Almost every bottled soft drink is noticeably acidic, including ones that taste primarily of sugar. That acidity is doing preservation work before it does anything for flavour.
Acidity is the first line of preservation
Most spoilage organisms grow poorly below a certain acidity, and drinks formulated under that threshold can be made shelf-stable with relatively gentle heat treatment.
A less acidic drink has to be sterilised far more aggressively, which cooks the flavour and changes the colour, or else kept refrigerated throughout distribution.
Given the choice between a harsher process and a tarter recipe, manufacturers have consistently chosen the tarter recipe.
Sugar and acid are set against each other
A drink with the sugar level of a typical soft drink and no acid tastes cloying and sits heavily on the palate.
Acid cuts that perception, so the same sugar concentration reads as refreshing rather than syrupy. The two are tuned together as a ratio rather than set independently.
This is why reduced-sugar versions often taste sour: removing sugar without rebalancing the acid exposes what was always there.
Colour and aroma survive better in acid
Many natural pigments, particularly the reds and purples from fruit, hold their colour in acidic conditions and shift or fade as acidity drops.
Some aroma compounds are similarly more stable at higher acidity, so a bottle keeps tasting like itself further into its shelf life.
A drink that looks the same after months on a warm shelf is usually acidic enough to be defending its own appearance.
Carbonation contributes acidity of its own
Dissolved carbon dioxide forms a weak acid in water, so a carbonated drink is measurably more acidic than the same recipe flat.
That contributes to the bite people attribute to bubbles, which is partly a chemical sensation rather than a purely physical one.
It also means a drink loses some of its perceived sharpness as it goes flat, which is why stale soda tastes sweeter rather than merely duller.
Low-acid drinks need a different playbook
Dairy-based and plant-milk drinks cannot be acidified without curdling, so they are processed at high temperature under pressure or sterilised and filled aseptically.
That equipment is expensive and the resulting product often carries a cooked note that formulators then have to mask.
The split explains the layout of a chilled aisle: acidic drinks sit on ambient shelves, low-acid ones need either refrigeration or serious processing behind them.