Fundamental of Food engineering

These question-and-answer flashcards review all key principles introduced in the Week 5 lecture on food engineering: definitions, safety drivers, canning, pasteurisation, units, mass & energy balances, heat and fluid dynamics, non-Newtonian behaviour, unit operations, and real-world examples such as milk processing. Designed for rapid revision before exams.

What is the primary goal of food engineering?

To apply scientific, technological and mathematical principles to convert raw ingredients into safe, desirable food products.

In food engineering, what four key stages are considered after raw material acquisition?

Processing, packaging, storage and distribution.

Why is safety the number-one priority in any food process?

Unsafe food endangers consumers and ultimately prevents companies from profiting; food must be safe before it can be sold.

Define pasteurisation for milk in Australia (standard HTST).

Heating milk to 72 °C for 15 seconds to destroy pathogenic microorganisms.

Which microorganism is specifically targeted in commercial can sterilisation?

Clostridium botulinum.

What is the ‘botulinum cook’ condition used for low-acid canned foods?

121.1 °C (250 °F) for 2.88 minutes inside a pressurised retort.

Why is 121.1 °C used instead of 121 °C?

It is the precise metric equivalent of 250 °F; even 0.1 °C matters in lethality calculations.

Approximately how much botulinum toxin (in nanograms) can be lethal to humans?

~30 nanograms (≈1⁄1000 of a grain of salt).

List the three modes of heat transfer.

Conduction, convection and radiation.

In heat transfer, which direction does heat always move?

From the hotter object/region to the colder one (never ‘cold’ to hot).

What is a plate heat exchanger used for in dairy processing?

Rapidly heating (or cooling) milk by transferring heat across many thin plates with a large surface area.

Explain the term ‘cold chain’.

A temperature-controlled supply chain that keeps foods refrigerated from production to consumer to slow microbial growth.

How long can correctly processed canned food remain microbiologically safe?

Indefinitely, provided the can seam stays intact and the heat treatment was sufficient.

Name the three fundamental SI base units most common in engineering.

Kilogram (mass), metre (length) and second (time).

What aviation incident highlighted the danger of mixing unit systems?

The 1983 Gimli Glider, caused by calculating fuel in pounds instead of kilograms.

State the law of conservation of mass in process engineering terms.

Total mass entering a system equals total mass leaving (including accumulation) – mass can’t be created or destroyed.

State the law of conservation of energy relevant to food processes.

Energy cannot be created or destroyed; it is only converted from one form to another within the process.

What is a mass balance used for?

To account for all material entering, leaving and accumulating in each unit operation or an entire plant.

Define viscosity.

A fluid’s resistance to deformation or flow; informally, how ‘thick’ it is.

Give one example of a Newtonian food fluid.

Water (also milk, dilute sugar syrup, etc.).

Give one example of a shear-thinning (pseudoplastic) food.

Tomato ketchup/sauce (others: yoghurt, mayonnaise).

Give one example of a shear-thickening (dilatant) system used in demonstrations.

Corn-starch slurry (oobleck).

What type of non-Newtonian behaviour does peanut butter exhibit?

Bingham (yield-stress) behaviour – it doesn’t flow until a critical stress is exceeded.

Which dimensionless number predicts laminar vs turbulent flow?

The Reynolds number (Re).

How does flow regime affect mixing?

Laminar flow gives minimal mixing; turbulent flow promotes intense mixing and uniformity.

List four common unit operations in food factories.

Heating, cooling, mixing, separation (others: drying, evaporation, packaging…).

What equipment is commonly used to separate cream from skim milk?

A high-speed centrifugal separator (cream separator).

Why is drying an effective preservation method?

It lowers water activity, inhibiting microbial growth and many spoilage reactions.

Name two industrial drying technologies.

Hot-air tunnel dryer and freeze dryer (lyophiliser).

What advantage does freeze-drying have over conventional drying?

It removes water at low temperature by sublimation, better preserving nutrients, colour and structure.

What is the function of a blast chiller?

Rapidly removing heat from food by high-velocity cold air to pass quickly through the temperature danger zone.

Describe a double seam in canning.

Two interlocked folds of the can end and body rolled together to create an airtight hermetic seal.

Which high-pressure alternative to heat pasteurisation is growing in popularity?

High-Pressure Processing (HPP).

Why is HPP milk much more expensive than HTST milk?

The extremely high pressures (≈600 MPa) require costly equipment and energy.

What legal change is required on allergen labels for ‘tree nuts’?

They must specify the exact nut(s) (e.g., almond, hazelnut) rather than the generic term ‘tree nuts’.

Give two reasons for food processing other than safety.

Extending shelf life, creating new textures/flavours, increasing variety, enhancing nutrition, adding value.

What does UHT stand for and how long can UHT milk last unopened at room temperature?

Ultra-High-Temperature; up to ≈6 months.

Which three factors in the Reynolds equation can a food engineer adjust to change flow regime?

Fluid velocity, viscosity, and pipe diameter (fluid density is usually fixed).

Give one environmental concern linked to food packaging.

Excessive plastic use leading to long-term waste and pollution.

Name four common packaging materials.

Paper/paperboard, plastic, aluminium (foil/cans), glass (plus composites of these).

What is meant by ‘unit operation’?

An individual, fundamental processing step (e.g., mixing, heating, drying) performed in a specific piece of equipment.

Which operation turns dilute tomato purée into thick paste?

Evaporation (water removal under heat and/or vacuum).

Why should flow of starch slurry be kept relatively slow in pipes?

Fast shear causes shear-thickening, raising viscosity and risking pipe blockage.

In a plate heat exchanger, why are many thin plates preferred?

They create a huge surface area and thin film thickness, enabling rapid heat transfer.

How does low temperature slow microbial growth?

It decreases reaction rates, prolonging the lag phase and reducing reproduction speed of microorganisms.

Why doesn’t canned food need an expiry date but usually shows ‘best before’?

Correctly processed cans are microbiologically stable indefinitely, yet flavour, colour or texture may deteriorate over time.

How does a centrifuge exploit density differences?

Rotational forces push denser components outward, allowing lighter components to separate toward the axis.

What is the purpose of a continuous oven in biscuit production?

To heat every biscuit for the same time/temperature as they travel on a conveyor, ensuring uniform colour and moisture.

Highlight two benefits of turbulent flow in a food pipeline.

Enhanced heat transfer and better mixing (avoids temperature or concentration gradients).

Summarise the milk processing chain from farm to consumer in three critical steps.

Cold storage at farm, pasteurisation (or UHT) at factory, continuous refrigeration through distribution and retail.