Vacuum pre-cooling is exceptionally fast and energy efficient for lettuce and leafy vegetables because:
Options:
(A) Leafy vegetables have a very high ratio of surface area to mass, permitting rapid boiling of surface water at low absolute pressures ($0.8\text{ kPa}$)
(B) Vacuum destroys all cell walls allowing thermal radiation to escape instantly
(C) Air conduction increases by ten-fold in a high vacuum
(D) Vacuum cooling freezes the food solid within 5 seconds
Answer Key:
A
Step-by-Step Solution & Explanation
Vacuum cooling lowers chamber pressure to the saturation vapor pressure of water at the desired cold temperature (e.g., $0.81\text{ kPa}$ for $4^\circ\text{C}$). Water boils flash-evaporatively, drawing the latent heat of vaporization ($2500\text{ kJ/kg}$) directly from the vegetable tissue.