This kind of "was not to be eaten" is a part of "be to infinitive" usage. It has many usages such as obligation, possibility, schedule, etc. Some grammar books say this kind of passive voice of "be to infinitive" as a complement usually denotes possbility, but this example seems to be an obligation.
What do you think? Does it all depend on context to determine its usage?
ex) Immediately after World War II, the allied armies gathered up many hungry and homeless children and placed them in large camps. In these camps, they fed and took care of the children. However, at night the children did not sleep well; they seemed restless and afraid. Finally, a psychologist hit upon a solution. When the children were put to bed, they would receive a slice of bread to hold. If they wanted more to eat, more was provided, but this special slice was not to be eaten — it was just to hold. The slice of bread produced wonderful results.The children went to sleep, feeling that they would have something to eat tomorrow, and that assurance gave the children a calm and peaceful rest.
Last edited by keannu; 07-Nov-2012 at 00:53.
Last edited by bhaisahab; 07-Nov-2012 at 10:10. Reason: correction
You mean the expression is like usage of "purpose or use" such as "This certificate is to certify this individual as the..."? It might have been possible just to give them inedible bread for an edible one the next morning.