Before delving into the answer, some initial data: soft drinks are made up of a mixture of water, gas (in this case carbon dioxide, CO2) and some kind of syrup, which gives the drink its color and taste. But these three things are not combined at once – first, manufacturers combine water and gas in a device called a carbonizer. When these two ingredients mix, the water dissolves the CO2, giving rise to a third substance, carbonic acid, which has a liquid form. Then the syrup is added to that acid. The last step is to insert an extra dose of CO2 inside the packaging to increase the internal pressure and preserve the drink. That’s it: here’s the soda.
You may have already noticed that, when the bottle is closed, the mixture is a homogeneous liquid, without gas bubbles. But everything changes when you take the lid off: first, you hear that “tssssssssss” – the noise of extra CO2 escaping. Then the bubbles start to appear. This happens because the pressure in the liquid decreases and slowly the carbonic acid starts to turn back into a gas and escape from the liquid in the form of bubbles.
Now that you know the process, you might be wondering: isn’t there an easier way to make soda? There is, yes: you can mix the syrup directly into natural carbonated water, but this raw material is not as abundant as ordinary water. Therefore, it is cheaper for bottlers to mix water and gas artificially. They have been using this process for more than a century, when the first soft drinks were created. The only difference is that today there are two ways to combine the ingredients: the first is the so-called pre-mix (syrup and sparkling water are combined shortly before the liquid is bottled), used in cans and bottles. The other is the post-mix (the mixture is made at the time of sale), used in snack bars’ soda machines.
portable factory
Snack bar machines mix the drink ingredients on the spot
1. In soda machines, the beverage ingredients are stored at the point of sale: metal cylinders keep the syrups (in our example, there are four different flavors), a plug holds the carbon dioxide (CO2) and the water comes from some filtered source. In the following steps, these three items will be mixed inside the machine.
2. The composition starts with the mixture of carbon dioxide and water. The CO2 and water tanks are connected to a carbonizer, which compresses and dissolves the gas in the liquid, forming carbonic acid — nothing more than carbonated water. Through a tube, the liquid goes to a serpentine, which cools the beverage to the consumption temperature, from 4ºC to 8ºC
3. It is only at the machine exit, at the very end of the process, that syrup and carbonated water come together to form the soda. The two hoses meet and are mixed during the fall itself, in the nozzle. The amount of syrup depends on the setting of the machine — you can enhance or tone down the flavor. Therefore, it is very difficult for machine soda to taste the same as bottled
4. Outside the machine, the carbonic acid begins to separate from the water in the form of CO2 bubbles. The process is very slow and can take hours. Therefore, we get the impression that there is a lot of gas and syrup in the soda – but, in fact, they correspond to only 1% of the mixture! The remaining 99% is just water.