Cooking and Chemistry

1
Cooking and Chemistry

• Read through these slides
• there may be some simple activities for you to
  try
• Happy revising!
• Mr. Smith, April 2010

2
The Chemistry of Cooking

• MUST know why food is cooked
• SHOULD know cooking is a chemical reaction
• COULD describe the structures of proteins

3
Reasons for cooking food
Texture of food improved
High temperatures kill harmful microbes
Taste of food improved
Enhanced flavour
Makes easier for body to digest
Video clip
4
How can we cook food?

• Think quietly of three ways to cook food.
• Share with your neighbour come up with four
  ways.
• Now lets see how many we have as a class

• microwave
• conventional oven
• boiling
• steaming
• grilling
• frying.

5
Comparing the different ways
6
Is cooking chemistry?

• Cooking involves chemical reactions.
• ENERGY is usually put IN.
• The appearance of the food changes.
• You cannot go back the other way!

7
Structure of proteins
Primary - molecules
8
Secondary molecules coil up
9
Tertiary a 3D structure
10
Quaternary
11
Keywords

• gnoocki
• neptroi
• ynereg
• leucomle
• txeutre
• clamehci
• lberireervis
• nimalub idgste
• dereatned

12
Chemistry and Baking

• MUST know why cakes and bread rise
• SHOULD understand a baking word equation
• COULD complete a symbol equation

13
Tatties!

• When a potato is cooked, its (lecl) walls break
  down and (hcrats) grains burst. This makes it
  softer and easier to (tsegid).

14
Investigating thermal decomposition
3 spatulas of sodium hydrogen-carbonate
One quarter full with limewater
Put your thumb over it and shake it to test for
carbon dioxide

• Can do tasks
• Test for CO2
• Heat something safely

Heat strongly
15
Baking powder

• The most important chemical in baking powder is
  sodium hydrogencarbonate
• NaHCO3
• When heated during cooking, this breaks down
• Thermal decomposition

16
The chemical reaction
heat
Carbon dioxide
Sodium hydrogencarbonate
Sodium carbonate
Water
heat
NaHCO3
Na2CO3
H2O
CO2
NaHCOOO
NaNaCOOO
HHO
COO
17
Summary

• How else might cooks get a gas into food?
• Think about what you add to bread to make it
  rise.
• How about meringue and whipped cream?
• How about coke?

18
Can you now

• Name the most important chemical in baking
  powder?
• Write a word equation showing the thermal
  decomposition of sodium hydrogencarbonate?
• Write a balanced symbol equation showing the same
  reaction?