They have acids in them--citric, malic, or tartaric acids. Acids are sour.
malic acid
Plant acids are naturally occurring organic acids such as citric acid and malic acid produced by plants in their fruits and other locations. In fruits the acids give plants a tangy taste.
You can find acids in fruits, for example oranges this contains Citric acid
papaya
Fruits, particularly lemons.
Acids commonly found in smoothies include citric acid from citrus fruits like oranges and lemons, malic acid from fruits like apples, and ascorbic acid (vitamin C) from fruits like strawberries and kiwis. These acids provide a tart and refreshing flavor to the smoothie.
There are naturally occurring sugars and ascorbic acids in fruits that cause this.
"How about 'Fruit Frenzy: Exploring the Effects of Acids on Common Fruits'? It's catchy, straight to the point, and screams 'I know my way around a lab'. Just make sure your project is as juicy as your title, honey."
The main acids in fruits include: malic acid (apples), tartaric acid (grapes), and citric acid (citrus fruits).
Yes, fruits contain acid.
Citric Acid is common in many different types of fruits.