Most oxygen scavenging systems are based on the oxidation of iron and depend on the incorporation of an oxygen-scavenging component into the package, rather than an active packaging material. Ferrous iron powder is often used as the active agent. It is typically contained in a small high oxygen-permeable sachet to separate it from the food product (see Fig. 4.1). A disadvantage of systems of this type is that the water activity of the product must be high enough for the moisture to trigger the scavenging reaction.3 The sachet also poses a real risk to consumers as large amounts of iron could be accidentally ingested and there is the danger that it could leak, causing contamination or undesirable changes in the odour and flavour