Jaggery attracts moisture inside plastic pouches due to its hygroscopic nature, meaning it readily absorbs water from the surrounding environment. The plastic pouch, while providing a barrier, isn't completely airtight and allows some moisture to permeate, which the jaggery then absorbs.
Jaggery is essentially unrefined sugar, containing molasses and various minerals. These components, particularly the molasses, are hygroscopic. This means they have a strong affinity for water molecules in the air. Even in a sealed plastic pouch, there's often some residual air and a slight permeability to moisture. Over time, water vapor from the surrounding environment can slowly seep into the pouch. The jaggery then acts like a sponge, drawing this moisture in and causing it to become sticky or even dissolve slightly. The higher the humidity of the surrounding environment, the faster this process will occur. The type of plastic used for the pouch also plays a role; some plastics are more permeable to moisture than others. Furthermore, temperature fluctuations can exacerbate the issue. Warmer temperatures increase the rate of moisture permeation and absorption.
To prevent jaggery from attracting moisture, store it in an airtight container, preferably made of glass or a high-quality, low-permeability plastic. Adding a desiccant packet (like silica gel) inside the container can also help absorb excess moisture and prolong its shelf life.