# 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:

1. Calibrate the thermometer with boiling water.
2. 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)

1. What are the advantages of cooking foods at a slow boil rather than at a fast boil?

1. 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.)

Record the highest temperature reached:                         ºC;       190–198        ºF.
1. Will the water in the upper part boil if boiling water in the lower part touches the top part of the double boiler?

1. 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.

Record highest temperature reached:            91             ºC;                        ºF.
1. How would the rate at which foods cook in a steamer compare to the rate in a saucepan? Explain.

1. 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.

Record highest temperature reached at 10 lbs. pressure:                         ºC;          240              ºF.
1. 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.
1. 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.

1. 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.

1. List appropriate uses for a pressure saucepan.

### Measure effect of dispersed phase on boiling point using sugar, salt, gelatin, or bran:

1. Pour 2 cups of water into a saucepan. Throughout the exercise, add boiling water as needed to maintain this level.
2. 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.
1. *Hydrate gelatin by sprinkling 3 tbsp. dry gelatin over ¾ cup cold water.  Use 2 tbsp. of the hydrated gelatin for each addition.
3. Bring water to a boil again and measure the boiling point. (Record results on the basis of a 100°C boiling point of water.)
4. 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