15 Oct 2025
Why do biscuits lose their crunch?
When foods absorb moisture, their glass transition temperature (Tg) drops, triggering a shift from a glassy (hard, brittle, stable) state to a plastic (soft, flexible, less stable) one. This is why crisps go soggy, or biscuits soften. Interestingly, ingredients like corn starch help raise Tg, which is why cereals or crisps can stay crunchy a bit longer even as they absorb moisture. Moisture uptake also creates preferential conditions for microbial growth, reducing both quality and shelf life.
Controlling moisture is key to texture, safety, and stability.
Through modelling and simulation, we can identify weak points and test solutions virtually, before making the first prototype.
Foods often lose their characteristic crunchiness as they absorb moisture, because the glass transition temperature (Tg) is lowered.
When this happens, a series of physical, chemical, and microbiological changes can occur, leading to reduced quality and shelf life. Crisps lose their crunch, and biscuits soften.
Moisture absorption can trigger phase transitions, shifting foods from a glassy to a plastic state at room temperature. What does this mean? In the glass phase, a food’s amorphous components are in a hard, brittle, and stable state (below Tg). When temperature rise above Tg, or enough moisture is absorbed to lower the Tg to below storage temperature, these components move into a plastic phase, becoming softer, more flexible, and less stable. Foods like dried pasta, candy, and crisps are typically in the glassy state, with low molecular mobility. Once they transition to the plastic phase, they become rubbery, sticky, and may even collapse structurally.
This phenomenon is familiar in breakfast cereals, crackers, and fried chicken. Here, starch plays a role in elevating Tg, which helps maintain crunchiness even as moisture is inevitably absorbed.
Ultimately, controlling moisture is crucial for maintaining texture, safety, and shelf stability.
Through modelling and simulation, it’s possible to identify potential problem areas and test different solutions virtually before the first prototype is created. Multiple scenarios can be simulated rapidly and cost-effectively, exploring possibilities that would be difficult or expensive to test physically.