This applies to the seeds your cockatiel eats everyday.
All food will expire and perish over time, you can help reduce the speed at which this happens by storing the food in the correct way. Feed needs to be kept reasonably cool, temperatures around 10C – 12C are good to reduce condensation, do not refrigerate the food though.
The area where the food is kept should be well ventilated and not humid, if the feed is kept in a tight area for a long period of time then it will start to rot fast. Food should never be stored in direct sunlight as this will heat up the seeds causing vitamins to be less effective.
Ensure there is no vermin that can get to where you store the food, if they can you must install vermin proof methods to stop this or remove the food. Vermin can carry disease that will quickly transfer over to the feed and then over to your cockatiel.
Cockatiel food should only be kept for a few months at most, always check the expiry date on the packaging and try to buy the freshest food you can.
Any other non-seed food such as eggs and fruit need to be removed from the cage within a couple of hours of them being put there. This food will start to decompose and bacteria will grow very quickly.