Rhubarb is a unique vegetable because it tastes very sour. This is because it has a lot of malic and oxalic acids.
Tart cherries, or Prunus cerasus L., are small, bright red stone fruits with a sour taste.
Gooseberries are small, round fruits that can be different colours and can taste sweet or very sour.
Raw cranberries taste sharp and sour because they don't have much sugar and have a lot of organic acids, like citric and malic acids.
Vinegar is a liquid made by turning the sugars in a carbohydrate source, like a grain or fruit, into alcohol.
Fermented veggies and spices are the basis for the classic Korean side dish known as kimchi.
Live bacteria in milk ferment yogurt, a popular dairy product. Lactic acid is produced when bacteria break down milk sugars, giving yoghurt a sour taste and smell.
Because kefir grains can have up to 61 strains of bacteria and yeasts, it is thought to be a better source of probiotics than yogurt.