Agricultural/Bioengineering Agricultural/Bioengineering: Dairy Engineering 5

Question 1

What is the thermodynamic purpose of using a multi-effect evaporator rather than a single-effect evaporator for milk concentration?

Accepted Answer

Each additional effect uses the vapor from the preceding effect as heating steam, dramatically reducing total steam consumption per kg of water evaporated

Answer

In a multi-effect evaporator, vapor generated in effect 1 serves as heating medium in effect 2 (at lower pressure/temperature), so a 5-effect unit requires only ~1/5 the steam of a single-effect unit for equal evaporation.

Question 2

During Cheddar cheese aging, what biochemical reaction is primarily responsible for the development of sharp flavor notes?

Accepted Answer

Proteolysis by residual rennet and starter enzymes releasing bitter peptides and free amino acids

Answer

Proteolysis breaks down casein into peptides and free amino acids; further catabolism produces volatile compounds (e.g., short-chain fatty acids, sulfur compounds) that define sharp Cheddar flavor.

Question 3

What is the function of the flow diversion valve (FDV) in an HTST pasteurization system?

Accepted Answer

It diverts under-pasteurized milk back to the raw milk balance tank if the required holding temperature is not achieved

Answer

The FDV is a safety device that continuously monitors holding tube temperature and automatically diverts forward flow back to the raw side if temperature falls below the legal minimum (72°C/15 s).

Question 4

In whey protein concentrate (WPC) production, what role does ultrafiltration (UF) play?

Accepted Answer

UF removes lactose and minerals through the membrane while retaining whey proteins in the retentate

Answer

UF membranes (~10 kDa MWCO) retain whey proteins (β-lactoglobulin, α-lactalbumin, ~15–18 kDa) in the retentate while lactose, salts, and water permeate, producing WPC80 at ~80% protein on a dry basis.

Question 5

A dairy engineer is designing the holding tube for an HTST system. If the legal minimum hold time is 15 seconds and the pump delivers milk at 20 L/min, what minimum tube volume is required?

Accepted Answer

5.0 liters

Answer

Volume = flow rate × time = (20 L/min) × (15 s ÷ 60 s/min) = 5.0 L; the tube must hold at least 5.0 L to guarantee every particle is held for 15 seconds.

Agricultural/Bioengineering Practice Test

Agricultural/Bioengineering Practice Test

Agricultural/Bioengineering Agricultural/Bioengineering: Dairy Engineering 5