Question 1 If prasadam is spiritual why does it decay like normal food does in a day or so?
Answer by Romapada Swami: Prasadam is spiritualized by virtue of its contact with the Supreme Lord. Prabhupada gives the example of iron rod and fire. The iron rod kept in fire acts like fire, but is not fire itself. Prasadam is spiritual in that it has been accepted by Krishna, and thus it has a spiritualizing effect on those who partake of it. Nevertheless, it is still made of material elements and appears to our mundane vision as undergoing material transformations. The same applies to the deity forms of the Lord (archa-vigraha), the body of a pure devotee, the holy dhama (place of pilgrimage) and the sacred scriptures.
An advanced devotee, however, would be able to see the actual spiritual nature of each of these items, and would never consider them according to their material appearance, just as Raghunatha dasa Gosvami was accepting old and spoiled remnants of Jagannath maha prasadam as delightful mercy of Lord Jagannath.
Question 2: Some devotees insist that, while taking prasadam, only those who have not eaten can serve; they say that those who have just eaten are unclean. How can one be unclean while taking in prasadam? One added point is that if we were to be taking prasadam in a house where we would like to have all of the family members honor prasadam simultaneously, it would not be possible to do so if we insisted on the above rule.
Answer by Romapada Swami: The general principle is that after eating, one must at least wash one’s mouth, hands and feet, before touching other things, especially kitchen utensils which are used in Krishna’s service (like serving utensils). Although prasadam is transcendental and purifying, while eating our hands touch our mouth (either directly or with a spoon or fork), which is not clean. The minimum Vedic standard of cleanliness we should follow after eating is that we must cleanse our hands and mouth thoroughly. Prior to worship of an installed Deity in the Temple, one must fully bathe and put on a clean set of clothes after eating.