Sodium metabisulfite is a chemical compound commonly used in the food industry for several purposes, so individuals might seek information about it. Sodium metabisulfite is a relatively common food additive, but many people are not familiar with what it is or how it is used. Searching online can be a good way to learn more about this additive and its potential effects on health. So if you are one of those who are curious about it, this blog post will guide you.

Let’s jump right in.

WHAT IS SODIUM METABISULFITE?

Sodium metabisulfite, a white or yellowish-white crystalline powder with a pungent sulfur odor. In Europe, it is denoted by the E number E 223, when used as a food additive. It is a chemical compound with the formula Na₂S₂O₅. Its molecular structure endows it with unique properties and reactivity.

One notable characteristic of sodium metabisulfite is its high solubility in water. When introduced to water, it readily dissolves, forming sodium bisulfite (NaHSO3) and releasing sulfur dioxide gas (SO2). The release of SO2 is responsible for the compound’s pungent sulfur odor, making it easily identifiable.

Chemically, sodium metabisulfite is classified as a reducing agent, meaning it can donate electrons to other substances. This property is central to its various applications.

In water treatment, it is utilized to reduce or eliminate chlorine and chloramine, thus making it valuable for dechlorination purposes. It is used in ore processing to reduce metals like gold and silver. In photographic development, it serves as a reducing agent to convert silver ions into metallic silver, aiding in image formation.

Within the food industry, sodium metabisulfite serves dual purposes as both a preservative and an antioxidant. Its pivotal function involves thwarting the browning of fruits and vegetables by impeding both enzymatic and non-enzymatic browning reactions. Additionally, it contributes to maintaining the color, flavor, and texture of diverse food items, all the while suppressing the proliferation of microorganisms that could cause spoilage.

FUNCTIONS IN FOOD

Sodium metabisulfite serves multiple functions in the food industry, including as a preservative to extend shelf life, an antioxidant to maintain color and flavor, and a bleaching agent to lighten the color of certain food products.

Let’s discuss in more detail.

Bacterial inhibitor in beer, ale, and wine

Sodium metabisulfite is a widely used chemical compound in the winemaking and brewing industries. Its role is particularly significant in the production of wine, ale, and beer. As a strong antimicrobial agent, sodium metabisulfite helps to control and prevent bacterial growth during the fermentation and aging processes. This ensures the quality and stability of these alcoholic beverages.

In winemaking, the control of bacteria is crucial for achieving the desired flavor and aroma profiles. Undesirable bacteria can lead to off-flavors and spoilage, which can ruin a batch of wine. When added to grapes, sodium metabisulfite inhibits vacterial growth by releasing sulfur dioxide (SO2) gas. This SO2 gas acts as a powerful antimicrobial agent, inhibiting the growth of unwanted bacteria, yeasts, and molds. This ensures that the wine fermentation proceeds with the selected yeast strains and prevents spoilage that could negatively impact the final product.

Similarly, in the brewing of ales and beers, the presence of bacteria can lead to the development of off-flavors and turbidity in the beer. By adding sodium metabisulfite, bacterial growth is inhibited. This ensures that the chosen yeast strains dominate the fermentation process and produce a consistent and desirable beer flavor.

Antifermentative agent in sugar and syrups

As a powerful inhibitor of fermentation, sodium metabisulfite helps prevent unwanted microbial growth and the conversion of sugars into alcohol or organic acids in sugar and syrup solutions.

In the sugar industry, the prevention of fermentation is essential to maintain product consistency. Microorganisms such as yeasts and bacteria can metabolize the sugars in syrups. This can lead to changes in flavor, texture, and the development of off-flavors. Sodium metabisulfite is added to sugar solutions to create an unfavorable environment for these microorganisms, inhibiting their growth and metabolic activity.

Syrup manufacturers also use sodium metabisulfite to extend the shelf life of various syrup-based products. Fruit syrups, corn syrup, and flavored syrups often contain sodium metabisulfite. By preventing fermentation, the antifermentative properties of sodium metabisulfite help maintain the sweetness, texture, and overall quality of the syrups over time, preventing them from becoming sour or alcoholic.

