Engineering and thermal processing

1. Engineering and thermal processing

2. Engineers are different from scientists • What do scientists do? (Technologists?) • What do engineers do? • The importance of simplifying assumptions • Examples • How long does it take to drive to Boston? • Large equipment Dimensional analysis How many inches from here to Boston?

3. Engineers deal with • Heat transfer, always runs from hot to cold so refrigerators or freezers need pumps (energy input) • Mass transfer • Mass balance • Consider a simple drier

4. The 2nd Law of Thermodynamics:everything goes to maximumrandomness (entropy) • Unless you put in energy • Electric, microwave, pressure, thermal, ionizing • Types of Heat Transfer (demo) • Conduction • Convection • Radiation

5. Most food processing involves the addition or removal of energy.Most types of food spoilage have engineering solutions.

6. Thermal Processing and Refrigeration

7. Heating and Cooling: • Heat transfer (heating or cooling) is driven by ΔT(the temperature difference) Assume a Room Temperature of 60°F.

8. Pasteurization: • 7 log kill for Salmonella in Milk = 99.99999% • Pasteurization of eggs: 3 log reduction = 99.9% 145°F for 3 to 4 mins. • Fruit juices were just heated to reduce microbial count and inactivate enzymes when they were thought not to carry pathogens. Now that pathogens have been discovered, they are pasteurized. Temperature: 145°F (63C) 161°F (72C) 212°F (100C) 280°F (131C) Time: 30 min 15 sec 0.01sec 6 sec

9. Log Numbers

10. Log vs linear

11. Pasteurizers (Ohio State University) 80 C for thirty seconds 60 C for thirty minutes

12. Canning: • Invented by Appert in 1790s. • Commercial sterility. • Destroys pathogens and spoilage organisms that can grow. • Requirements for high acid foods (pH < 4.6) are not very stringent. Why? • Can be done in a boiling water bath. Home canned tomatoes, OK Home canned beans, No

13. Requirements for low acid (pH >4.6) foods are very strict • Low acid foods pH > 4.6 • Target is C. botulinum 12 log reduction = 99.9999999999% • 2 to 4 min @ 250°F • Requires certified retort operators, approved process

14. Flow Chart: Canning of Corn (FAO) Blanching!

15. Flow Chart: Canning of Peas (FAO) Flow Chart for the pea canning process Blanching!

16. Mild vs. Severe Heat Treatment: • Mild Heat Treatment): • Aims: • Kill pathogens • Reduces bacterial load (Food is not sterile) • Inactivate enzymes • Advantages: • Minimal damage to flavor, texture, and nutritional quality. • Disadvantages: • Short shelf life • Another preservation method must be used, such as refrigeration or freezing • Examples: • Pasteurization • Blanching • Severe Heat Treatment: • Aims: • Kills all bacteria • Food will be commercially sterile • Advantages: • Long shelf life • No other preservation method is necessary • Disadvantages: • Food is over-cooked • Major changes in texture, flavor, and quality • Examples: • Canning

17. Refrigeration and Freezing:(85 % of food is frozen at some point) Freezing: • Slowly: • Water migrates • Freeze “pure” • Solutes concentrate • Large crystals • Rapidly: • Freezes in place • No solute concentrate • Small crystals • Better structures

18. How refrigeration works Simplified Energy Input Condense Expand

19. Freezing: • 3 Types: • Plate Freeze • Contact with very cold surface • Blast Freeze • Very cold air • Very high velocity • Immersion • N2 • Flash Frozen = “IQF”

20. Processing can create multiple products– Apple Juice Bottle – “hot pack” Clear glass Brown plastic Concentrate Liquid Frozen Metal can Aseptic – Brix pack (“Sipps”)

21. How pumpkin pies are made…