POTASSIUM METABISULFITE

CAS: 16731-55-8 ANTIMICROBIAL AGENT, ANTIOXIDANT, COLOR OR COLORING ADJUNCT, DOUGH STRENGTHENER, FLOUR TREATING AGENT, OXIDIZING OR REDUCING AGENT

Potassium metabisulfite is a sulfite-based food additive used primarily as an antimicrobial and antioxidant agent in food and beverage processing, with a Codex INS number of 224 and recognized in JECFA specifications.

What It Is

Potassium metabisulfite is a chemical additive classified in food systems as a sulfite compound with multiple technical functions including antimicrobial, antioxidant, color or coloring adjunct, dough strengthener, flour treating agent, and oxidizing or reducing activities. It is identified by the CAS number 16731-55-8 and is recognized by the Codex Alimentarius with an International Numbering System (INS) identifier of 224, indicating its inclusion in the global food additive nomenclature. Other names used for this compound reflect its chemical nature and salt forms, including dipotassium disulfite, dipotassium pyrosulfite, disulfurous acid dipotassium salt, potassium pyrosulfite, and pyrosulfurous acid dipotassium salt. In physical form, potassium metabisulfite typically appears as a white to pale yellow crystalline powder or granules that release sulfur dioxide when dissolved in water, which underlies much of its functional behavior in food matrices. In food science and regulatory contexts, potassium metabisulfite belongs to the class of sulfite additives, representing salts of sulfurous acid. These salts, including sodium metabisulfite and potassium metabisulfite, are known to interconvert and release sulfur dioxide under certain conditions such as dissolution or acidic environments. The release of sulfur dioxide is a key aspect of how this additive exerts antimicrobial and antioxidant effects in food and beverage applications. As an ingredient, it is used with good manufacturing practice and within regulatory limits set by authorities such as the U.S. Food and Drug Administration (FDA) and the Joint FAO/WHO Expert Committee on Food Additives (JECFA). The inclusion of this compound in regulatory inventories reflects both its utility in preservation and the need for controlled use in specific food categories.

How It Is Made

Potassium metabisulfite is produced through controlled chemical reactions involving sulfur dioxide and potassium-containing bases. At an industrial level, a typical manufacturing route begins with the reaction of sulfur dioxide gas with potassium hydroxide or potassium carbonate in aqueous solution to form intermediate potassium sulfite species. Continued introduction of sulfur dioxide to the system under controlled temperature and pH conditions leads to the formation of bisulfite species. Upon removal of water and through crystallization processes, the bisulfite species dehydrate to form potassium metabisulfite (K2S2O5) as a solid crystalline product. These steps are conducted within chemical manufacturing facilities that implement quality control measures to ensure that the food-grade product meets defined purity and contaminant limits. Food-grade potassium metabisulfite is subject to specifications established by regulatory bodies and international compendia, such as the JECFA monographs, which detail acceptable limits for impurities, heavy metals, water insolubles, and other quality parameters. The manufacturing process is designed to produce a compound with consistent functional performance in food systems while minimizing unwanted byproducts. The solid form is typically white to pale yellow crystals or powder, indicating its composition and physical state suitable for incorporation into various food and beverage formulations. In packaging and storage, attention is paid to minimizing exposure to moisture and air, as these conditions can accelerate the release of sulfur dioxide and reduce product stability. During production and handling, safety protocols address the potential for sulfur dioxide release, which can be irritating to mucous membranes. Facilities producing potassium metabisulfite implement appropriate ventilation and worker protection measures, and the product is supplied with certificates of analysis that document compliance with food-grade specifications. For food applications, manufacturers follow guidelines on permissible levels and use conditions to ensure that the additive functions effectively without exceeding regulatory limits for total sulfite content or residual sulfur dioxide in finished products.

