As the name suggests, citric acid is a compound that occurs naturally in citrus fruits. It is used as a flavouring and an acidifier in a wide variety of foods and drinks including sweets, preserves and jellies as well as in other household products such as candles and bath bombs.
Citric acid is also known as ‘sour salt’ because it looks like coarse salt crystals but has a distinctive taste reminiscent of citrus fruit. Indeed, those following a low sodium diet sometimes substitute citric acid for salt in recipes to give a hit of flavour.
It has a variety of other uses: adjusting the pH when brewing beer and making wine; preventing the fats in home-made ice cream from separating from one another; and preventing fermentation in home-made cordials such as elderflower and lemon.
Citric acid in sweets
Citric acid is used for its flavour in a variety of sweets, especially those that have sour or fizzy flavours. Citric acid is one of a few types of food acids that are used to create the perfect balance between sweet and sour.
The acid mix is usually applied as a coating on the outside of sour sweets. The acids give off hydrogen ions that stimulate the sour taste receptors on the tongue. Compounds with low pHs, such as citric acid, also react with sugar to prevent it from crystallizing. This is useful when making sweets such as caramel where the melted sugar needs to be smooth with no crystals.
The citric acid prevents the sucrose in table sugar from forming crystals when it cools down. This makes it easier to work with as it allows additional time to combine ingredients without the mixture crystallising. This is particularly useful when making sweets such as pralines and brittles.
Citric acid in breadmaking
Some of the most common uses of citric acid rely on its chemical properties. Anyone who has made sourdough bread will know that a starter is used to impart the unique flavour. The starter is a fermented mixture of flour and water that turns into an active colony of yeast and bacteria that combine to become the leavening agent as the dough proves.
These microbes thrive in an environment rich in natural acids and starters can be enhanced with citric acid in order to improve the flavour. It also increases the speed at which the yeast ferments which can have an effect on the structure and consistency of the final loaf.
Citric acid in cheesemaking
One other use for citric acid is cheesemaking. In much the same way as it does in breadmaking, citric acid creates a favourable environment for the bacteria that ripen cheese. Citric acid is a key ingredient in mozzarella and ricotta cheeses in which it works as a chelating agent, collecting calcium atoms from the cheese mixture to create the desired texture.
Cheese is made by encouraging the casein proteins that are naturally present in milk to come together. The casein proteins are naturally negatively charged at the natural pH of milk and so repel one another. This can be overcome by adding citric acid as the change in pH effectively neutralises the negative charges of the casein proteins and allows them to come together to form curds. This process is aided by the addition of rennet, which makes it easier to separate the curds from the watery whey.
The chemistry of food production relies on a number of carefully managed reactions and relies on creating perfectly balanced environments. From promoting bacterial growth to preserving fresh fruit and veg and even making sherbet and popping candy, citric acid is an essential element in an experimental chef’s store-cupboard.