Although the process of extracting it is rather scientific, the acid itself is a natural, organic, non-test-tube product. The same citric acid listed in the ingredients for tomato sauce is what makes fruits like lemons and limes taste sour! It was originally produced by dehydrating and crystallizing lemons, though it was later discovered that certain strains of mold (like Penicillium) produced it much more efficiently.
As you might expect, one of the biggest uses of citric acid is to make things taste sour. It's found in sour candies, sodas, juices, and many pre-made foods. It's also a fairly efficient natural preservative and color-enhancer, which is why it's listed as an ingredient in many canned and preserved goods.
As for the citric acid in our cupboard? We keep it around for making cheese! Since it's so concentrated, citric acid is much better at getting milk to separate than straight lemon juice. In our research for this post, we also discovered that citric acid can be diluted in water and used as a household cleaner - maybe we'll try that next!
(Image: Emma Christensen)