Leftover rice is handled more cautiously in food safety guidance than most leftovers, and the reason is specific to the grain rather than to rice dishes in general.
Why cooking does not fully sterilise it
Certain bacteria commonly present on grains form spores, a dormant structure far more resistant to heat than the active organism. Boiling does not reliably destroy them.
The spores survive the pot and remain in the cooked rice. On their own they cause no problem while the food stays hot or is eaten promptly.
The concern arises when the rice sits at a temperature where those spores can return to active growth.
The window that matters is the cooling one
Between roughly fridge temperature and serving heat lies a band in which bacterial growth proceeds quickly. Time spent in that band is what accumulates risk.
A large covered pot of rice cools slowly, because the mass is dense and the centre is insulated by everything around it. It can remain in that band for hours.
Spreading rice thin, using shallow containers and refrigerating promptly all work by shortening the same interval.
Why reheating is not the fix
Some of the toxins produced during growth are themselves heat stable, so reheating can kill the bacteria without removing what they produced.
This is the point that surprises people, since reheating is intuitively treated as a reset. For this particular hazard it is not one.
Guidance therefore concentrates on how quickly the rice was cooled and how long it has been stored rather than on how hot it is served.
How traditional kitchens handled it
Households that cooked rice fresh for each meal never accumulated the problem, and cooking to the meal rather than to the week was the norm in most Indian kitchens.
Where rice was kept, it was often held under water overnight and fermented deliberately, which produces an acidic environment quite different from a sealed container of plain rice.
Those practices sit outside modern refrigeration but address the same underlying issue by not leaving cooked grain sitting neutral and warm.
What this means for batch cooking
Cooking rice in quantity is entirely workable, but the cooling step needs to be planned rather than left to happen. That means portioning immediately rather than after the pot has stood.
Dishes where rice is mixed with acidic or heavily spiced components behave somewhat differently, though the same cooling principle still applies.
Specific storage times and temperatures are published by national food safety authorities and vary between countries, so those are the sources worth following rather than general rules of thumb.