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# How Does Milk Freeze into Ice Cream?

##### Approximate Time Required to Complete the Project

2 hours.

Learn how milk freezes into ice cream.Does the fat content of the milk affect how quickly it freezes into ice cream?What is the role of salt in the freezing process?Watch how matter turns from solid to liquid (the melting ice) and from liquid to solid (the freezing milk).

• Milk: 1 cups each of chocolate milk, whole milk; non-fat milk
• Vanilla flavoring (1 teaspoons)
• Sugar (4 tablespoons)
• 2 medium-sized bowls
• 2 ice "scoops" (use sturdy 8 oz. plastic cups)
• Salt: 1 26 oz. canisters of iodized table salt (you’ll need at least 18 oz.)
• Measuring Cups and spoons
• Scissors - 3-4 pairs
• Ice – 3 pound bag, or about 12 cups
• Resealable plasticbags - 6 sandwich size and 6 gallon size, plus extras
• Mittens: 1 pair
• 6 oz. Or larger Cups for Ice Cream - 6
• Spoons - 6
• Timer or clock
• Pencil and paper

What could be more fun than making ice cream in a bag?Eating it, of course.Well, in this experiment you’ll get to do both!While you’re making your ice cream, you’ll time how long it takes for the milk to freeze and the ice to melt.

• Does it take longer for non-fat milk or whole milk to freeze?Why?
• Is there a difference between chocolate milk and vanilla milk?

In this science project, you will make ice cream.You will use milk with differing percentages of milk fat and time how long it takes for the milk to turn solid.You will learn about two of the three states of matter: liquid and solid. You will freeze the liquid milk into solid ice cream by using ice and salt. While the melting point of the ice stays at 32 degrees F, the salt lowers the freezing point of water to below 32 degrees.That’s helpful, because milk’s freezing point is lower than that of water, about 31 degrees F.It needs a colder temperature than water does in order to freeze.

• Milk fat: Milk fat, or the fat content of milk, is the proportion of milk made up by butterfat.In this experiment you will use non-fat milk, which has 0% fat, and whole milk, which has approximately 4% fat.The chocolate milk you use might be 2% fat, although this might vary based on the brand you choose.
• States of Matter: States of matter are the forms that different phases of matter take on.The states are solid, liquid and gas.In a solid state, the matter maintains a fixed volume and shape.An example of something solid is an ice cube.Water freezes into ice at 32 degrees F.A liquid maintains a fixed volume but adopts the shape of its container.An example of a liquid is water.A gas expands to occupy whatever volume is available.Liquid water turns into steam, a gas, when it is heated to the boiling point, 212 degrees F. (Some people also talk about a fourth state, plasma, which is a type of gas which conducts electricity, but that’s a bit complicated for our experiment).
• Melting Point: The melting point is the temperature at which a given solid turns into a liquid.At a temperature higher than the melting point, the matter stays liquid.For ice, the melting point it 32 degrees F.
• Freezing Point: The freezing point is the temperature at which a given liquid turns solid.To make ice cream, we use salt to lower the freezing point of water so that it is below 30 degrees F.
1. Start by making a hypothesis.Do you think the whole milk or the nonfat milk will take longer to freeze?Why?
2. Make a chart, so that you’re ready to record your findings.There’s an example below.You will have enough ingredients to do this experiment twice.
3. Use the vanilla and sugar to flavor the whole and non-fat plain milk.These flavorings will turn your “plain cream” ice cream into vanilla ice cream.
• Pour the whole milk into one of your medium sized bowls.
• Pour the non-fat milk into the other bowl.
• To each bowl, add 2 tablespoons of sugar and 1/2 teaspoon of vanilla.
• Stir well.
4. Pour one cup of whole, vanilla milk into one of the small plasticbags.Seal the bag well.Try to press out any extra air.

1. Fill the other two small bags.Pour one cup of chocolate milk in one bag, one cup of non-fat vanilla milk in the other.Make sure both bags are well sealed.Put these in the refrigerator.
2. Fill a large, gallon-sized freezer bag half full with ice. Add 3 ounces (6 tablespoons) of salt.
3. Put the smaller bag of whole, vanilla milk into the larger bag and seal.Try to make sure the ice in the bigger bag surrounds the smaller bag.

1. Note what time it is, or set your timer.
2. Put on the mittens.
3. Shake and knead the bag gently until the ice cream thickens.This may take about 10 minutes.
4. Record what time it is when the ice cream thickened.Put the ice cream in the freezer while you continue working.
5. Repeat steps 6 through 11 with the two other types of milk, the chocolate and the non-fat, vanilla milk.
Chart: Ice Cream
 Whole Milk Non-Fat Milk Chocolate Milk Time to Freeze (in minutes)
1. General Chemistry Online: FAX: Solutions: Why does salt melt ice?
2. Science on the Brain
3. Salted Ice and Temperature Drop: Ask a Scientist, Argonne National Lab
4. Hurley, Walter L.Milk Composition – Freezing Point: University of Illinois

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