The temperature 121°C is needed for retorting the non-acidic or less acidic food.
The extreme temperature at which microorganism or bacteria presence in the foodstuffs are found in a large number stint is called the ‘spore state’. Bacteria can be grown n in less acidic or non-acidic substance at a spore state. That is why after scaling, these foodstuffs are retorting at temperature 121°C. Because 121°C is that temperature at which the spore of bacteria have to be broken down.