Sulphites

Sulfites are salts and esters of sulfurous acid (H2SO3). The term commonly refers to the sulfite ion (SO3^2−) and the bisulfite ion (HSO3−), as well as their salts, such as sodium sulfite (Na2SO3) and potassium sulfite (K2SO3). In food and beverage contexts, sulfites and sulfur dioxide (SO2) are used as preservatives and antioxidants to prevent browning, inhibit spoilage, and protect against certain microbes.

In aqueous solutions, sulfite and bisulfite species exist in equilibrium with sulfurous acid. Under acidic conditions, sulfur dioxide is released from these species, which explains why monitoring pH and oxygen exposure is important in systems that contain sulfites.

Common applications include food and drink processing, where sulfites help preserve wines, dried fruits, fruit juices, and some processed vegetables. They are also used as dough conditioners and anti-microbial agents in certain products. Beyond food, sulfites are employed in the pulp and paper industry for bleaching, in textile processing, in photography, and in water treatment systems.

Health and regulation considerations focus on sulfite sensitivity. A small portion of the population experiences hypersensitivity or asthmatic reactions to sulfites, particularly in the context of inhalation or ingestion of sulfited foods and drinks. Because of these risks, many jurisdictions require labeling of foods and beverages that contain added sulfites above specified thresholds. Safety guidance emphasizes proper storage and handling to minimize oxidation and unintended release of sulfur dioxide gas.

Environmental and industrial aspects include the potential release of sulfites during combustion of sulfur-containing fuels and their management in processes designed to minimize emissions and effluent impact.