The usage of sodium metabisulfite as an antifermentative agent requires careful consideration of dosage and monitoring to ensure the desired effect is achieved without negatively impacting the taste or safety of the product. Excessive use of sodium metabisulfite can lead to an undesirable sulfur dioxide taste or create allergenic concerns, so precise control is essential.

Antibrowning additive in cut fruits, dried fruits, peeled potatoes, and maraschino cherries

Sodium metabisulfite is a widely used antibrowning additive in the food industry, particularly in products such as cut fruits, dried fruits, peeled potatoes, and maraschino cherries. Browning in these foods occurs due to enzymatic reactions when they are exposed to oxygen. The discoloration not only affects the visual appeal but can also alter the taste and overall quality of the food. Sodium metabisulfite serves as an effective solution to counteract these undesirable browning reactions.

Cut Fruits: When fruits are cut or sliced, they are particularly prone to browning due to the release of enzymes like polyphenol oxidase. By adding sodium metabisulfite to cut fruits, food processors can inhibit these enzymes and prevent the browning process. This is especially important for fruit platters, salads, and other dishes where the presentation is vital.

You might also like: Enzymatic And Non-enzymatic Browning

Dried Fruits: During the drying process, fruits can undergo browning reactions, which impact their appearance and flavor. Sodium metabisulfite is used either as a pre-treatment or as a preservative in dried fruits. It not only maintains the natural color but also extends the shelf life of products like apricots, apples, and raisins.

Peeled Potatoes: Peeled and sliced potatoes are staples in many dishes, but they are highly susceptible to browning, which can affect their visual appeal. Sodium metabisulfite is applied to these potato products to inhibit enzymatic browning, ensuring they remain appetizing in appearance.

Maraschino Cherries: Maraschino cherries are preserved in a syrup or brine solution. Sodium metabisulfite is introduced into the preserving liquid to prevent cherries from browning and to maintain their bright red color. This not only preserves their visual appeal but also their characteristic flavor.

SAFETY CONSIDERATIONS

To ensure the safe utilization of sodium metabisulfite, global regulatory authorities have instituted maximum permissible limits for its inclusion in food products. In the United States, the U.S. Food and Drug Administration (FDA) recognizes sodium metabisulfite as generally safe (GRAS) when employed in adherence to good manufacturing practices.

In the European Union, the European Food Safety Authority (EFSA) established a temporary group acceptable daily intake (ADI) of 0.7 milligrams per kilogram of body weight per day in 2016. However, in 2022, EFSA issued a subsequent evaluation regarding the safety of sulfur dioxide-sulfites. The conclusion indicated that the uncertainties identified in the 2016 reassessment had not significantly diminished. Consequently, EFSA withdrew the temporary group ADI, determining that the available toxicity database lacked adequacy to derive an ADI for sulfur dioxide-sulfites.

Allergies and Sensitivities

A key safety concern linked to sodium metabisulfite revolves around its capacity to induce allergic reactions in specific individuals. Sulfites, including sodium metabisulfite, have the potential to trigger sensitivity or allergies in some people. Allergic responses may manifest in mild symptoms like skin rashes, itching, and hives, while more severe reactions such as difficulty breathing and, in extreme cases, anaphylaxis can occur.

individuals with known sensitivities or allergies to sulfites should exercise caution and be aware of potential adverse reactions when exposed to products containing sodium metabisulfite.

Asthma and Respiratory Issues

Individuals with asthma or other respiratory conditions may be more susceptible to adverse effects from sodium metabisulfite. Sodium metabisulfite is toxic in inhalation. Inhalation of the compound’s fumes or dust particles could irritate the airways and trigger asthma attacks. Food processing facilities that handle sodium metabisulfite should have proper ventilation systems and take necessary precautions to minimize the release of sulfite fumes into the air.

