Can lemon sodas go bad?
Acidity regulator E330 is citric acid. I found no indication that it's chemically instable at temperatures &lt; 100°C and a study found it stable over a period of 5 months.

Additive E211 is sodium benzoate that's used to stop bacterial and fungal growth in acidic foods and drinks. A study found that over a period of 90 days 4 - 8% of sodium benzoate degrades. I'm no chemist and don't know what chemicals the result of this degradation are, but they could influence the taste of the soda and loose the ability to stop bacteria growth.

Another study found that in peach puree treated with sodium benzoate, the amount of sucrose (common sugar) decreased and the amount of glucose and fructose increased. Although all 3 are different types of sugars, there is a notable difference in taste.

Additive E202 is potassium sorbate, another food preservative and probably the culprit for the yellow color. Food Reviews International writes:


  However, in solutions and in foods, [potassium sorbate] undergoes autoxidation during storage, forming carbonyls and other compounds. Many factors (e.g., pH, temperature, packaging, water activity, and composition of food) influence its stability. Degradation of sorbic acid is associated with development of browning in foods. Acetaldehyde and /3‐carboxylacrolein have been reported to be the major degradation products of sorbic acid in aqueous solutions. β‐Carboxylacrolein is found to be responsible for sorbate‐induced browning in foods as it reacts with amino acids and proteins to form brown pigments.


Plastic bottles are known to let the carbonation of carbonated water escape over a long time. Carbonation means that carbonic acid is solved in water, which then forms little bubbles of carbon dioxite (CO2). As long as the carbonic acid is still dissolved in the soda, it adds a slightly tart flavor to it, which we are used to. Once most of it evaporated, the overall flavor of the soda changes to that of a stale soda (which it basicly is).

As to the "natural flavor", since it's not named, we cannot know for sure what it was. But there's a good chance that it also degenerated at least partially over time.

So, to answer your question: Yes, lemon sodas can go bad. That's why there is a "best before" date printed on them. As far as I understand the chemistry involved, your soda wasn't poisenous, but it was chemically altered enough to be considered "gone bad".