Citric acid

Citric acid gives citrus fruits – oranges, lemons and limes – their bitter taste. The taste receptors on your tongue detect ‘sour’ when they pick up hydronium ions (H₃O⁺), formed when H⁺ ions react with water. Citric acid has four available H⁺ ions. This bitter taste means citric acid is used as an additive in soft drinks. As well as improving the flavour, citric acid (mixed with its salt, sodium citrate) also acts as a buffer, helping to control the pH. And because it is soluble, this magnificent molecule will even dissolve in concentrated syrups.