Agricultural/Bioengineering Agricultural/Bioengineering: Dairy Engineering 2 — Questions and Answers
Question 1: What is the primary purpose of homogenization in fluid milk processing?
- To pasteurize milk by applying pressure
- To reduce fat globule size and prevent cream separation (Correct answer)
- To increase protein content through mechanical shearing
- To remove bacterial spores by high-pressure filtration
Correct answer: To reduce fat globule size and prevent cream separation
Homogenization forces milk through a small orifice under high pressure, reducing fat globule diameter from ~4 µm to <1 µm so cream cannot rise.
Question 2: In a plate heat exchanger used for milk pasteurization, what does the regeneration section accomplish?
- It heats raw milk using steam from a boiler
- It pre-heats incoming cold raw milk using hot outgoing pasteurized milk (Correct answer)
- It cools pasteurized milk using chilled water
- It sterilizes the plates between batches using caustic solution
Correct answer: It pre-heats incoming cold raw milk using hot outgoing pasteurized milk
The regeneration section transfers heat from hot pasteurized milk to incoming cold raw milk, improving overall energy efficiency by up to 90%.
Question 3: A dairy plant measures the brix value of whey concentrate at 60°. What is this measurement primarily indicating?
- Fat percentage by weight
- Total dissolved solids expressed as equivalent sucrose percentage (Correct answer)
- Protein content determined by refractometry
- Lactose crystallization onset temperature
Correct answer: Total dissolved solids expressed as equivalent sucrose percentage
Brix refractometry measures the refractive index and reports total dissolved solids as if they were sucrose, giving a practical concentration proxy for whey processing.
Question 4: What does the term 'somatic cell count' (SCC) in raw milk primarily indicate?
- The number of lactic acid bacteria per mL
- The concentration of casein micelles per mL
- The level of udder inflammation and mastitis presence in the herd (Correct answer)
- The degree of fat globule clustering measured by microscopy
Correct answer: The level of udder inflammation and mastitis presence in the herd
SCC reflects the number of white blood cells shed into milk; elevated counts (>200,000 cells/mL) signal mastitis and reduced milk quality.
Question 5: Which membrane separation process is most appropriate for concentrating casein micelles while passing lactose and whey proteins through?
- Reverse osmosis (RO)
- Nanofiltration (NF)
- Microfiltration (MF) (Correct answer)
- Electrodialysis
Correct answer: Microfiltration (MF)
Microfiltration (0.1–0.2 µm pore size) retains casein micelles (~0.1–0.3 µm) while allowing lactose, minerals, and whey proteins to permeate.
Question 6: In cheese manufacturing, what is the role of calcium chloride (CaCl₂) addition to pasteurized milk?
- It lowers pH to accelerate acid coagulation
- It restores calcium ions lost during pasteurization to improve rennet coagulation (Correct answer)
- It acts as a preservative against spoilage bacteria
- It increases the fat content to meet legal standards
Correct answer: It restores calcium ions lost during pasteurization to improve rennet coagulation
Pasteurization reduces soluble calcium, weakening the casein micelle network; CaCl₂ addition restores ionic calcium and improves gel firmness and curd yield.
Question 7: A spray dryer producing whole milk powder operates with an inlet air temperature of 180°C and an outlet of 80°C. What is the primary reason outlet temperature is kept below 100°C?
- To prevent Maillard browning and heat damage to lactose and proteins (Correct answer)
- To reduce energy costs by limiting steam consumption
- To maintain positive pressure inside the drying chamber
- To ensure the powder is at equilibrium moisture content above 8%
Correct answer: To prevent Maillard browning and heat damage to lactose and proteins
Outlet temperatures above ~100°C accelerate Maillard reactions between lactose and proteins, causing browning, off-flavors, and reduced solubility of the powder.
Agricultural/Bioengineering Agricultural/Bioengineering: Dairy Engineering 2
What is the primary purpose of homogenization in fluid milk processing?