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

Multi-effect units operate at higher temperatures to achieve faster evaporation rates

Answer

Multi-effect systems allow simultaneous processing of different milk products in each effect

Answer

Multi-effect units eliminate the need for a condenser by venting vapor to atmosphere

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

Oxidation of unsaturated fatty acids producing aldehydes and ketones

Answer

Lactose fermentation continuing in the curd producing excess lactic acid

Answer

Maillard reactions between lactose and lysine residues at ambient aging temperatures

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

It controls the flow rate of milk through the regeneration section to maintain pressure balance

Answer

It regulates steam pressure to the heating section to prevent overheating of the milk

Answer

It separates cream from skim milk when the system detects a fat content deviation

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 separates fat from whey by applying pressure across a 1 µm membrane

Answer

UF pasteurizes the liquid whey by heating the feed under transmembrane pressure

Answer

UF crystallizes whey proteins by reducing temperature during filtration

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

3.0 liters

Answer

0.33 liters

Answer

300 liters

Question 6

What is the primary reason that whey protein denaturation during milk pre-heat treatment (e.g., 90°C/5 min for yogurt) improves yogurt texture?

Accepted Answer

Denatured β-lactoglobulin associates with κ-casein on micelle surfaces, increasing water-holding capacity and gel firmness

Answer

Denatured whey proteins precipitate out, increasing the total solids content of the serum phase

Answer

Heat treatment at 90°C sterilizes the milk, reducing competition for starter culture bacteria

Answer

Whey protein denaturation increases the lactose content available for fermentation

Question 7

In the context of milk powder production, what is meant by 'instant' or 'agglomerated' powder and why is it produced?

Accepted Answer

Instant powder consists of porous clusters of primary particles produced by rewetting and re-drying, improving wettability and dispersibility in water

Answer

Instant powder has a reduced particle size (<10 µm) for faster dissolution, produced by additional milling after spray drying

Answer

Instant powder is heat-treated after drying to denature proteins for improved beverage stability when reconstituted

Answer

Instant powder has added emulsifiers coated onto primary particles to reduce surface tension during reconstitution