Year 10 Science · Unit 2 · Lesson 17

Chemical Reactions in Everyday Life

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Learning Goals

Trace the because-chain from egg heat to denaturation to Maillard browning.
Identify multiple reaction types operating simultaneously in sourdough bread.
Apply the concept of reaction type classification to complex, real cooking scenarios.

Warm Up

Because… chain

Fill in the missing effects. The first and last steps are given, complete the four missing effects in the chain.

An egg is placed in boiling water at 100°C

→

Heat energy is absorbed by egg protein molecules

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Protein bonds break and the protein unfolds (denatures)

→

If the egg is fried (surface >140°C), amino acids react with sugars

→

New flavour compounds form at the browned surface

→

Maillard reaction produces brown colour and complex aroma

Overall outcome:

Your Turn

Real-world context

Bakers at Bourke Street Bakery in Sydney use a sourdough starter that has been maintained for over 20 years. As the dough rises, wild yeast converts glucose into ethanol and CO₂ (fermentation), lactic acid bacteria produce lactic and acetic acids (giving the sour taste), and the CO₂ gas is trapped in the gluten network, causing the dough to expand. When baked above 200°C, the crust undergoes the Maillard reaction, turning golden-brown and developing its characteristic crisp texture and roasted flavour.

(a) Identify three distinct chemical reaction types that occur during the making of sourdough bread from this description. For each, name the reaction type and the chemical change involved.

Apply 3 marks

(b) Classify each of your three reactions as endothermic or exothermic. Justify your answers.

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Wrap Up

In one sentence, explain why the Maillard reaction only occurs on the crust of bread and not in the soft interior during baking.