Agricultural/Bioengineering Food Processing Unit Operation 3

Question 1

Which unit operation best describes the removal of alcohol from fermented beer using a vacuum and gentle heat?

Accepted Answer

Vacuum stripping (thin-film evaporation)

Answer

Vacuum stripping or thin-film evaporation lowers the boiling point of ethanol, allowing gentle removal with minimal flavor loss.

Question 2

The HTST (High Temperature Short Time) pasteurization condition for fluid milk in the US is:

Accepted Answer

72°C for 15 seconds

Answer

US FDA mandates HTST pasteurization at a minimum of 72°C (161°F) for at least 15 seconds to eliminate pathogens including Coxiella burnetii.

Question 3

In extrusion cooking of breakfast cereals, the die pressure primarily controls:

Accepted Answer

Product expansion ratio and texture after exiting the die

Answer

Die pressure determines the degree of flash evaporation and starch expansion upon exiting, directly controlling puff texture and bulk density.

Question 4

Membrane filtration processes are ranked by pore size from largest to smallest as:

Accepted Answer

Microfiltration → Ultrafiltration → Nanofiltration → Reverse Osmosis

Answer

MF has the largest pores (~0.1–10 µm), followed by UF (~0.001–0.1 µm), NF (~0.001 µm), and RO which rejects nearly all solutes.

Question 5

In a spray drier, atomization of the feed liquid is performed to:

Accepted Answer

Maximize surface area-to-volume ratio for rapid moisture evaporation

Answer

Atomization creates millions of tiny droplets with enormous surface area, allowing water to evaporate within seconds even at moderate temperatures.

Agricultural/Bioengineering Practice Test