Citric acid is a weak organic acid. It is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks. It also serves as an environmentally benign cleaning agent and acts as an antioxidant.
Citric acid exists in a variety of fruits and vegetables, most notably citrus fruits. Lemons, limes and chokeberries have particularly high concentrations of the acid; it can comprise as much as 8% of the dry weight of these fruits.
As a food additive, citric acid is used as a flavouring and preservative in food and beverages, especially soft drinks. It is denoted by E number E330.
In breadmaking the effect of adding ascorbic acid to the flour is to increase the volume of loaf. It helps the yeast to work faster and prolongs its action. Half a vitamin C tablet, crushed is enough.
Unadulterated vitamin C hard to obtain
I find it harder to buy plain vitamin C tablets from supermarkets now. Everything seems to be flavoured or chewable, not ideal for breadmaking.
Amazon now sell ascorbic acid in powdered form: 500g for £4.30 [Amazon Prime]