Getting fizz into water comes down to one idea: push carbon dioxide gas against the water hard enough, and more of it dissolves than the water would hold at normal air pressure. Every method, from a 1700s brewery experiment to a countertop machine, is a way of applying that pressure. The gas doesn’t just hide in the water, either. A small share reacts with it, which is why carbonated water tastes faintly sharp rather than plain.1Chemistry LibreTexts. 13.2: Phase Changes
Pressure and Cold Are What Push the Gas In
Carbon dioxide dissolves in water far more readily than gases like oxygen or nitrogen, which is why it is the gas used for fizz.2World Ocean Review. When carbonate formation loses equilibrium The amount that dissolves rises in step with the pressure of the gas above the water. Doubling the gas pressure roughly doubles how much CO2 the water can take up. Sealing water in a container with high-pressure CO2 therefore loads it with far more gas than open air ever could.
Inside a sealed bottle, dissolved gas and the gas above it sit in a balance: molecules keep entering the water and leaving it at the same rate while the cap is on. Opening the cap drops the pressure to normal air pressure. The water now holds more CO2 than it can keep, so the extra slowly leaves. That is why a closed bottle stays fizzy for months and an open one goes flat in hours.
Temperature changes how much the water can keep. Cold water holds noticeably more dissolved CO2 than warm water,3Journal of Physical and Chemical Reference Data. The Solubility of Carbon Dioxide in Water at Low Pressure so commercial carbonators chill water to about 4°C before adding the gas.4Chemistry and Technology of Soft Drinks and Fruit Juices. Carbonated beverages In a sealed bottle, warming raises the gas pressure inside sharply, because CO2 is pushed out of the liquid into the space above it.5PubMed. Carbon Dioxide in Bottled Carbonated Waters and Subsequent Bubble Nucleation under Standard Tasting Condition A warm bottle sprays more when opened.
Dissolved salts lower how much CO2 water can hold.6Reaktoro. Carbon-dioxide solubility in brines with different salinity and temperature Table salt has a bigger effect than potassium chloride.7Journal of Supercritical Fluids. Solubility of CO2 in aqueous solutions of NaCl, KCl, CaCl2 and their mixed salts at different temperatures and pressures
How a Home Soda Maker Does It
A home soda maker stores carbon dioxide in a cylinder under high pressure.8SodaStream. How Is Water Carbonated? Pressing the button opens a valve and sends gas into the sealed bottle of water.9Advanced Mixology. How Does SodaStream Work? Carbonation & Mechanism Explained The pressure inside the bottle spikes and CO2 is forced into the water. Excess pressure is vented with a hiss when you release the button or unscrew the bottle.
Each press does a slightly different job. The first fills the space above the water with gas. The water absorbs some, the pressure drops a little, and the next press tops it up. Several short presses give more fizz than one long one.
The machine uses a cylinder rather than the air around you because air is only a tiny fraction CO2, so squeezing room air into water would add very little of the gas you want. The cylinder holds nearly pure CO2, kept compressed so a large amount fits in a small canister. Each press releases only a small portion, so one cylinder can carbonate many bottles.
Chill the water first, ideally in the fridge, because cold water absorbs more CO2.10Chemistry and Technology of Soft Drinks and Fruit Juices. Carbonated beverages Add flavor syrups after carbonating, not before, since sugar and particles cause foaming over. For the same reason, carbonating juice or wine can foam out and clog the machine. Overfilling the bottle leaves too little space for gas, and leaving the bottle open lets what you added escape quickly.
Factories do the same thing on a larger scale. They mix chilled water and gas continuously under pressure, and bottles are sealed while still pressurized. Commercial sparkling waters contain roughly 3 to 7 grams of CO2 per liter.11PubMed. Carbon Dioxide in Bottled Carbonated Waters and Subsequent Bubble Nucleation under Standard Tasting Condition
What the Gas Does to the Water
A small share of the dissolved CO2 reacts with water to form carbonic acid, a weak acid.12Chemistry LibreTexts. 13.2: Phase Changes That acid partly breaks apart into hydrogen ions and bicarbonate, the same substance in baking soda.13Chemistry LibreTexts. 13.2: Phase Changes Some of it goes a step further to carbonate ions.14World Ocean Review. When carbonate formation loses equilibrium The result is mildly acidic water, which gives its sharp, slightly sour bite. Only a small share becomes acid because the reaction runs both ways, and at any moment most of the gas is still just dissolved CO2.
