Carbonation in Tonic Water

1. Introduction

Tonic water is carbonated water infused with quinine. This compound which is extracted from the bark of Cinchona tree provides the distinctive bitter taste. For a drink to be called tonic water, a minimum level of quinine must be added. The maximum amount that can be added is also regulated, but it varies from country to country, for instance it is 57 mg/L in the United Kingdom, 83 mg/L in USA, and 85 mg/L in Germany. To mask the bitter flavor, sweeteners such as fructose, as well as artificial flavoring agents are also used in the preparation of tonic water. As tonic water is a moderately carbonated product, the quality of the added carbonated water has a significant impact on the organoleptic properties of the product.

2. Carbonation process

Carbonation is the impregnation of a liquid with carbon dioxide gas. When dissolved in water it forms carbonic acid. These acid in combination with the product produces the acidic and bitter taste found in CSD’s. The carbonation process is the last process while manufacturing tonic water. The dissolved gas not only adds a distinctive taste and a sparkling effect to the beverage, but also acts against bacteria. Soft drinks beverages contain carbonation ranging from 1 to 5 volumes of CO₂ gas per volume of liquid. In tonic water, the level of carbonation is not more than 4 CO₂ gas volumes.

The final premix is fed to a vessel pressurized with CO₂ gas which is judged by the pressure and flow rate of the CO₂, which is critical to ensure the needed carbonation level. Therefore, the greater the surface area of the liquid exposed to the CO­₂, the higher the rate of CO₂ absorption will be in the liquid. For a given volume, the amount of carbon dioxide than can be retained in solution depends on the temperature and pressure. The lower the temperature while filling, the greater the amount of carbon dioxide that is retained.

Typically, water alone is often carbonated to ensure minimum contamination of the system by syrup or concentrates. The product is spread over chilled plates, such that the product runs down the plates as a thin film. This is carried out in a constant-pressure carbon dioxide atmosphere, the lighter, displaced air being bled off. Chilling the product between 1°C to 5°C as a film maximizes the surface area available to the CO₂, thus promoting effective carbonation. This has the added benefit that at a lower temperature the gas stays in solution more easily.

 

Carbonated beverages can be manufactured in one of the following three ways:

1. a) The ingredients of the end product are made up as a syrup that is typically five or six time concentrated. This syrup will often be flash pasteurized and then mixed in proportioning system with the required amount of water, which has been carbonated in a separate operation. The carbonated end product is then filled into the required container. This approach is known as the premix method.

 

1. b) The concentrated syrup is dosed into each container on the filler and the container topped up with carbonated water. After leaving the filler, container will be mechanically inverted to ensure adequate mixing of syrup and carbonated water. This is the post mix method.

 

1. c) A less frequently used method is to make up the product at drinking strength, inject CO_2­ in a suitable system, and then fill the container.

 

3. Functional Parts of a Carbonation system

The production of drink considers deaeration of water for reducing foam in the final drink during the phase bottling and avoid the oxidation of the final product. The mixing between water and syrup to achieve the right dilution of syrup which realizes the final product. The following are the function parts of a carbonation system:

• Deaeration group: It is composed with a horizontal tank kept to a high grade of vacuum by a liquid ring vacuum pump, the incoming water is added of CO₂ and sprayed by means of high efficiency nozzles; a second pump recycles the water from first to second stage where a second CO₂ addition takes place. The system ensures removal of the air inside the feeding water, the addition of CO₂ is manually adjusted with a special needle valve provided with flow meter variable area.
• Dosage group: It allows the automatic dosage control of the right quantity of syrup in the water, the correct amount is ensured thanks a control and measure chain consisting of mass flow meters mounted both on the syrup and water line.
• Cooling group: A plate heat exchanger cools the mixed product down to 6°C. The thermal exchange is obtained in countercurrent with glycol solution regulated by a pneumatic modulating valve. This valve is controlled by a temperature probe mounted on the drink outlet pipe from the heat exchanger.
• CO₂ injection group in line high pressure: It is obtained thanks to the use of a pneumatic modulating valve, a mass flow meter and one injector able to disperse the gas into the liquid.
• Mixing group: It is realized by means of two static mixers with high performance which allow the best mixing of gas into liquid.
• Storage and final product stabilization group: It is a buffer tank kept at a constant pressure by means of a CO₂ injection valve and a vent modulating valve. The tank is equipped with a continuous level to manage the various processing phases and adapt the work range to the filler one. A centrifugal pump regulated by inverter allows the transfer of the final drink up to the filler.

 

4. Filling of carbonated beverages

The filling of carbonated beverages is achieved under gravity, the rate of flow being dependent on the head difference between the filler bowl and the container.

            The rate of flow to fill the container is a function of the overpressure applied to the top of the filling bowl (p), the viscosity of the liquid to be filled (µ), the diameter of the filling tube (d) and the length (d) and the length of pipe (l). This can be expressed mathematically by the following formula:

 

5. Further Reading

• Abu-Reidah, I. Carbonated Beverages, Trends In Non-Alcoholic Beverages
• Ashurst, P. Chemistry and Technology of Soft Drinks and Fruit Juices. Wiley, 2016.
• Robertson, L. Food Packaging and Shelf Life: A Practical Guide.
• Ashurst, P. The Stability and Shelf Life of Fruit Juices and Soft Drinks.