Why It Is Used In Food

Potassium metabisulfite serves several technological roles in food and beverage production. Its principal utility stems from its ability to release sulfur dioxide under processing conditions, which acts as both an antimicrobial and antioxidant agent. As an antimicrobial, the released sulfur dioxide and its associated sulfite species exert inhibitory effects on a range of spoilage microorganisms, including certain yeasts, molds, and bacteria. This antimicrobial action is particularly valuable in products where microbial stability influences shelf life, quality, and safety outcomes. For example, in winemaking, sulfite-based additives help control wild yeast and lactic acid bacteria during fermentation and subsequent storage, contributing to consistent product quality. In addition to microbial control, potassium metabisulfite functions as an antioxidant by scavenging oxygen and reactive oxidative species that can cause undesirable changes in color, flavor, and nutritional components. Oxidative browning in fruit juices and other plant-based products can lead to consumer rejection; the antioxidant properties of sulfite additives help mitigate these changes and preserve desired sensory attributes. For this reason, potassium metabisulfite is used in dried fruit processing, certain juice preparations, and other food systems where color preservation and oxidative stability are priorities. Other functional contributions include its use as a dough strengthener and flour treating agent, where oxidizing or reducing properties improve dough handling and baking performance. In these contexts, the additive interacts with gluten proteins and influences the network formation that underpins dough elasticity and gas retention. The oxidizing or reducing actions contribute to improved dough structure and baked product quality, especially in formulations with specific performance requirements. Overall, the incorporation of potassium metabisulfite is motivated by its multifaceted functionalities that support microbial stability, oxidative protection, and processing performance across diverse food and beverage applications.

Adi Example Calculation

To illustrate how a group acceptable daily intake (ADI) expressed as sulfur dioxide functions, consider a hypothetical adult with a body weight of 70 kilograms. If the group ADI is framed in terms of sulfur dioxide, regulatory assessments consider total sulfite exposure from all dietary sources relative to this body weight. If a food product contains sulfite-derived sulfur dioxide at levels within regulatory limits, the contribution of that product to total daily sulfite exposure would be calculated as milligrams of sulfur dioxide per kilogram of body weight. By summing exposures from multiple foods that contain sulfite additives, a total daily intake can be estimated and compared to the ADI threshold. In this illustrative example, a 70-kilogram adult consuming several foods with sulfite additives might achieve a total sulfur dioxide equivalent exposure that remains below the ADI when use levels and consumption patterns align with regulatory good manufacturing practice. This type of calculation helps regulators and food producers assess whether typical consumption scenarios are consistent with safety benchmarks, reinforcing the importance of adhering to permissible use levels and labeling provisions for sulfite-containing products.

Safety And Health Research

Potassium metabisulfite and other sulfite additives have been the subject of regulatory evaluations focusing on their safety profile when used within defined food applications. The primary aspects of safety assessment for sulfite compounds include evaluating potential allergenicity, respiratory effects in sensitive populations, and the metabolic handling of sulfur dioxide and related species released during use. Regulatory bodies such as JECFA have grouped sulfite compounds for safety evaluation, recognizing commonalities in their behavior and setting intake guidance expressed as sulfur dioxide to account for shared metabolic pathways. Research on sulfite additives often addresses the potential for hypersensitivity reactions in susceptible individuals. Some people exhibit sensitivity to sulfites, which can manifest as respiratory discomfort or other responses; this consideration has informed labeling requirements in various jurisdictions. Regulatory systems may mandate that products containing sulfites above defined thresholds disclose this information to assist consumers in identifying foods that contain these additives. Such labeling provisions aim to protect populations who experience sensitivity without implying broad adverse effects for the general population. Toxicological evaluations consider endpoints such as acute toxicity, genotoxicity, and chronic exposure outcomes. The grouping of sulfite compounds by JECFA and other authorities reflects an understanding of their shared behavior as sulfur dioxide-releasing agents and the need to evaluate total exposure to sulfite-derived sulfur dioxide rather than individual salts in isolation. These evaluations inform acceptable daily intake guidance and support international harmonization of safety criteria. The absence of definitive associations between regulated use levels of potassium metabisulfite and adverse outcomes in the general population underpins continued regulatory acceptance within defined use conditions. Safety research also examines context-specific factors such as the impact of exposure route, the chemical environment in food matrices, and the influence of coexisting food components. By focusing on functional performance in food systems and human exposure potential, regulatory risk assessments integrate multiple lines of evidence to inform allowable use levels and labeling conditions. While research continues to refine understanding of sulfite behavior and potential sensitivity responses, existing evaluations provide a foundation for safe and informed use of potassium metabisulfite in food and beverage applications when appropriate conditions are followed.

