What does bisulfite mean?
A bisulfite is a chemical compound containing the hydrogen sulfite anion, HSO₃⁻, which arises when sulfurous acid loses only one of its two acidic protons. Bisulfites most often take the form of salts — sodium bisulfite, potassium bisulfite, and ammonium bisulfite are the best known — though esters of the anion also exist. These compounds serve as versatile reducing agents and preservatives: they prevent discoloration in dried fruit, inhibit bacterial growth in wine and beer, dechlorinate water, and act as intermediates in industrial chemistry. In molecular biology, bisulfite treatment has become foundational to epigenetics, because it selectively converts unmethylated cytosines into uracils while leaving methylated cytosines intact, enabling researchers to map DNA methylation patterns through bisulfite sequencing. The term belongs chiefly to technical registers — chemistry texts, food-labeling regulations, and laboratory protocols — but the compounds themselves are quietly ubiquitous in everyday products. Understanding 'bisulfite' means grasping both a simple acid–base concept and a word with outsized practical importance across food preservation and modern genomic science.
nounA chemical compound containing the bisulfite anion (HSO₃⁻), formed by partial neutralization of sulfurous acid; bisulfites exist as salts, such as sodium bisulfite, or as esters.
- A salt or ester containing the hydrogen sulfite anion (HSO₃⁻), used as a reducing agent, preservative, and in DNA methylation analysis.
"The winemaker added a dash of sodium bisulfite to sterilize the barrels and prevent oxidation."
"Sodium bisulfite is widely used in the food and beverage industry to inhibit browning and microbial growth."
"In the laboratory, bisulfite treatment converts unmethylated cytosine residues to uracil, allowing methylated sites to be identified."
The plural is regular and appears mainly in technical writing when comparing different bisulfite salts or referring to multiple samples.
"Both potassium and sodium bisulfites are approved preservatives in many countries."
The same humble salt that keeps wine from spoiling also lets scientists read the epigenetic marks on your DNA — bisulfite sequencing is how researchers map methylation across the genome.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bisulfite
The word bisulfite combines the prefix 'bi-', indicating a hydrogen retained from partial neutralization of a dibasic acid, with 'sulfite', itself derived from 'sulfur' via the New Latin 'sulfur' and French 'sulfite'. It emerged in nineteenth-century chemistry alongside related terms such as 'bisulfate', as chemists systematized the naming of acid salts. Its cognates include the parallel formations 'bisulfate', 'bicarbonate', and 'biphosphate', all built on the same pattern of naming partially neutralized salts of dibasic acids.
How bisulfite is actually used
Bisulfite is primarily a technical term encountered in chemistry, food science, oenology, and molecular biology; it is rarely used outside scientific contexts. In older literature, 'acid sulfite' and 'hydrogen sulfite' appear as alternative names for the same anion or its salts.
Easily confused with bisulfite
Bisulfate contains the hydrogen sulfate anion (HSO₄⁻) derived from sulfuric acid, whereas bisulfite contains the hydrogen sulfite anion (HSO₃⁻) derived from sulfurous acid.
A disulfite (metabisulfite) contains the S₂O₅²⁻ anion linking two sulfite units, while a bisulfite contains a single HSO₃⁻ ion.