A twin-screw extruder conveys a protein/water dough through a heated barrel and then a cooled, narrowing die. Two competing effects set the final texture: shear-induced alignment of unfolded protein strands, and thermal relaxation that randomizes them again.
Shear rate: γ̇ = π·D·N / δ
Consistency: K(T) = K0 · exp[Ea/R · (1/T − 1/T0)] (Arrhenius, shear-thinning)
Alignment ODE: dS/dt = α·γ̇·(1−S) − S/τ(T), τ(T) = τ0·exp[−β(T−T0)]
Steady value: S_ss = α·γ̇·τ / (1 + α·γ̇·τ)
- Screw speed (N) — raises γ̇ linearly, driving more alignment and more viscous heating (higher SME).
- Cook temperature (T) — needed to denature and mobilize the protein network, but too hot shortens τ(T) and lets strands relax back to a disordered mush before they reach the die.
- Moisture — lowers the melt's consistency K, trading some alignment for a softer, less energy-intensive melt (the HMEC "high-moisture" regime, 50–75%, is what yields a meat-like rather than crunchy TVP texture).
- Cooling-die temperature — the die is a long, narrowing, water-cooled channel. A colder die quenches the melt fast enough to freeze whatever alignment the cook zone produced; a warm die lets it relax and the fibers blur back out before solidifying.
Real-world relevance: this is the mechanism behind plant-based "meat" — Beyond Meat, Impossible Foods and most alt-protein manufacturers run exactly this cook-then-quench sequence in a twin-screw extruder to turn isotropic soy/pea protein into anisotropic muscle-like fiber, without any animal tissue.