Regulatory Status Worldwide

In the United States, potassium metabisulfite is recognized in the U.S. Code of Federal Regulations at 21 CFR 182.3637, where it is listed as generally recognized as safe (GRAS) when used in accordance with good manufacturing practice. The regulation specifies that it should not be used in meats, foods recognized as a source of vitamin B1, or on fresh fruits and vegetables intended to be served raw or presented to consumers as fresh. This position reflects historical regulatory assessments and the broader classification of sulfite additives in food processing contexts, including labeling and use restrictions. The conditions of use and limitations are codified in the eCFR entry for section 182.3637, which outlines permissible applications and restrictions on use in certain food categories. Internationally, potassium metabisulfite is identified with the Codex Alimentarius International Numbering System (INS) number 224, indicating its inclusion in the global enumeration of food additives. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has evaluated potassium metabisulfite and related sulfite compounds, establishing a group acceptable daily intake (ADI) expressed as sulfur dioxide to reflect the shared metabolic and functional characteristics of sulfite species. JECFA’s specifications and safety evaluations are published in monographs and compendia that define quality and purity criteria for food-grade products and support international regulatory harmonization. In the European Union and other regions that adopt E numbers for food additives, potassium metabisulfite is commonly referred to as E224, reflecting its assignment under the INS. Regulatory frameworks in the EU require food labels to indicate the presence of sulfites when concentrations exceed defined thresholds, and specific maximum levels may apply to particular food categories. Labeling rules ensure that consumers are informed about the presence of sulfites, which can be relevant for individuals with sensitivity. Overall, the regulatory status of potassium metabisulfite involves both allowances for use within defined technical functions and labeling or limitation conditions to ensure consumer information and safety.

Taste And Functional Properties

Potassium metabisulfite itself does not contribute a pronounced flavor at the low levels typically used in food and beverage applications. When dissolved, it releases sulfur dioxide, which at higher concentrations can impart a characteristic sharp, pungent note reminiscent of sulfurous or atmospheric undertones. In properly formulated products, the concentrations are managed to achieve functional benefits without imparting detectable off flavors. In beverages such as wine and cider, the perceptible influence of sulfite-derived sulfur dioxide is often masked by the inherent sensory complexity of the product, and regulatory limits on total sulfite content guide formulation to balance stability with sensory acceptability. Functionally, potassium metabisulfite is highly soluble in water, which allows it to disperse rapidly in aqueous food matrices. The efficacy of its antimicrobial and antioxidant actions depends on factors such as pH, temperature, and product composition. Lower pH environments favor the presence of molecular sulfur dioxide, which is more effective as an antimicrobial agent. As a result, acidic products like wine and fruit juices benefit from enhanced activity at lower pH levels. In dough systems, the additive’s reducing or oxidizing behavior is influenced by interactions with proteins and other components, and processing conditions such as mixing and fermentation can modulate its functional impact. The stability of potassium metabisulfite is another important attribute; while it is stable in dry form, exposure to moisture and air gradually leads to the release of sulfur dioxide. As such, storage in sealed, moisture-resistant containers helps maintain product integrity until use. In functional performance, its ability to contribute to microbial and oxidative control without altering the core sensory attributes of many food products makes it a versatile additive in food processing.

