People readily understand that solids can dissolve in a liquid. Salt or sugar dissolve in water and the warmer the water, the faster the rate of dissolution. We learn this in elementary school. But for some reason, the idea that gases can dissolve in water causes more confusion. Indeed, they do dissolve. If oxygen from the air did not dissolve in water, for example, fish could not survive. And if carbon dioxide did not dissolve in water, we wouldn’t have carbonated beverages. Temperature, on the other hand, has a different effect as to how gases and solids dissolve in water.
Heat causes dissolved gases to evaporate from a solution, meaning that gas solubility decreases as the temperature increases. For example, a glass of soda in the fridge will retain carbonation longer than one left at room temperature. Now, for the foaming effect. The amount of gas that dissolves in a liquid depends on how much pressure is applied to force the gas into solution. In the case of champagne, the carbon dioxide gas is generated during the fermentation process and is not allowed to escape. The pressure builds to several atmospheres, so as soon as the cork is removed, the pressure above the liquid drops to one atmosphere. At this pressure, the liquid cannot hold as much dissolved carbon dioxide and the excess now explodes out of the bottle bringing the liquid with it. But why does shaking the bottle make this a more memorable experience?
The usual (and not scientifically accurate) explanation is that shaking the bottle builds up pressure above the liquid, so that when the bottle is opened the extra pressure squeezes the liquid out more quickly. However, this is not so and can be proven by inserting a pressure gauge into a bottle instead of a cork. No increase in pressure happens with shaking! This means that shaking cannot alter the pressure above the liquid, (in this case the champagne), and therefore cannot cause more gas to come out of it. What shaking can do, however, is cause the gas above the solution to mix with the liquid. As the liquid sloshes around, it drags some of the gas above it down below its surface. And since the liquid is already saturated with the gas, no more can dissolve, so instead it forms bubbles. In other words, the gas that occupied the space above the liquid is now distributed throughout the liquid in the form of bubbles. At this point, if the bottle is opened, the pressure above the liquid is reduced and it can no longer hold as much dissolved gas as it did at the higher pressure. The gas will now start to escape from the solution. How quickly it escapes will depend on the surface area of the liquid. Without shaking, the only exposed surface is at the neck of the bottle. But if you shake, bubbles become dispersed through the liquid and the surface area becomes very large, as each bubble now represents a liquid-gas interface. The dissolved carbon dioxide quickly evaporates into each bubble, causing the bubbles to expand, thereby propelling the liquid out of the bottle as a foam.
Shake or no shake, your champagne will taste the same.
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