Sodium Metabisulfite

(or Sodium Pyrosulphite or E332)Created by: Bernadette Piffard

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What is Sodium Metabisulfite?
Sodium Metabisulfite is a compund that typically stays in a whitish yellow crystalline powder. In food it is an anti-oxidant preservative. It is used to eliminate oxygen in waste water and pipes, and removes chlorine. It bleaches, through oxidization, mechanical paper pulp, kaolin clay, wool, and cotton. It is used in processing many materials such as leather and textiles. (1) It is replaceable with Potassium Metabisulfite.

Why is it in our food and what is its purpose?
It is in our foods mainly as a preservative, specifically an antimicrobial preservative. That means it is very useful in keeping bacteria and other single-celled organisms out of your food. These organisms are what causes rotting. It is also very important in stopping bacterial growth in wine. It is good to note, however, any effects Sodium Metabisulfite has on you is less effective when ingested through water or wine.(2) It is mainly in dried foods such as potato chips, raisins, and dehydrated potatoes. It is in a lot of frozen foods such as frozen vegetables, and frozen shellfish. It is also in pickles and fruit juice. (3) So basically, it is found in most things intended to be preserved. It can be found in other things, however, due to its effectiveness. For example, it is part of the joy of an Almond Joy. Oh, joy!

Sodium Metabisulfite is in dried fruits
Sodium Metabisulfite is in dried fruits

What are its properties?
Sodium Metabisulfite loves water. It is hygroscopic and absorbs water from anywhere it can get it, including the air. From absorbing moisture it can become heavier then it actually is itself. This trait also makes it very soluble in water. Sodium metabisulfite with more than 65.0% concentration of Sulfite (SO2) releases sulfur dioxide when in water. (1) When with adlehyde and ketones it forms bisulfite adducts (a compund with all of the atoms of its original components). Basically, it creates bisulfite. In sulfonic acid it isolates adlehyde and ketones. It is stable in ordinary conditions.

What are the pros and cons to adding this to our food? Side effects?

  • No mold
  • No bacteria
  • No microbes or germs in your food
  • Hinders absorption of Thiamine (Vitamin B)
  • Increases excretion of calcium
  • Impairs growth in organic cultures (after all,
as a microbial preservative, it is what it is made

Sodium Metabisulfite, being a microbial preservative, is a negative factor in organic growth. In your food, this means a very limited amount of mold and bacteria. This is a very good thing, right? After all, who wants to bite into a moldy pickle? Wine would be impossible without bisulfites because they are a good source of sulfur dioxide. Without sulfur dioxide, wine would simply become vinegar, or rotten grape juice. I digress, let's look at the effect of sodium metabisulfite on organic cultures:

The addition of salts of SO2 caused stimulation of growth at lower levels and complete inhibition at 2000 ppm NaHSO3.” (2)

Sodium Metabisulfite stops growth of single celled-organisims and thus there would be no mold. Then, what is to stop it from stopping multi-celled organisms? They are both organic after all. Well, the average adult would have to eat 10 grams of sodium or potassium metabisulfite to die. It would take 30 to 100 mg for every kg of body weight to cause any adverse effects. (5) However, let's take a look at what these effects would be.

Sodium metabisulfite may hinder the body's digestion of thiamine, or vitamin b. In an experiment done by Causeret in 1965 that gave rats 160 g of thiamine with 120 g of potassium metabisulfite and compared it the urinary output to the urinary output of giving the rats just thiamine.(2) Here is what the experiment found:

It was found that the addition of SO2 greatly reduced the urinary output of thiamine, especially on the day when both were given together.” (2)

Too much sodium and potassium metabisulfite will prevent some of the vitamin b you eat from being processed; and note that this is all sodium sulfites, or anything containing sulfur dioxide or SO2. (2) Lack of vitamin b causes many ill-effects (see Thiamine Mononitrate). This is obviously not what one wants to see, but as a contrary point let’s look at an experiment done by Jaulmes in 1965:

In wine containing 400 ppm SO2, 50 per cent. of the thiamine was destroyed in one week. However, no loss of thiamine was observed in 48 hours. The small amounts of SO2, resulting from the recommended levels of usage in wine are therefore not likely to inactivate the thiamine in the diet during the relatively short period of digestion.” (2)

From this we can conclude, the small amounts you ingest is doubtful to do you harm. Besides, the effects of Sodium Metabisulfite is lessened when ingested through wine and water.(2) The amount you consume daily anyway is definitely something to sneeze at. The FDA estimates the average American consumes for each of their own kg of body weight, about 0.2 mg (5). Remember, 30 mg to 100 mg per kg of body weight is the magic number.(5)

Another experiment showed it would increase the amount of calcium excreted through feces and urine. One group of rats got 0.5 % of Calcium in their water, and another got 1%., while both groups got the corresponding amount of potassium metabisulfite (just like sodium metabisulfite). One last group only got calcium. This experiment was done by Causeret and Hugot.(2) Here are the results:

"At the lower level of dietary CA (0.5 per cent.) both levels of the metabisulfite caused a significant increase in the urinary excretion of Ca but had no effect on the faecal [feces or poop] excretion. At the higher dietary Ca lever (1 per cent.) the reverse was found." (2)

If too much Sodium Metabisulfite (or other Metabisulfites) are consumed, it would cause calcium deficiency. You would, however, have to consume much more than what the FDA allows.
One last note is that in the NFPA rating, it has recieved a 1 in health. (1) That means it is slightly hazardous and requires gloves and safety goggles to handle. (4) So, Sodium Metabisulfite isn’t really something you want to eat but then again, you don’t want to eat mold either. Tiny amounts are fine, but you should never, ever, ever, ever, ever, ever, ever, ever, ever, ever, start eating it for fun. We eat so little of sulfites in general, though, that you shouldn't really worry about it too much.

Conclusion: We eat such a small amount, you shouldn't worry too much, yet it is still nice to know that over-all, if too much is ingested, ill-effects happen, and to be on the look-out if you are allergic to sulfites.
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What does name tell us?
Sodium comes from the sodium cations (positively charged ions). Bisulfite is from the fact is is a sulfite created by replacing one or both of the hydrogen atoms of Sulfuric acid creates salts or esters (the sulfites). As for ‘meta’, also ‘pyro’, it tell us that it is an oxo acid created by an ortho acid being heated and losing water molecules. (1) That process is called dehydration, and is why Sodium Metabisulfite is hygroscopic.

Sulfur: 2
Oxygen: 5
Sodium ions: 2

Other names for it: “Dinatriumdisulfit; Disulfito de disodio; Disulfite de disodium; Disodium disulfite; Disodium Salt Pyrosulfurous Acid; Disulfurous acid, disodium salt; Pyrosulfurous acid, disodium salt; Sodium Metabisulfite; Sodium disulfite; Sodium Pyrosulfite,” (1)

Works Cited
(1) “Sodium Metbisulfite.” Chemicallland21. 2000-2008. Chemicalland21. November 2010 <>
(2) “041. Sodium Sulfite.” InChem Report Series No. 40A, B, C. International Programme on Chemical Safety in partnership with Canadian Centere for Occupational Health and Safety. November 2010 <>
(3) “E223 Sodium Metabisulfite.” University of Bristol: School of Chemistry. 2002-2010. University of Bristol. November 2010 <>
(4)”NFPA 704 Hazard Rating System” New Mexico State University. 2005. NMSU Board of Regents. November 2010 <>
(5)"Sodium Metabisulfite." FDA U.S. Food and Drug Administration. 31 November 2006. U.S. Department of Health and Human Services. 9 November 2010 <>