Masala boxes are better with metal lids. Metal lids block light and air, preserving the spices' flavor and aroma for longer.
The primary function of a masala box is to protect spices from factors that degrade their quality, such as light, air, and moisture. Metal lids excel at this because they are opaque, preventing light from reaching the spices. Light can cause spices to lose their color and flavor over time. Metal lids also create a tighter seal than glass lids, reducing air exposure. Air can oxidize spices, leading to a loss of potency and flavor. While glass lids allow you to see the spices inside without opening the box, this benefit is outweighed by the superior preservation offered by metal lids. Some masala boxes come with an inner lid for each spice container, further enhancing preservation.
To further protect your spices, store your masala box in a cool, dark, and dry place, away from direct sunlight and heat sources like the stove. This will help maintain their freshness and flavor for an extended period.