UPD8

Turkey

Learning objectives

Students will learn:
• About some of the chemical reactions that happen when meat cooks
• About heat transfer in cooking, including the factors that affect how quickly heat is transferred to the centre of the meat

Try the activity

• turkey_teachers_notes
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You will need Acrobat Reader installed to open the activity sheets.

Curriculum link

11 – 14 Heating and cooling (KS3 QCA module 8I)
• The mechanisms of heat transfer: conduction, convection and radiation, and applying them to familiar contexts

14 – 16 How science works: communication skills
• 3c: present information and develop an argument using scientific, technical and mathematical language, conventions and symbols and ICT tools.

14 – 16 Energy, electricity and radiations
and Chemical and material behaviour

See downloadable teachers notes for details of individual specifications

Running the activity

Display page 1, which states the problem and sets the challenge. Tell students that the recommended cooking time for a 5 kg turkey is 4 hours at about 170 �C.

Display page 2, which describes some of the chemical changes that occur as a turkey cooks. Draw attention to the TV chef's final speech bubble, which gives specific cooking advice. Point out some of the difficulties – some turkey parts are best cooked slow and cool; others fast and hot... [In expensive restaurants, chefs cook all the parts separately. They show another turkey to the diners, take it away 'to be carved' and return with meat carved from the separately cooked parts].

Page 3 is about cooking times. It's a tough turkey, best suited to your more mathematically inclined students. Either display this page, or give copies to small groups of appropriate students. Tell them to follow the instructions to calculate the cooking time for the 10 kg turkey. You might like to give students small cubes – or lego – to help them visualise the problem (although you need a lot of cubes – 125 per group!)

Now give small groups a copy of page 4. Ask them to use it to plan their TV chef presentation to Sam's dad. If students have not done the task on page 3, they will not be able to complete the cooking time box. Then get students to give their talks – have fun!

Notes:
Peter Barham is the scientist who advises Heston Blumenthal. In his book 'The Science of Cooking' (Springer 2001), he suggests cooking a turkey like this:
• Heat the oven to 170 �C. Put the turkey in a roasting tin. Pour 200 ml of stock into the bottom of the tin. Spread butter over the turkey breasts. Cover the breasts with aluminium foil. Use a wooden skewer to fix the foil in place (not a metal one, as it conducts heat into the breast quickly and could lead to over-cooking)
• During cooking, check regularly to make sure the stock has not all boiled away – the purpose of the stock is to keep the turkey moist and limit the cooking temperature to 100 �C. The legs and wings will be heated by the steam from the stock and the connective tissue will be denatured slowly, making the meat tender. The foil-covered breast is insulated from the steam and protected from radiant heat.
• After 5 hours 45 minutes, drain off any remaining stock. Remove the foil from the breast. Allow the temperature to rise. The breast cooks quickly and Maillard reactions occur on the surface of the turkey. Remove from the oven after about 6.5 hours.


The calculation described on page 3 goes like this:
If I double the weight of the turkey:
The volume, a three-dimensional quantity, gets bigger by a factor of
23/3 = 2.00
The surface area, a two-dimensional quantity, gets bigger by a factor of
22/3 = 1.59
The distance to the center, a one-dimensional quantity, gets bigger by a factor of 21/3 = 1.26
In the case of the turkey, we doubled the weight—which turns the problem upside down. The square-cube law still applies, but in this manner: The distance to the center of the turkey, a linear dimension, increases as the cube root of the weight, and the area increases as the cube root squared.
Increase in cooking time If you put the three factors together, the cooking time increases by 2 X 1.26 = 1.59. (4 hrs. X 1.59 = 6.4 hrs.)
1.59

Web links

News links

Royal Society of Chemistry

Very clear information from the Royal Society of Chemistry, suitable for teacher use and 'A' level chemists:

Exploratorium

Browning the breast and Maillard reactions

Wikipedia

More on Maillard reactions

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