You have raised a subject that most people don't ever need to consider, but I have come across this problem a number of times in powders (especially low fat).
There are a number of packaging items around the world that have "Microperf Holes" in them to get rid of the air. This is not desirable with long shelf life products, but for short shelf life or very stable products, can be acheived a number of ways;
a) Pin holes punched in the film during manufacture or packing, using rollers with pins or a machinal pin.
b) Laser holes cut into the film again duing the film manufacture or packing point.
c) Air paths in fin seals for form fill seal packs. These are often proprietry designs, but there are a few vendors out there that may advise on how to do this.
But best of all is to understand why there is air (or too much gas) in the pack and how to get it out prior to, or at the sealing stage of the packing line.
Also consider if you may have a static electricity issue with the product, with either a positive or negative charge! If the packs dont feel full of air after sealing but do so after 4 or 5 days later, then this could be caused by the charged product particals pushing each other away, like magnets pushing each other. The charge needs to be released in the product before sealing the bags.
Hope this helps.
Cheers
Peter
