Moisture and oxygen will spoil foods and cause them to oxidize. Since the moisture content of freeze-dried and dehydrated foods is very low, the risk of spoilage by moisture is very low. But the oxygen in the pouch must be replaced. This is done by first evacuating the pouch and then filling it with pure nitrogen before it is sealed. Nitrogen accounts for about 79 % of the air we breathe and is entirely safe for foods.