1.2 Water – Temperature and Dispersions
Objectives
- Relate descriptive temperature terms to the observable changes in water at various temperatures.
- Demonstrate correct operation of various range-top cooking utensils using water as a medium of heat transfer.
- Differentiate among true solutions, colloidal dispersions, and suspensions according to their various behavior characteristics determined by the size of the dispersed particles.
Laboratory Problems
- Observe water appearance at temperatures used in food preparation.
- Change state of dispersion by common food preparation techniques.
- Determine effect of dispersed phase on boiling point of dispersion.
Observe commonly used water temperatures in an open saucepan:
- Calibrate the thermometer with boiling water.
- Heat a saucepan of tap water; observe the water at the following temperatures:
Temperature Conversion:
°C = (°F − 32) ÷ 1.8
°F = (°C × 1.8) + 32
Lukewarm temperature (30–37ºC ; ºF)
Does lukewarm water feel warm or cool to the touch?
What is normal body temperature? ºC; ºF.
Simmering temperature (85–99ºC ; ºF)
Describe the surface appearance of simmering water:
Boiling temperature (100ºC ; ºF)
Describe the surface appearance of water at:
a slow boil ( = actual recorded temperature)
a rapid (rolling or fast) boil ( = actual recorded temperature)
- What are the advantages of cooking foods at a slow boil rather than at a fast boil?
- When might a fast boil be advantageous?
Determine maximum water temperatures of other range-top utensils:
Double boiler
Heat 3 cups of water in upper part of a double boiler over 3 cups boiling water in the lower part. (Water in the lower pan should not touch the upper pan.)
- Will the water in the upper part boil if boiling water in the lower part touches the top part of the double boiler?
- List appropriate uses for a double boiler:
Steamer
Put 3 cups water in the bottom part of a steamer, and a maximum temperature thermometer in a custard cup filled with water in the top part.
- How would the rate at which foods cook in a steamer compare to the rate in a saucepan? Explain.
- List appropriate uses for a steamer:
Pressure saucepan
Put 1 cup water in a pressure saucepan and place maximum thermometer in custard cup filled with water on rack. Following directions for the saucepan, hold at 10 lbs. pressure for 5 minutes.
- At what temperature does water boil under
-
- 5 lbs. pressure 109 ºC; ºF.
- 10 lbs. pressure ºC; 240 ºF.
- 15 lbs. pressure 121 ºC; ºF.
- Temperature decreases 1°C for each 960 foot increase in altitude.
At what temperature would water boil in Denver, Colorado (altitude approximately 5,000 feet above sea level) under 10 lb. pressure?
ºC; ºF.
- How would the rate at which foods cook in a pressure saucepan compare to the rate at which they cook in a regular saucepan? Explain.
- List appropriate uses for a pressure saucepan.
Measure effect of dispersed phase on boiling point using sugar, salt, gelatin, or bran:
- Pour 2 cups of water into a saucepan. Throughout the exercise, add boiling water as needed to maintain this level.
- Bring water to a boil. Record boiling temperature in the table; then add 2 tbsp. assigned ingredient (sugar, salt, hydrated gelatin*, or bran) and stir.
- *Hydrate gelatin by sprinkling 3 tbsp. dry gelatin over ¾ cup cold water. Use 2 tbsp. of the hydrated gelatin for each addition.
- Bring water to a boil again and measure the boiling point. (Record results on the basis of a 100°C boiling point of water.)
- Repeat steps 2 and 3 until four additions of 2 tbsp. each have been made.
| Number of additions | Sugar
state of dispersion |
Salt
state of dispersion |
Gelatin
state of dispersion |
Bran
state of dispersion |
| 0 | ||||
| 1 | ||||
| 2 | ||||
| 3 | ||||
| 4 |
