Crispness Phase Diagram

Place a specimen at a chosen storage humidity, run moisture uptake forward in time, and read the stability margin before it crosses from glassy and crisp into rubbery and softened.

This instrument implements the temperature–moisture state diagram from Module 9 and Module 11, and is the central figure of the lecture Crispness Is a Metastable State. Choose a specimen and a storage relative humidity, then advance time to watch its moisture content climb toward that humidity's equilibrium value and its state slide across the diagram. The stability margin — how long it takes to cross from glassy into rubbery at ambient temperature — is read directly off the same crossing the moisture-uptake plot marks.

Close-up of a crispy fried crust texture — Specimen — glassy fractureA crisp material is a frozen liquid. Below its glass transition a starchy crust fractures instead of bending — every fracture is a crack propagating through a metastable solid.

State diagram — temperature (°C) vs moisture content w₂ (mass fraction)

Moisture uptake — moisture content w₂ vs time (hours since cooking)

Glassy — crisp region
Rubbery — softened region
Glass-transition curve T_g(w₂)
Specimen's initial state
Specimen's current state
Stability-margin crossing

Current state

Specimen comparison at this humidity

Stability margin for each specimen, all evaluated at the humidity set above.

Specimen	Stability margin

References

Gordon, M. & Taylor, J.S. (1952). "Ideal Copolymers and the Second-Order Transitions of Synthetic Rubbers. I. Non-Crystalline Copolymers." Journal of Applied Chemistry 2(9), 493–500.
Roos, Y.H. Phase Transitions in Foods, 2nd ed. Academic Press.
Williams, M.L., Landel, R.F. & Ferry, J.D. (1955). "The Temperature Dependence of Relaxation Mechanisms in Amorphous Polymers and Other Glass-Forming Liquids." Journal of the American Chemical Society 77(14), 3701–3707.