Acceptable Daily Intake Explained

An acceptable daily intake (ADI) is a regulatory concept used to express the amount of a substance that can be consumed daily over a lifetime without appreciable health risk. For sulfite compounds, including potassium metabisulfite, regulatory evaluations have established a group ADI expressed as sulfur dioxide, which reflects the shared metabolic and functional characteristics of these chemically related compounds. This grouping recognizes that multiple sulfite salts release sulfur dioxide under physiological conditions, and the ADI is therefore framed in terms of the common moiety rather than the parent salt alone. The ADI provides a reference point for regulatory authorities and food producers to consider total exposure from all sources of sulfite additives. By defining an ADI expressed as sulfur dioxide, regulatory frameworks aim to ensure that the cumulative intake of sulfite species from various foods and beverages remains within a range considered safe for most individuals. The concept of good manufacturing practice plays a role in ensuring that use levels of additives like potassium metabisulfite are limited to what is technologically necessary for their intended functions. The ADI does not represent a target level to be achieved or recommended as a daily consumption amount; rather, it provides a boundary for regulatory assessment and risk management. For individuals with specific sensitivities or conditions related to sulfite exposure, labeling requirements and consumer information provisions help identify products that contain sulfite additives, enabling informed choices. In this way, the ADI functions as part of a broader regulatory system that balances technological benefits with safety considerations in food and beverage production.

Comparison With Similar Additives

Potassium metabisulfite shares functional characteristics with other sulfite-based food additives, including sodium metabisulfite (INS 223) and sulfur dioxide (INS 220). All of these compounds serve as antimicrobial and antioxidant agents in food and beverage applications, with their efficacy linked to the release of sulfur dioxide under processing conditions. Comparatively, potassium metabisulfite may be selected in formulations where the presence of potassium ions is preferred or where specific solubility or handling characteristics align with processing needs. Sodium metabisulfite performs similar roles but introduces sodium ions, which may influence formulation decisions based on nutritional or flavor considerations. Sulfur dioxide itself, designated as INS 220, represents the simplest form of sulfite additive and delivers antimicrobial and antioxidant benefits directly as the gas. However, handling and dosing sulfur dioxide gas pose practical challenges in many food processing settings, making solid salts like potassium metabisulfite and sodium metabisulfite more convenient and controllable sources of sulfite functionality. Differences among these additives also extend to labeling requirements and consumer perception, as products containing sulfite salts may require declaration of sulfite content when thresholds are exceeded. By comparing these related additives, food scientists weigh factors such as solubility, ionic composition, ease of handling, and regulatory conditions to select the appropriate sulfite source for a given application. Each additive contributes to achieving similar preservation and oxidative control objectives while offering distinct practical considerations in formulation and processing.

Common Food Applications Narrative

Potassium metabisulfite finds broad application across food and beverage categories where microbial stability, oxidative control, and processing performance are essential. In winemaking and cider production, it is often used during crushing, fermentation, and aging stages to help control wild yeasts and spoilage microbes and to protect color and flavor during storage. Winemakers may introduce the compound in measured amounts that release sulfur dioxide, thereby contributing to both preservation and antioxidant protection in products that are sensitive to oxygen exposure. In the production of fruit juices and concentrates, potassium metabisulfite can be used to curb oxidative browning and maintain visual appeal. Fruit-based products such as lemon juice, apple juice, and other citrus preparations are prone to enzymatic and nonenzymatic browning reactions, and the inclusion of sulfite additives supports color retention and shelf life. Similar logic extends to dried fruit processing, where the treatment of products such as apricots and raisins helps preserve vibrant color and reduces microbial spoilage risk during extended storage periods. Other applications include its use in beer brewing, although it is less common in this category compared with wine, as wort boiling provides significant microbial control. Nevertheless, in specific craft or specialty brewing contexts, potassium metabisulfite may be selected to manage microbial quality when desired. In bakery applications, its functional properties as a dough strengthener and flour treating agent contribute to improved dough handling and finished product texture. The additive may be used in select baking formulations where consistent performance is a priority. Across these applications, potassium metabisulfite’s role is to support quality and stability without dominating the sensory profile of the final product. Its inclusion is guided by regulatory conditions that define permissible use levels and labeling expectations, ensuring that consumer information on sulfite presence is transparent when required. By fulfilling multiple roles in diverse food systems, potassium metabisulfite remains a valuable tool for food scientists and processors seeking to balance safety, stability, and product quality.

Safety & Regulations

FDA

  • Approved: True
  • Regulation: 21 CFR 182.3637

EFSA

  • Notes: Specific EFSA numeric ADI not confirmed from authoritative source
  • E Number: E224

JECFA

  • Year: 1998
  • Ins Number: 224
  • Adi Display: 0-0.7 mg per kg body weight expressed as sulfur dioxide

Sources

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