Sodium metabisulphite, the commercially produced salt of sulfurous acid, is a preservative used to extend the shelf life of meat products such as fresh sausages and burgers, even though it can have adverse effects on some people, especially asthmatics. Sodium metabisulfite is not permitted in several countries for use in meat products. Chemically, sodium metabisulfite contains 67% sulfur dioxide.
When sodium metabisulfite is applied to a meat product, it instantly reacts with water and, as a rule of thumb, around 50–55% added sodium metabisulfite can be found analytically in the meat product as SO2. Some SO2 is ‘lost’ as a result of countless reactions and cannot be detected any longer.
Therefore meat products are not analyzed with regard to their sodium metabisulfite content. The level of SO2 has to be measured instead and food standards refer to the SO2 level, rather than the sodium metabisulfite level, of a product. In many countries, 500 ppm of SO2 is the maximum per kilogram of fresh sausage.
In the UK, sodium metabisulfite is permitted in certain meat products only and it is not permitted in most other countries within the EU. One of the reasons that it is not permitted in some countries is that sodium metabisulfite causes a significant loss in vitamins such as thiamin in foods.