Food: Citric acid C₆H₈O₇ (can be found in Citrus fruits such as lemons and limes), Acetic acid CH₃COOH (can be found in vinegar, present in small amounts contributing to the tartness of fruits such as apples) Lactic acid C3H6O3 (found in milk and produced by the fermentation of dairy products like yoghurt ), Tartaric acid C4H6O6 (most abundant in grapes, can be found in cherries, strawberries, peach, pear), Malic acid C4H6O5 (occurs naturally in fruits such as apples and cherries) , Fizzy drinks (contain carbonic acid H₂CO₃)