Resting biryani after the dum allows the steam to redistribute evenly, preventing a soggy bottom layer and ensuring a consistent, fluffy texture throughout. This also allows the flavors to meld and deepen.
The 'dum' cooking method involves slow cooking the biryani in a sealed pot, trapping steam inside. This steam cooks the rice and meat, infusing them with flavor. After the dum is complete, the pot contains a significant amount of residual steam and moisture. If you open the pot immediately, this steam can condense unevenly, often resulting in a soggy bottom layer of rice while the top remains relatively dry.
Resting the biryani, typically for 15-30 minutes, allows this steam to redistribute throughout the dish. The rice grains absorb the remaining moisture, leading to a more uniform texture. The flavors also continue to meld and deepen during this resting period, as the ingredients continue to interact at a lower temperature. This results in a more cohesive and flavorful biryani. Think of it like letting a cake cool before frosting; it allows the structure to set and prevents a mushy mess.
To further enhance the resting process, gently fluff the biryani with a fork before covering the pot again. This helps to separate the rice grains and allows for better steam distribution, preventing clumping and promoting a lighter, fluffier texture. Avoid stirring vigorously, as this can break the rice grains.