A foil pouch of dal sits on a shelf for a year and is edible when opened. The processing that makes this possible is closer to canning than to anything a kitchen does.
The food is sterilized inside the sealed package
The pouch is filled, sealed, and then heated in a pressurized vessel called a retort, which raises the contents above the boiling point of water.
Because the package is already closed, nothing can recontaminate the food afterward. The seal is the barrier and the heat treatment is what makes the interior stable.
This is the same principle as a can, applied to a laminated flexible pouch that heats faster because the food sits in a thinner layer.
Shape is why pouches beat cans here
A thin pouch reaches processing temperature throughout in much less time than a cylindrical can, so the food spends fewer minutes being overcooked at the edges.
That shorter exposure preserves more texture and color, which matters for dishes with visible pieces of vegetable or meat rather than a uniform puree.
The laminate also includes a metal layer that blocks light and oxygen, so the barrier performance is close to a can at a fraction of the weight.
Some dishes survive the process better than others
Gravies and pulses come through well, since they are already soft and cooked through and the extra heat changes little.
Anything meant to be crisp, fresh or brightly herbal does not, which is why the category is built on curries and rice rather than on fried snacks or salads.
Spice profiles are often adjusted for the process too, because volatile aromatics are driven off by the heat and the finished pouch would otherwise taste flat.
Preservatives are not what is doing the work
Shoppers frequently assume a long shelf life implies heavy chemical preservation, when the stability comes from the seal and the thermal treatment instead.
Labels bear this out, since many pouches list only the ingredients of the dish, and the salt levels that draw comment are there for flavor rather than for keeping.
The seal is the vulnerable part instead, which is why a pouch that has been punctured or has swollen should be discarded rather than opened and judged by smell.
Why the format spread beyond India
The pouches travel well and need no refrigeration in transit, which suits export and puts regional dishes on shelves far from any kitchen that would cook them.
They also fit how many people actually eat, adding a cooked component to a home-made one rather than replacing the meal, which is a lower bar than a frozen entree faces.
For an American shopper the practical use is often a base, since a pouch of gravy stretched with fresh vegetables becomes a larger dish than the package suggests.