The effect of heat on food

    OCR
    GCSE

    The study of heat transfer and its physicochemical effects on food is central to Food Preparation and Nutrition. Candidates must understand the three mechanisms of heat transfer—conduction, convection, and radiation—and apply this physics to culinary practice. Crucially, this topic covers the functional chemical changes induced by thermal energy: protein denaturation and coagulation, carbohydrate gelatinisation, dextrinisation, and caramelisation, as well as the emulsification and plasticity of fats. Assessment focuses on the scientific principles underlying these changes (AO1), the selection of appropriate cooking methods for specific ingredients (AO2), and the evaluation of how heat impacts nutritional value, sensory qualities, and food safety (AO4).

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    Objectives
    4
    Exam Tips
    3
    Pitfalls
    3
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award marks for accurate scientific terminology: 'polysaccharide chains', 'glycosidic bonds', or 'protein unfolding' rather than generic terms like 'breaking down'.
    • Credit responses that distinguish clearly between coagulation (setting/solidifying) and denaturation (structural alteration) in protein-based contexts.
    • Candidates must quantify critical temperatures: gelatinisation initiation at 60°C, completion at 100°C; caramelisation of sucrose at 160°C-170°C.
    • Reward application of knowledge: explaining defects such as syneresis (over-coagulation) or lumps in sauces (insufficient agitation during gelatinisation).

    Marking Points

    Key points examiners look for in your answers

    • Award marks for accurate scientific terminology: 'polysaccharide chains', 'glycosidic bonds', or 'protein unfolding' rather than generic terms like 'breaking down'.
    • Credit responses that distinguish clearly between coagulation (setting/solidifying) and denaturation (structural alteration) in protein-based contexts.
    • Candidates must quantify critical temperatures: gelatinisation initiation at 60°C, completion at 100°C; caramelisation of sucrose at 160°C-170°C.
    • Reward application of knowledge: explaining defects such as syneresis (over-coagulation) or lumps in sauces (insufficient agitation during gelatinisation).

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When discussing gelatinisation, structure the answer chronologically: suspension -> swelling (60°C) -> bursting (80°C) -> gelatinisation (100°C).
    • 💡For 'Evaluate' questions on cooking methods, contrast nutritional loss (water-soluble vitamins) against sensory improvement (Maillard reaction).
    • 💡Use the 'Statement -> Explanation -> Example' structure for 6-8 mark questions to ensure AO2 application marks are secured.
    • 💡Memorise the specific critical temperatures for egg proteins: whites coagulate at 60°C, yolks at 70°C; use this to explain syneresis.

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing dextrinisation (dry heat on starch) with caramelisation (dry heat on sugar).
    • Stating that proteins 'die' or 'kill bacteria' as the primary chemical change, rather than 'denature' and 'coagulate'.
    • Failing to identify that enzymes are proteins and therefore susceptible to denaturation by heat and pH extremes.

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    State
    Describe
    Explain
    Discuss
    Evaluate
    Analyse

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