Citric Acid

How it's made

Made by fermenting sugars with Aspergillus mould.

Citric acid is the most widely used food acid in the world. It gives citrus fruits their sourness and is added to countless drinks, sweets and preserves to provide tartness, adjust acidity and act as an antioxidant helper by binding trace metals. Despite the citrus association, virtually none of the citric acid in food today is squeezed from fruit.

It is made by fermentation using the mould Aspergillus niger. The mould is fed a sugar source — typically glucose syrup from corn, or molasses — in large fermenters, and as it grows it secretes large quantities of citric acid into the liquid. This microbial process, developed in the early twentieth century, replaced extraction from lemons and made citric acid cheap and abundant.

Once fermentation is complete, the mould is filtered off and the citric acid is recovered from the broth, purified — classically by precipitating it with lime and then releasing it again with acid — and crystallised into the familiar white powder. The food-grade product is highly pure, and although the fermentation may use corn-derived sugar, the finished acid contains no protein from the starting material.