## Shelf Life Oxygen

### Quick Start

This is a specialist app about how the oxygen content in food changes with time. It does some great industry-standard calculations if you need them. Otherwise it's an interesting lesson in how these sorts of things are done.

The shelf life of a food can depend on how long it takes to react with a specific amount of oxygen, q, expressed as %wt/vol. The analysis here follows the methodolgy and terminology of Prof Cooksey.

The question to be answered here is what thickness, L, of a given type of packaging material will be required to achieve a specific shelf life, t measured in months. For the problem we have the volume of the food container, V, the area of the packaging, A, and the Permeability, P, of the packaging material. Finally there is the %oxygen, po, in the atmosphere which is 21%

From all this, L can be calculated via the formula, with P in units of ml.mm/(m².day.atm) (i.e. the units in the guide to permeabilities), A in m², t in months, pO and q as %wt/Volume, V in ml. As with so much to do with barriers, the real challenge is the units, not the calculation. The strange 22400/32 is converting from moles to ml, with 32 being the MWt of oxygen and 22.4l being the gas molar volume. The 1000 at the top brings together all the units to provide the output in μm.

For a table of typical P values, click :

 P ml.mm/(m².day.atm) Area m² t months pO% V cc q % L μm

The app can be used in reverse. If you have a package of thickness L and want to know the shelf life, simply change the value of t till the right L emerges.