Heat Transfer in Food Processing

Factors Influencing Heat Transfer Rate

• Temperature difference: Larger temperature differences result in faster heat transfer.
• Surface area: Larger surface areas allow for more heat exchange.
• Thermal conductivity: Materials with higher thermal conductivity facilitate faster heat transfer.

Heat Transfer in Food Processing

• Not a food processing application: Heat transfer is used in various food processing applications, but not for food labeling.

Pasteurization in Food Processing

• Main goal: Pasteurization aims to reduce the number of microorganisms in food, increasing its shelf life and safety.

Thermal Properties

• Specific heat capacity: Represents the amount of energy required to raise the temperature of a unit mass of a substance by one degree.

Heat in Baking

• Development in baking: Heat influences gluten development, creating a structure in baked goods.

Impact of Temperature Difference

• Increased temperature difference: Leads to faster heat transfer.

Thermal Conductivity

• Units: Thermal conductivity (k) is measured in watts per meter-kelvin (W/m K).

Benefits of Understanding Heat Transfer

• Understanding heat transfer is beneficial in food processing, EXCEPT for predicting consumer preferences.

Mechanism of Heat Transfer

• Conduction: Heat is primarily transferred through molecular collisions.

Thermal Conductivity (k)

• Measurement: Thermal conductivity (k) measures the rate of heat transfer through a material under specific conditions.

Convection Coefficient (h)

• Factors influencing convection coefficient (h): Fluid velocity, fluid properties, and geometry. Not influenced by the type of food being processed.

Newton's Law of Cooling

• T∞: Represents the ambient temperature in Newton's Law of Cooling.

Emissivity (ε)

• Emissivity (ε): Defined as the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature.

Types of Heat Transfer

• Radiation: Transfers heat through electromagnetic waves.

Convective Heat Transfer

• Heating: As the fluid heats up, its density decreases, causing it to rise, creating a convection current.

Conduction vs. Convection

• Primary difference: Conduction involves heat transfer through direct contact, while convection involves heat transfer through fluid movement.

Dielectric Heating

• Primary mechanism: Dielectric heating primarily relies on polar molecules rotating in response to an alternating electric field.

Dielectric Heating Applications

• Typical food for dielectric heating: Meat.

Microwave Frequency Range

• Microwaves: Defined by a frequency range of 300 MHz to 300 GHz.

Microwave Oscillations

• Oscillations: Microwaves oscillate billions of times per second during the heating process.

Food Preservation Methods

• Not a food preservation method: Freezing.

Microwave Heating Mechanism

• Rapid heating: Microwaves' ability to directly interact with water molecules enables fast heating.

Microwave Applications in Food Processing

• Besides thawing: Microwaves are used for cooking, drying, and pasteurization.

Blanching, Pasteurization, and Sterilization

• Shared goal: To reduce microbial activity in food, improving safety and shelf life.

Blanching

• Purpose: To inactivate enzymes in food, preventing undesirable changes during preservation.

Blanching Method

• Higher nutrient loss: Steam blanching leads to higher losses of soluble nutrients compared to immersion blanching.

Sterilization

• Goal: To eliminate all microorganisms in food.

Sterilization Factors

• Time and temperature: Influenced by several factors, but NOT the thickness of the food package.

Pasteurization

• Description: A heat treatment process that kills most harmful bacteria in food while maintaining desired properties.

Pasteurization Inventor

• Inventor: Louis Pasteur

Pasteurized Foods

• Not commonly pasteurized: Meat.

Methods of Blanching

• Steam blanching: Offers faster processing time and lower water usage than immersion blanching.

Pasteurization Requirements

• Conventional pasteurization: Requires 72°C for 15 seconds.

Pasteurization Purpose

• Main purpose: To extend the shelf life of perishable foods by reducing microbial populations.

Mass Transfer Operations

• Process: involves transferring a substance from a solid material to a liquid solvent.

Mass Transfer Driving Force

• Driving force: Concentration gradient, pushing the transfer of a substance from a high concentration to a low concentration area.

Distillation

• Mechanism: Based on differences in volatility of components in a mixture, allowing their separation.