Editor's note: To read part one of this article, which was originally published in the September 2013 issue of Water Technology, please visit WaterTechOnline.com.
When CO2 gasses off from a carbonated fountain beverage, it carries the syrup scent with it, which intensifies the aroma and also the taste. The carbonic acid, a byproduct of CO2, also gives the drink its “bite” (not the CO2 bubbles as some think). The flavor recipe of syrup is designed with acids, such as citric, to create a certain taste profile and carbonic acid is calculated into this recipe.
When water enters the carbonator, CO2 under pressure is literally forced into the water. At this point most of the CO2 is trapped by the increased pressure and intermolecular forces between the water molecules. Some molecules of CO2 react with the water to produce carbonic acid (H2CO3).
The greatest factors influencing the ability to carbonate water for beverage production will be temperature and pH. All gasses are more soluble in cold liquids versus hot. The colder the liquid, the less likely the gas will gas off from solution.
The second most important factor will be pH. Introducing CO2 into water creates a very dynamic complexity. In a carbonator, the water is in the lower region of the tank and CO2 is in the upper region. Water is sprayed into the CO2 under pressure and this drives the gas into the liquid. Some of this CO2 gas will be forced between the water molecules and some of the CO2 will convert into carbonic acid.
In its natural state, water likes to have a balance between bases and acids. The problem is, the environment of a water boost is very unnatural as CO2 is being introduced into the liquid water under pressure. If the water is high in alkalinity (high alkalinity is usually associated with high hardness, such as calcium and magnesium ions), a buffering action occurs that neutralizes the acids. It’s like taking an antacid pill, which is calcium carbonate, to neutralize excessive stomach acid. The alkalinity itself is stable, which means it doesn’t change as this buffering occurs. However, it has a large effect on the acids, which essentially convert to salts (sodium bicarbonates), as shown in Figure 1: