Revision Frying

Identify the heat transfer mode involved when heat is transferred from oil to food.

• Conduction

• Convection

• Radiation

Answer explanation

• Heat from the frying equipment (e.g., pan or fryer) is transferred to the oil. The oil then circulates heat to the food through convection currents.

  • Natural Convection: Caused by differences in temperature and density within the oil. Hot oil rises, and cooler oil sinks, creating a flow that enhances heat distribution.

  • Forced Convection: If the oil is stirred or circulated mechanically, the heat transfer rate increases due to enhanced mixing.

• Impact on Food: The outer layer of the food absorbs heat via convection from the hot oil, causing rapid temperature increases at the surface.

Why does the high boiling point of oil make it suitable as a frying medium?

• This property allows oil to transfer heat quickly and efficiently to the food, resulting in faster cooking.

• This property allows it to reach and maintain the high frying temperatures without evaporating or breaking down excessively.

• This property allows rapid heat transfer that creates a crispy exterior while sealing in the food's moisture

Answer explanation

While oil’s thermal conductivity is important for efficient heat transfer, it is secondary to its boiling point in determining its suitability as a frying medium. Without a high boiling point, the oil wouldn't sustain the temperatures needed for frying, regardless of its thermal conductivity.

Which of the following oils is suitable for deep frying?

• Coconut oil

• Corn oil

• Palm oil

Answer explanation

• Smoke Point: Approximately 230°C (446°F), making it well-suited for deep frying.

• Stability: High levels of saturated and monounsaturated fats make it resistant to oxidation and breakdown.

• Flavor: Neutral flavor that doesn't overpower the food being fried.

Which of the following fryers allows food to be fried at a lower temperature than an atmospheric fryer?

• Vacuum fryer

• Pressure fryer

Answer explanation

• In a vacuum fryer, the pressure inside the chamber is reduced to below 6.65 kPa.

• At reduced pressure, water boils and evaporates at temperatures significantly lower than the normal 100°C, which means food can be fried at lower oil temperatures (typically around 80–120°C instead of 160–190°C in conventional frying).

List three chemical reactions during frying that lead to formation of fatty acids, aldehydes and dimers

Answer explanation

Hydrolysis - due to moisture from food.

Oxidation - reaction between oxygen and lipid compounds.

Isomerization/ Polymerization - high temperature triggers the formation of degradation products