Engineering and thermal processing

Engineers are different from scientists What do scientists do? What do engineers do? The importance of simplifying assumptions – examples

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

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

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

Thermal Processing and Refrigeration

Heating and Cooling: Heat transfer (heating or cooling) is driven by ΔT (the temperature difference) ΔT (°F) Boiling H 2 O152 Oven 350°F °F1940 Refrigerator 40°F20 Household Freezer 10°F50 Commercial Freezer -40°F100 Liquid Nitrogen -380°F440 Assume a Room Temperature of 60°F.

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

Log Numbers Time (min)# survivorsLog # survivors 11,000, , , ,

Log vs linear

Pasteurizers (Ohio State University) 60 C for thirty minutes80 C for thirty seconds

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

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

Flow Chart: Canning of Corn (FAO) Blanching!

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

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

Refrigeration and Freezing: (85 % of food is frozen at some point) Refrigeration:Freezing: Micro growthSlowStops Chemical reactionsSlowEven Slower Quality“Fresh”“Frozen” Shelf lifeShortLong Margin of errorSmall (spoilage, chill injury, cross contamination) Large Freezing: Slowly: Water migrates Freeze “pure” Solutes concentrate Large crystals Rapidly: Freezes in place No solute concentrate Small crystals Better structures

How refrigeration works Expand Energy Input Condense Simplified

Freezing: 3 Types: – Plate Freeze Contact with very cold surface – Blast Freeze Very cold air Very high velocity – Immersion N 2 Flash Frozen = “IQF”

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

“Nonthermal” processing next lecture… High pressure Irradiation UV light Pulse light High intensity light Pulsed electric field

How pumpkin pies are made… Happy Thanksgiving!