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SPU 27 2012 Final Review 2

SPU 27 2012 Final Review 2. Heat Transfer. Equations of the Week. Heat Transfer. Again, how does heat move into food? What are critical temperatures? How can you use sous vide to manipulate cooking temperatures?. Sample Problem.

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SPU 27 2012 Final Review 2

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  1. SPU 27 2012 Final Review 2

  2. Heat Transfer

  3. Equations of the Week

  4. Heat Transfer • Again, how does heat move into food? • What are critical temperatures? • How can you use sous vide to manipulate cooking temperatures?

  5. Sample Problem • Say you want a hard-boiled egg with a solid yolk; the transition temperature for the yolk to be well-coagulated is about 70C. How long does it take for the heat to reach the center of an egg with a radius of 2cm after the egg is immersed in boiling water? Use the equation of the week.

  6. Maillard & Caramelization Reactions • Why are these reactions important? • What food components are involved in each? • What temperature do they happen at? • How could you increase the rate of these reactions?

  7. Sample Problem • Even in a hot oven, most foods do not go over 100C. Why not? What would you expect the temperature curve to look like once the equation of the week says the temperature should be above 100C?

  8. Viscosity and Polymers

  9. What is viscosity? • Force of fluids that resists flow • What determines this? • The time it takes for molecules to move around their neighbors. • What does a longer time mean? Shorter? • Equation of the week  • Elasticity x relation time • Units?

  10. How do we measure viscosity? • Think milkshake lab • What things did we need to measure and why? d

  11. Measuring Viscosity Cont. • Distance ball dropped & time it took ball to drop can be used to calculate terminal velocity • What is terminal velocity? • Drag = Gravitational • In other words, • Drag – gravitational = 0 • No net force!! VT = d/t Drag force Gravitational force

  12. What do the forces depend on? • Gravitational force: • How buoyant the object is • In other words  • Drag force • Depends on viscous flow

  13. Putting them together… • Again think of what it means to be at terminal velocity… no net force! • So you can set drag and gravitational forces equal to each other FDrag FGravity

  14. Concept question • What happens to a feather and bowling ball falling in a vacuum?

  15. What are common values? • Pay attention to units!

  16. What are some ways to increase viscosity? • Starch example: Higher temperature

  17. What are some ways to increase viscosity? • Protein example: Thickening Curdling

  18. Polymers • Polymers = long chains of monomers • Examples? • Proteins (monomers = amino acids) • Complex carbs (monomers = simple sugars such as glucose)

  19. Polymers Cont. • How do you calculate the effective size of a polymer? • Size = sqrt (# monomers*size monomer) • Size monomer can be estimated by its area • What does calculating the size of a polymer take into account that just calculating its length does not?

  20. Emulsions & Foams

  21. Emulsions • Mixture of droplets of one liquid dispersed within another liquid Oil-in-water Direct emulsion Water-in-oil Indirect emulsion

  22. Concept Question • What are some problems with making emulsions such as mayonnaise or aioli? • How can emulsions “fail”? • How do chefs use other ingredients to manipulate the chance of failure?

  23. Surfactants! hydrophobic likes oil hydrophilic likes water Stabilize by lowering surface energy

  24. Surfactants cont. • Surfactants = Ampiphilicmolecules

  25. Emulsion Failure

  26. Volume fraction What does it mean conceptually to have a higher volume fraction? What is the critical volume fraction?

  27. Equation of the week Emulsions are elastic above the critical volume fraction

  28. Equation of the week • What’s the critical volume fraction? • How would you increase the elasticity? • How would you decrease it?

  29. Foams How do foams fail? How do you stabilize them?

  30. Chemistry 1

  31. Recipes • Include instructions and ingredients • Ingredients come in different ratios What constrains sets of recipes?

  32. Chemical Reactions & Food • What reactions have we seen already? • Digestion • Phase transition (more a physical reaction) • On that note, what’s the difference between physical * chemical reactions? • Spherification • Etc.

  33. Four Ways of Leavening • Air, steam, yeast and chemical • Chemical • Baking soda and baking powder • What’s the difference?

  34. Baking Soda • Basic reaction • Base + acid  gas • Baking soda + vinegar  gas • Sodium bicarbonate + acetic acid  sodium acetate + water + carbon dioxide Equation must be balanced! What does this mean?

  35. Practice Problem: Baking Soda • How much gas (volume) will 1 tsp of baking soda produce? • Assume for simplicity, 1 tsp ~ 5g • Molecular weight of baking soda = 84g/mol

  36. Practice Problem: Baking Soda • First calculate # moles of baking soda • [0.06 moles] • Since 1: 1 ratio  0.06 moles of CO2 produced • Calculate corresponding volume • 1 mole of any gas at STP = 22.4L • So 0.06 * 22.4 = 1.3 L • Will a loaf of bread with this amount of baking soda actually rise this much?

  37. Baking Powder • Baking powder is baking soda + cream of tartar

  38. Browning • Carmelization • Maillard • Fruit • What’s interacting in each of these? • What are some ways to increase browning reactions?

  39. Browning • Carmelization • Happens at 150C between sugars • Maillard • Happens at 120C between amino acids and carbs • Can increase this & carmelization by adding baking soda • Fruit • Enzymes cause the oxidation of phenolic compounds • Can increase by reaching the optimal temperature or adding salt and decrease by lowering temperature, lowering pH or raising it until the enzymes denature

  40. Chemistry 2

  41. Microbial Growth • Happens exponentially

  42. Practice problem • Let’s say there is one E. coli bacteria in your spinach salad. It has a generation time of 0.35 hours. How long would it take to be unsafe to eat according to the USDA (100,000)?

  43. Practice problem 2 • If your eggs started out with 1 million Salmonella microbes, how long would you need to pasteurize them to reduce them to a USDA safe amount (reduction to 10^-6.5)? • .5 hours = division time

  44. Life of microbes

  45. What does bacterial growth depend on? • Environment • pH • Temperature • Food

  46. Examples of Good Microbes • Yeast • Digestive microbes • Uses • Preservation • Flavor intensification • Intoxication

  47. Fermentation • Can preserve vegetables • Olives, kimchi, sauerkraut • Brewer’s yeast • Converts sugar to alcohol (form of self defense actually) Glucose  carbon dioxide + ethanol C6H12O6 2CO2 + 2CH3CH2OH

  48. Fermentation Cont • Pay attention to how the molar coefficients on this example are different (12) than in a baking soda reaction where it’s a 1:1 ratio Glucose  carbon dioxide + ethanol C6H12O6 2CO2 + 2CH3CH2OH The molar coefficients are there to balance the number of C’s, H’s and O’s (as well as any other atoms) in the reactants and the products.

  49. Practice Problem: Fermentation • How much alcohol would a starting grape juice with 500g of sugar produce? • MW sugar = 180g • MW alcohol = 46g • If you had 1000g of wine as a final product, what would the alcohol content be? • Is this realistic?

  50. Fermentation Cont. • Also seen in milk • Yogurt, sour cream, buttermilk

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