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This week’s Science and Cooking class had an amazing project I have never seen before ? making ice cream in standard zip lock bags. Try it tonight with your kids or just be a kid yourself ? so much fun!
The physicist finally showed his face in class (I love physicists). “Ice cream,” he said, “is a product of phase transition” (foods that move from one physical state to another). In this case, the transition is water into ice.
One of the biggest challenges in making ice cream at home is getting it dense, smooth, and free of iciness. What’s interesting is that all things being equal, ice cream that we perceive as icy doesn’t contain more ice crystals, just larger ones. The crystals in smooth ice cream are so small that our tongue doesn’t detect them. So the goal is to try and keep the ice crystals small.
Want to prevent “icy” ice cream?
1. Control the water in the ingredients. (ex: fruit has more water than chocolate)
2. Add more sweetener. Sweeteners lower the freezing point of water, preventing some from turning to ice.
3: Freeze ice cream quickly (spread out in a pre-frozen pan to freeze).
ICE CREAM USING THE ALTERED PHASE TRANSITION OF WATER
For best results, use a scale to measure ingredients.
Materials:
2 large Ziploc bags, or other plastic bag of ~ 1gallon. Must seal completely.
2 small Ziploc bags Must seal completely
1 scale (optional)
1 oven mitt or towel
1 plastic cup
Ingredients:
90g heavy cream (about 6 tablespoons)
100g whole milk** (about 7 tablespoons)
20g sugar (about 1 tablespoon + one teaspoon)
¼ tsp vanilla extract
2 ½ cups ice
13.5 tablespoons salt
**Try other milks – soy, almond, rice, etc for a non-dairy version. Replace one-to-one.
1. Fill a large ziploc bag with the ice (about 1/3 full). Add the salt to the ice.
2. In a separate small zip-lock bag, add heavy cream, milk, sugar, and vanilla extract Seal WELL, trying to press out air to maximize contact with the ice.
3. Place the small bag with the ice cream ingredients inside the large bag with ice. Place the entire package into a second large bag to prevent leaking.
4. Massage, or gently toss the bag around until the ice cream becomes solid. If possible, try to do this on a cold surface so the ice doesn’t melt. You should use oven mitts or hand towels to handle this part, so your hands don’t get cold, thus letting you massage the ice cream better. Constant mixing is key to getting a good texture!
5. Remove the small bag with ice cream from the large bag with ice. Wipe off the top of the small bag and then open it carefully. If it seems solid and delicious, you’re done! If not, before the ice melts, add more ice and salt and repeat step 4 until it’s ready.
If you do try this experiment at home, please add a comment to report your results.
