To keep Nido (and any other fatty products, like Milkman, nuts, chips) from going rancid, you can either buy a vacuum sealer, a commercial oxygen scavenger packet, or take the cheap way out by using a disposable hand warmer (Hot Hands brand or similar that contain iron powder, salt, charcoal, and vermiculite). Putting one in the can will keep Nido fresh for many months. You can extend that to many years if you transfer the Nido to a clean, airtight jar. The hand warmer uses up all the oxygen so the fats can't go rancid and as a bonus, nothing that requires oxygen can grow. Opening and closing the container shouldn't cause any problem as the heat pack is designed to react with quite a bit of air - probably 50 or more containers worth. If you worry about having the pack mingle with your food, just stick it to the lid or put it inside another cloth bag.