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By Laura Stec

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About this blog: I've been attracted to food for good and bad reasons for many years. From eating disorder to east coast culinary school, food has been my passion, profession & nemesis. I've been a sugar addict, a 17-year vegetarian, a food and en...  (More)

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The Creamier, The Better

Uploaded: Nov 5, 2013
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)
tsp vanilla extract
2 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.

Comments

Posted by Donya, a resident of Barron Park,
on Nov 6, 2013 at 3:52 pm

Donya is a registered user.

This is such a nice and simple recipe. Too bad I have no cream at the moment. I will try it asap.

One minor suggestion: If you could give the weight of the salt ingredient it will make it easier. Thanks.


Posted by Laura Stec, a Palo Alto Online blogger,
on Nov 6, 2013 at 4:32 pm

Laura Stec is a registered user.

Thanks Donya - so simple but it amazed me! It's the little things I guess, right? Salt weighs 200g


Posted by Jay Park, a resident of Jackson Park,
on Nov 6, 2013 at 4:33 pm

@Donya:

There are two tablespoons per 1/8 cup. Just measure out 3/4 cup of salt, then add 1.5 tablespoons.

The salt isn't part of the ice cream mixture, it's just used in the manufacturing process, adding a bit more shouldn't affect the outcome.

Based on my own experience in making ice cream (with salt chilled ice), personally I would measure out 3/4 cup of salt, toss in a couple of tablespoons and not worry about it.


Posted by Elaine, a resident of another community,
on Nov 6, 2013 at 5:49 pm

This sounds like a great recipe, perfect for a party! I do hope everyone rinses and reuses the ziploc bags and substitutes a ceramic cup for the plastic cup. We don't have a lot of room in our landfill...


Posted by Donya, a resident of Barron Park,
on Nov 7, 2013 at 6:55 am

Donya is a registered user.

@Laura , @Jay

Thanks so much. I see that the amount of salt doesn\'t matter much.
Once at a Stanford Community day someone made ice cream using dry ice. It was delicious and practically instant. But I am nervous about dealing with with dry ice.


Posted by Laura Stec, a Palo Alto Online blogger,
on Nov 7, 2013 at 7:21 am

Laura Stec is a registered user.

Yes - the amount of salt in this recipe doesn't matter. The ice cream is soft - but the phase transformation is amazing, at least to me! And thanks Elaine for the good reminders! :)


Posted by Judee Humburg, a resident of Menlo Park,
on Nov 8, 2013 at 10:36 am

This sounds like so much fun and a great food adventure for students. At some point in the spring, maybe we'll try this with the Gunn classes that visit Common Ground Garden. I'm definitely saving this one! Reminds me of making butter with my Montessori classes many decades ago...a great way to get them moving on rainy days and disperse the kinetic energy into something delicious and useful for snacks! Thanks, Laura.


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