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For the most of us, whenever we hear the words “bacteria”, “fungi” or “microorganisms”, the first things that come to mind are negative things such as diseases. Well, it is definitely true that there microorganisms that do us harm. But not all the time. Let’s talk about Escherichia coli (E. coli) for example. One particular strain of E. coli is O157:H7. Someone who ingested food that is contaminated with this strain of E. coli may experience food poisoning with severe symptoms. But for most of the time, E. coli does that cause harm or adverse health effects. In fact, this bacteria lives in our intestines and those of animals.

The negative connotations associated with microorganisms is undeserving. And on the contrary, many of them are beneficial in different fields or industries. In medicine, without microbes, we would be able to produce vaccines and antibiotic. Soil microbes help farmers recycle plant materials and decompose organic matter.

In the food industry, a lot of food products that we enjoy now would not have existed without them. One species of yeast that we have worked with for thousands of years is Saccharomyces cerevisiae. This fungus is one of the most important in the food industry. It has been used extensively in the manufacture of fermented beverages such as wine and beer, distilled beverages such as vodka and rum, and baked goods. But the strains of Saccharomyces cerevisiae involved in the manufacture of these products vary tremendously.

Let’s discuss further.

WHAT IS SACCHAROMYCES CEREVISIAE?

Like other species of yeasts, Saccharomyces cerevisiae is a eukaryotic, unicellular microorganism. The cells can exist in two forms: haploid or diploid. Most cells exist in diploid form, in which the cells are ellipsoid-shaped with a diameter of 5-6um, Cells in haploid form are spherical with a diameter of 4um.

Cells reproduce both sexually and asexually.

More often, S. cerevisiae reproduce asexually. In a process called budding, a haploid cell undergoes mitosis, forming new haploid cells or daughter cells that bud off the mother cell. The new cell grows bigger until it reaches the size of the mother cell and separates.

During sexual reproduction, two different haploid yeast cell mate, forming a diploid cell. This diploid cell then undergoes mitosis to form zygotes.

S. cerevisiae is a facultative anaerobe—it grows well aerobically and anaerobically. In nature, S. cerevisiae is commonly found in ripe fruits, particularly grapes. All strains can feed aerobically on sugars, including glucose, maltose, and trehalose, but not on disaccharide lactose and cellobiose. Anaerobically, some strains do not grow on trehalose and sucrose. Among these sugars, S. cerevisiae prefers glucose the most.

A 1977 study found out the optimum temperature for rapid growth of all strains of S. cerevisiae to be between 86 °F (30 °C) to 95 °F (35 °C).

Since it is easy to culture, S. cerevisiae is the most studied eukaryote. In fact, S. cerevisiae was the first ever eukaryote genome to be fully sequenced in 1996. The S. cerevisiae genome is made up of over 12 million base pairs and over 6000 genes, packaged in 16 chromosomes. Visit the Saccharomyces Genome Database for more on this.

Brewing

It is hard to pinpoint the exact origin of beer fermentation. But according to history, the oldest piece of evidence was a chemically confirmed barley beer found in modern day Iran.

Basically, beer is produced using germinated cereal grains (referred to as malt), flavoring like hops, water (which accounts for 93% of beer by weight), and yeasts. Yeasts are perhaps the most important ingredient in beer brewing. It is largely responsible for beer’s final characteristics—the alcohol content, appearance, aroma, and flavor—through a process called alcoholic fermentation.

When yeasts are added, they start feeding off the sugar available. The sugars in beers are mostly maltose, a dissacharide. The sugars consumed by yeasts are converted into alcohol and carbon dioxide. The final ethanol content by weight of beers vary from about 3% to 8%. Carbon dioxide is responsible for that fizz sound whenever we open a can of beer. However, CO2 produced during fermentation is allowed to escape. Oftentimes, brewers increase the carbonation by introducing pressurized CO2. Beer fermentation takes a week to several months to complete. This mainly depends on the type of beer (strength) and the yeast involved.

