Roasted curry leaves become brittle quickly due to the loss of moisture during the roasting process. The heat evaporates the water content, leaving them dry and fragile.
Curry leaves naturally contain a significant amount of moisture. When you roast them, whether in a pan, oven, or microwave, this moisture evaporates. The cell structure of the leaf, which relies on water for its flexibility, collapses as the water is removed. This results in the leaves becoming dry, brittle, and easily crumbled. The extent of brittleness depends on the roasting time and temperature; longer roasting at higher temperatures will lead to quicker and more pronounced brittleness. Furthermore, the natural oils within the curry leaves, which contribute to their aroma and flavor, can also volatilize during roasting, further contributing to the change in texture. The lack of moisture and the alteration of the leaf's structural integrity are the primary reasons for the rapid embrittlement of roasted curry leaves.
To prevent curry leaves from becoming overly brittle and losing too much flavor, roast them at a low temperature for a shorter duration. Keep a close eye on them and remove them from the heat as soon as they become fragrant and slightly crisp, but before they turn completely brittle.