Biryani masala powder is a blend of whole spices roasted and powdered. This spice blend not only adds the unique flavour but also lends the aroma that's required for a perfect biryani.
Roast spices just until fragrant and ensure spices do not change the colour.
Roast the spices on medium low flame to avoid over roasting or burning the spices. Keep stirring frequently.
Biryani masala powder remains fresh for 2 months, later it looses its aroma gradually. I would suggest to make masala in small batches.