Dear Sumaviab,
I would like to share the little I know regarding the classification of Pathu in the kitchen.
If we look at it, our food intake has enormous effect on our thought process. Naturally, we would like to keep our thought process at the peak as far as possible. The practise of Pathu has been introduced ages before only to bifurcate those food items which can be taken and those which should be thrown away. Here only the concept of Pathu comes in. The vessel we use, the combination of cereals, pulses, vegetables, etc we use to prepare the dish and the retention period, say a few hours or a day, has a lot of implications to contaminate without loss of taste. Hence, those items which are prepared, for example, sweets, will last longer than those prepared with salt. Here the essence is the time factor of how many hours the item has been kept without consumption. With this parameter, whether we are in the midst of a truly brahmin agraharam or in the most modern part of the globe we can identify items which are Pathu and which are not. Believe me, this has helped me wherever I was preparing my own food when staying in any country for months together.
It is important that we should not bring in the petty economy of storing something to save a few pennies but attract indirect pulling physical and mental disturbances. In case we come to know of any new guideline regarding Pathu we can go deep within ourselves and try to understand whether it holds any relevance. If yes we can accept it or set aside as one more belief. We can be confident this way as we should be religious and not superstitious.
I hope my little thoughts can open many windows in your mind as we all are seekers after perfection which is the ever eluding goal post.