Abstract: A device or sachet (3) for maintaining or modifying the atmosphere in a package suitable for meat, beef, lamb, pork, etc. the device including at least two containing layers (4, 5), a moisture activated chemical substance (6) contained by the containing layers, and at least one absorbent layer (7). Moisture within the package is soaked up by the absorbing layer. The moisture is then transferred from the absorbing layer to permeate through a micro-porous layer (5) as water vapor and activate the chemicals. The gas produced by the chemicals then passes through the sachet and into the package's atmosphere. This modifies the atomosphere to ensure that there is an adequate quantity of CO2 for achieving the desired shelf life of the packaged food.