To keep a bottle of soda fizzy, it is generally better to leave the air in the bottle rather than squeezing it out and resealing it. Here's why:
Pressure: The carbonation in soda is a result of dissolved carbon dioxide (CO2) under pressure. When you open the bottle, the release of pressure allows some of the CO2 to escape, leading to the loss of fizziness. By leaving the air in the bottle, you are maintaining a higher pressure environment, which helps retain more of the dissolved CO2 and keep the soda fizzy for a longer time.
Oxygen Exposure: Squeezing the air out of the bottle and resealing it may create a partial vacuum inside the bottle. This can potentially lead to air from the surroundings being drawn into the bottle when the cap is opened again. Oxygen exposure can affect the taste and freshness of the soda, causing it to go flat faster. Leaving the air in the bottle reduces the likelihood of oxygen entering when you open it, helping to preserve the carbonation.
Repeated Pressurization: Squeezing the air out and resealing the bottle repeatedly can subject the bottle to additional stress and strain. This could potentially weaken the bottle or the seal over time, increasing the risk of leaks and loss of carbonation. It is generally more reliable to keep the original seal intact and not manipulate the pressure inside the bottle unnecessarily.
In summary, leaving the air in the bottle helps maintain a higher pressure environment, preserves the dissolved CO2, reduces the exposure to oxygen, and minimizes the risk of damaging the bottle or its seal.