My physic teacher told a story where he bought some beef, put them into a vacuum (separated), measured their weight and put them into the freezer. Some days later he wanted to cook one of them but he couldn't see a difference between the beefs and his other meats. So he decided to weight them since he wrote their weight down before. Surprisingly none of them had one of the noted weights, he told that they were completely different. His biggest beef weighed about 1.300g but now it weigh less (I can't remember the number anymore).
What's your question?
What could be the reasons that the beefs lost their weights, although they were packed in a vacuum and put into a freezer?