Once fermentation has finished, the beer is conditioned. This is where the yeast settles at the bottom of the fermentation tank, clarifying the beer. The yeast can be collected and reused for the next brewing process.

Around the world, there are over a hundred beer styles that exist. These include lagers, ales, and stouts. One main difference between these beers is how they are fermented. Ale beers are produced using S. cerevisiae yeast at temperatures of 53.6 °F to 64 °F. Whereas lagers are produced using Saccharomyces carlsbergensi yeast at a colder temperature of 46.4 °F to 53.6 °F. Both both ales and lager beers can be dark or light in appearance.

Baking

There are generally 3 main types of leavening agents in baked products. These include physical leaveners such as air or steam, chemical agents such as baking soda and baking powder, and biological agents such as yeast. Unsurprisingly, the species of yeasts more synonymous with baking is S. cerevisiae. This is why S. cerevisiae is also called baker’s yeast.

Occasionally, bakers use other species of yeast in baking. Saccharomyces exiguus is typically used as sourdough yeast.

Baker’s yeast come in several forms. In commercial baking, where the daily production volume is immense, cream yeast is used. Cream yeast looks similar to a yeast slurry. It is about 85% water and 15% S. cerevisiae yeast. Cream yeast only lasts for up to 10 days, so refrigeration and additional equipment during storage is necessary.

Another form of yeast widely used in commercial baking is compressed yeast. Compressed yeast is similar to cream yeast, but contains less liquid. It is generally 70% water and 30% yeast. Like cream yeast, compressed yeast has a very short life span. For this reason, compressed yeast is now less common, especially in developing countries.

Active dry yeast and instant yeast are common forms of yeast for baking at home. In many home recipes, both forms can be used interchangeably. The main difference between the two is that active dry yeast requires dehydration before use. Whereas instant yeast can be added and mixed directly with other ingredients. Instant yeasts also requires less time to rise.

One advantage of active dry yeast has a longer shelf life than other forms of yeast. It can last for a year at room temperature.

Winemaking

Wine is an alcoholic drink generally made from fermented grape juice. Like in brewing beer, the addition of S. cerevisiae yeast converts the sugar in the fruit into ethanol and carbon dioxide.

Some winemakers use wild yeast to ferment wine for more interesting complex flavors. Thousands of years ago, wines were fermented using wild or “natural” yeasts. They tend to be more active once the grapes have matured enough. However, one major flaw of using wild yeast is its unpredictable nature. And a lot of wild yeasts do not produce quality wine. Most of these yeasts belong in the Kloeckera and Candida genera.

In order to produce quality wines consistently, commercial wineries inoculate strains of S. cerevisiae yeast.

Throughout history, vintners or winemakers have used fruits (apple wine) other than grapes, vegetables, and grains (rice wine such as sake). But wine varieties made from these do not usually produce wine with qualities similar to those made from grapes. The main reason for this is that they contain less fermentable sugars and water to maintain proper fermentation.

Grapes are high in sugars. The initial sugar content of the grape juice dictates the alcohol level of the resulting wine. Unripe grapes contain predominantly glucose. Ripe grapes contain equal amount of glucose and fructose, both of which are fermentable sugars. Other sugars in the grapes in smaller amounts include pentoses, cellobiose, and galactose, all of which are unfermentable sugars.

After fermentation, the wine can have an alcohol or ethanol content between 11-13% on average. This depends on several factors such as the wine variety and the winemaker. For example, some winemakers intentionally stop the fermentation process before the yeast converts of all the sugars into alcohol. This results in a sweeter wine.

Other references

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

M. Wallert, K. Colabroy, B. Kelly, J. Provost (2016). The Science of Cooking: Understanding the Biology and Chemistry Behind Food and Cooking. John Wiley & Sons, Inc.

J. Jay, M. Loessner, and D. Golden (2005). Modern Food Microbiology (7th Edition). Springer

O. Zaragoza, A. Casadevall (2021), Encyclopedia of Mycology, Elsevier.

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