol and CO2. This is the same basic process behind bread rising, beer brewing, and winemaking. When fermentation happens inside a sealed container, the CO2 has nowhere to escape, so it dissolves into the liquid under pressure and creates carbonation.
The amount of fizz depends directly on how much sugar the yeast has to work with. In sparkling wine production, roughly 4 to 4.3 grams of sugar per liter produces one “atmosphere” of CO2 pressure. A typical champagne-style wine needs about 25 grams of sugar per liter to reach the 5 to 6 atmospheres of pressure that give it its aggressive, fine-bubbled fizz. Lighter sparkling styles use less sugar: a pétillant (lightly sparkling) wine sits around 2 to 2.5 atmospheres, while a crémant reaches about 3.5 atmospheres with 15 to 18 grams of sugar per liter.
How the Earth Creates Sparkling Water
Not all natural carbonation involves living organisms. Some mineral waters emerge from the ground already fizzy, pressurized with dissolved CO2 from deep geological sources. This happens in areas with volcanic or seismic activity, where carbon dioxide rises from magma chambers or from carbonate rocks melting along tectonic subduction zones. The gas migrates upward through cracks in rock, dissolving into underground aquifers under high pressure. When that water reaches the surface through a spring or well, it arrives naturally carbonated.
These geological CO2 sources are concentrated in seismically active regions. Central Italy, for example, has high CO2 emissions linked to a subduction zone beneath the region, where gas accumulates in the lower crust and builds up pressure. Famous naturally sparkling waters like San Pellegrino and Gerolsteiner come from these kinds of geological settings. Under U.S. labeling rules, water can be called “sparkling bottled water” if, after any treatment, it contains the same amount of CO2 it had when it emerged from its source. The CO2 can be captured and reinjected during processing, but the total amount must match what nature provided.
Natural Carbonation in Beer and Kombucha
Homebrewers and craft breweries often use a technique called bottle conditioning to naturally carbonate beer. After the main fermentation is complete, a small measured amount of sugar (called priming sugar) is added to the finished beer before it’s sealed in bottles or casks. The residual yeast still present in the beer ferments this added sugar, producing just enough CO2 to carbonate the beer inside the sealed container. Common priming sugars include table sugar (sucrose), corn sugar (dextrose), and dry malt extract, each contributing slightly different flavors and carbonation levels.
Kombucha follows a similar two-stage approach. During the first fermentation, a symbiotic culture of bacteria and yeast breaks down sweetened tea over the course of a week or more. The second fermentation is where carbonation builds. The kombucha is bottled in sealed containers, sometimes with a bit of added fruit or sugar to feed the remaining microbes. This secondary fermentation works best at temperatures between 75°F and 84°F. Timing matters: too short and you get flat kombucha, too long and the pressure can build enough to make bottles overflow when opened. Most brewers check progress by carefully cracking a bottle every day or two to gauge how much pressure has developed.
How It Differs From Forced Carbonation
Forced carbonation is the industrial alternative. Instead of relying on biology or geology, manufacturers pump pressurized CO2 gas directly into a liquid. This is how most sodas, commercial seltzers, and many mass-produced beers get their fizz. The process is fast (minutes to hours, compared to days or weeks for fermentation) and highly controllable, allowing producers to hit exact carbonation levels every time.
The CO2 molecule is identical regardless of how it gets into your drink. But the way it integrates into the liquid can affect the drinking experience. Naturally carbonated beverages often develop their fizz slowly under relatively low, self-generated pressure, which tends to produce smaller, finer bubbles. Forced carbonation pushes CO2 into solution quickly under higher external pressure, which can result in larger, more aggressive bubbles that leave solution faster. Think of the difference between the delicate, persistent fizz of champagne and the rapid, coarse bubbles of a freshly opened can of soda. The distinction isn’t absolute, since forced carbonation can be tuned to produce fine bubbles, but many brewers and winemakers report a smoother, more integrated mouthfeel from natural carbonation.
Bubble size also affects how you perceive the drink on your tongue. Smaller bubbles create a gentler, almost creamy sensation, while larger bubbles feel sharper and more prickly. This is part of why naturally carbonated sparkling wines and bottle-conditioned beers are often described as having a softer, more refined texture compared to their force-carbonated equivalents.
Why Natural Carbonation Takes Longer
The tradeoff for that smoother fizz is time and unpredictability. In the traditional champagne method (méthode champenoise), bottles undergo secondary fermentation and then age on their spent yeast for months or even years. Bottle-conditioned beer typically needs one to three weeks after bottling before the carbonation is fully developed. Kombucha’s secondary fermentation runs two to five days depending on temperature and sugar content.
Temperature, sugar concentration, yeast health, and even altitude all influence the final result. Too little sugar produces flat drinks. Too much can generate dangerous pressure inside glass bottles. Yeast that’s too cold goes dormant and stops producing CO2. Yeast that’s too warm can produce off-flavors alongside the carbonation. This variability is why forced carbonation dominates commercial beverage production: consistency at scale is easier when you control the gas input directly rather than relying on billions of microorganisms to do their job correctly.
For producers willing to invest the time, though, natural carbonation adds complexity that goes beyond the bubbles themselves. The yeast activity during secondary fermentation generates subtle flavor compounds, and the extended contact between the liquid and spent yeast cells (called lees) can add depth, particularly in sparkling wines. It’s a slower, less predictable process, but for many drinkers, the result is worth the wait.