As the drink goes flat, CO2 leaves the water and the reaction runs in reverse, so the weak acid turns back into CO2 and water. With less acid left, the pH rises back toward that of the original water, and flat sparkling water tastes much like plain water again. Flat soda can taste sweeter because the acid bite is gone, and cold drinks can taste sharper partly because they hold more dissolved gas.
The reaction also matters for metal. Dry CO2 doesn’t harm metal, but once it forms the weak acid in water it can corrode metals.15PubMed Central. Mechanism and anti-corrosion measures of carbon dioxide corrosion in CCUS: A review Carbonated water should be stored in glass, plastic, or lined cans rather than bare metal.
Why the Bubbles Form Where They Do
Bubbles don’t form randomly; they start at tiny trapped gas pockets.16PubMed. Carbon Dioxide in Bottled Carbonated Waters and Subsequent Bubble Nucleation under Standard Tasting Condition Many of these are microscopic cellulose fibers from towels stuck on the glass.17PubMed. Modeling the kinetics of bubble nucleation in champagne and carbonated beverages Dissolved CO2 drifts into the pocket until the bubble grows big enough to break free and rise.18Journal of Food Engineering. Bubble dynamics in various commercial sparkling bottled waters A perfectly clean, smooth glass shows fewer bubbles.
Below a certain level of dissolved CO2, bubbles can’t form at all.19PubMed. Carbon Dioxide in Bottled Carbonated Waters and Subsequent Bubble Nucleation under Standard Tasting Condition That minimum is lower in warmer water and with bigger gas pockets.20PubMed. Carbon Dioxide in Bottled Carbonated Waters and Subsequent Bubble Nucleation under Standard Tasting Condition Flat-looking water can still hold some gas, which a warm glass or a stir may release.
Dropping in salt, ice, or a candy adds many new bubble starting points. Each one releases gas at once, which is the trick behind cola fountains, and it speeds the drink going flat.
To keep a drink fizzy longer, pour down the side of a tilted glass, keep the bottle cold and tightly capped, and avoid shaking an opened bottle.
Carbon Dioxide Added to Tap Water and Wastewater
Some cities soften hard water with lime, which leaves it too alkaline and prone to building scale in pipes.21National Drinking Water Clearinghouse Fact Sheet. Lime Softening So plants bubble in carbon dioxide to lower the pH.22National Drinking Water Clearinghouse Fact Sheet. Lime Softening The CO2 converts carbonate into bicarbonate, which stops calcium deposits.23Florida Water Resources Journal. Lime Softening—the Forgotten Technology: Optimization Case Studies From South Florida The gas comes from on-site burning or from liquid CO2 tanks.24National Drinking Water Clearinghouse Fact Sheet. Lime Softening
Industries use CO2 instead of strong acids to neutralize alkaline wastewater.25Sustainability. Carbon Dioxide-Based Neutralization of High-Density Sludge Effluents as a Sustainable Climate and Water Quality Alternative to the Use of Strong Mineral Acids It can bring very alkaline water from pH 10 down to near neutral within minutes.26Sustainability. Carbon Dioxide-Based Neutralization of High-Density Sludge Effluents as a Sustainable Climate and Water Quality Alternative to the Use of Strong Mineral Acids Breweries can reuse CO2 from their own processes instead of buying sulfuric acid.27PubMed. pH regulation of alkaline wastewater with carbon dioxide: a case study of treatment of brewery wastewater in UASB reactor coupled with absorber
CO2 is a safer choice than strong acid here. It is a weak acid, so overshooting to a dangerously low pH is hard. It is easier to store and handle, and it avoids adding sulfates or chlorides to the water.
How Nature Carbonates Water
Oceans absorb CO2 from the air, and rising levels from fossil fuels are making seawater more acidic.28Annual Reviews. Ocean acidification: the other CO2 problem Gas moves across the sea surface in both directions, and the net flow goes into the water when the air holds more CO2 than the water is balanced with. Cold water absorbs more, so cold regions take up a lot. Currents carry the dissolved gas downward, making room at the surface to absorb more.
Naturally sparkling mineral springs get their fizz from volcanic CO2 dissolving in groundwater under pressure. In Cameroon’s Lake Nyos, CO2 seeping in from below built up in deep water until it burst out in 1986.29Journal of Volcanology and Geothermal Research. A trigger mechanism for the Lake Nyos disaster
People worked out how to copy this in the 1700s. Joseph Priestley dissolved CO2 into water over a brewery vat in 1767, and Jacob Schweppe later used a pump to dissolve it under pressure, starting a business in 1783. His pressure method is the ancestor of today’s machines.