Why a kiwifruit tastes so tart
Love ‘em or loathe ‘em, the kiwifruit is full of vitamins which the body needs to be happy and healthy. Within its gritty green flesh are two important acids.
The first is Vitamin C or ascorbic acid. Some species of animal can make their own Vitamin C but those that can’t have to include it in their diet. Vitamin C changes shape to help it move it around the body and assist in skin growth and healing. A lack of it causes scurvy which was common in sailors who lived off dry crackers when they were at sea. Luckily Captain Cook noticed that if his crew included fresh fruits in their diet, scurvy could be avoided, allowing those aboard the Endeavor to stay alive long enough to discover New Zealand!
The acid which gives you that lip-curling reaction is Citric Acid a stronger acid than Vitamin C. Sourness is sensed through our taste buds. The more loose hydrogen atoms in the substance, the more sour it tastes because the positively charged atoms create an electrical signal from the tongue to the brain.
Kiwifruit contains many other interesting molecules. Have you ever decorated a pavlova with kiwifruit hours before it has to be served only to find that when it’s time for dessert the pav has become all oozy? This is due to an enzyme in the fruit called actinidin which dissolves the milk proteins in the cream.