Citric acid is an organic acid, and is often used in a natural way as a preservative. A weak organic acid, citric acid is commonly used to give an acidic taste to soft drinks and some types of foods. Lemon and limes have a very high concentration of citric acid compared to grapefruits and oranges, and this can be up to 8% for the dry weight of each fruit.
The alchemist Jabir ibn Hayyan was believed to have discovered citric acid in the 8th Century. In the Middle Ages, certain fruits, such as lemon and lime, were known to contain acidic elements, but it wasn’t until 1784 that citric acid itself was first isolated. Swedish Pomeranian pharmaceutical chemist Carl Wilhelm Scheele made the discovery via crystallizing citric acid from lemon juice.
In the last decade of the 19th Century the production of citric acid increased markedly, and experiments by C. Wehmer established that citric acid from sugar could be produced from penicillium mould. James Currie, an American food chemist, was responsible, in 1917, for discovering the effectiveness of particular strains of the Aspergillus niger mould as being good sources for citric acid. The Pfizer pharmaceutical company capitalised on this technique on an industrial scale, and Currie’s technique has been widely used in industry right up to the present day. Citric acid is used today in the cosmetics and pharmaceutical industry, in cleaning solutions, food dyeing, and in photographic film developing. As a cleaning agent it can be used to remove limescale and hard water stains, and, when in a shampoo, can aid the removal of wax in the hair. The acid can also be produced in a dry and powdered form. This is commonly called sour salt, and will typically be used for culinary purposes.
Other Types of Organic Acids and Compounds
Benzoic acid is a type of organic acid that has a larger molecular1 mass compared to other organic acids, while salicylic acid is an organic acid that is colourless. This can be found naturally in a variety of unripe fruit and vegetables, including blackberries, blueberries, kiwi fruits, raisins, apricots, tomatoes, olives, green peppers, and radishes, as well as mushrooms and types of herbs and spices. Urea is an organic compound and can be used, together with ammonium phosphate, as a type of yeast nutrient. The subsequent fermentation process then results in sugars being turned into ethanol. Urea has many commercial uses, from skin cream and hair removers to a browning agent in pretzels.
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