How to Make an Instant Slushy (and How It Works)


Instant Slushy
All you need for making an instant slushy is a drink, ice, and salt.

Making an instant slushy at home is an exciting project that combines science with a delicious reward at the end. Here are two methods of making your own instant slushies. The first uses juice or a soft drink with zipper plastic bags, ice, and salt. The second method uses a sealed bottle or can, a large bowl of ice, and salt. We’ll also dive into the science behind these methods and explore if it’s possible to create slushies using alcoholic beverages.

Instant Slushy Method 1: Zipper Plastic Bags

The first method for making in instant slushy uses two plastic bags. The smaller bag contains juice or a soft drink, while the larger bag contains salt and ice. Kosher salt is the best salt for this project because of its larger grain size, but any salt works.

Materials:

  • Gallon-size zipper plastic bag
  • Quart-size zipper plastic bag
  • Ice cubes
  • Salt
  • Juice or soft drink
  • Towel (for insulating your hands and for clean-up)

Instructions:

  1. Fill the Gallon Bag with Ice and Salt: Fill about half of the gallon-size zipper bag with ice cubes. Add 1/2 cup of table salt over the ice. Don’t worry about the exact quantities. Basically, you need ice, some salt, and enough leftover space for the smaller bag.
  2. Prepare the Drink: Pour juice or a soft drink into the quart-size zipper bag until it’s about halfway full. Seal the bag tightly, ensuring there is no air inside.
  3. Combine the Bags: Place the quart-size bag containing the juice or soft drink into the gallon-size bag containing the ice and salt. Seal the gallon-size bag.
  4. Shake and Mix: Shake the bags vigorously for about 5-7 minutes. Make sure the ice surrounds the quart-size bag on all sides.
  5. Check for Slushiness: After shaking, carefully open the gallon-size bag and take out the quart-size bag. The liquid should now be a slushy consistency. If it is not, seal the bag and place it back inside the larger bag of ice for a bit longer.
  6. Enjoy: Open the quart-size bag carefully and enjoy your homemade slushy using a spoon or straw.

Instant Slushy Method 2: Sealed Bottle or Can

While the plastic bag method is quick, it’s also a bit messy. Fortunately, you don’t need to open your drink before turning it into a slushy.

Materials:

  • Sealed plastic bottle or can of soft drink or soda
  • Large bowl
  • Ice cubes
  • Salt

Instructions:

  1. Chill the Drink: You don’t have to chill the drink first, but it’s quicker if you start with a cold container. Place the unopened plastic bottle or can in the freezer for about 1-2 hours, but not long enough for it to freeze solid. Alternatively, refrigerate it several hours or overnight.
  2. Prepare the Ice Bowl: Fill a large bowl with ice cubes and sprinkle generously with salt.
  3. Place the Drink in the Bowl: Nestle the chilled bottle or can into the salted ice. Make sure it’s surrounded on all sides.
  4. Wait and Observe: Let it sit for 15-30 minutes. Occasionally swirling the bottle or can speeds the process, but isn’t necessary. Note: Diet drinks turn into slush much more quickly than sugary ones!
  5. Check for Slushiness: Carefully open the bottle or can. The liquid now has a slushy consistency.
  6. Enjoy: Pour the contents into a glass and enjoy your instant slushy!

The Science Behind It: Freezing Point Depression and Supercooling

Two of the scientific principles at work in the instant slushy project are freezing point depression and supercooling:

Freezing Point Depression

The addition of salt to ice lowers the freezing point of water through a phenomenon known as “freezing point depression.” Normally, water freezes at 0°C (32°F), but when you add salt the freezing point drops as low as -21 °C or -5 °F. The way this works is that a bit of ice melts and dissolves salt into its ions (Na+ and Cl) in water. Dissolving salt and melting ice absorb heat from the surroundings, making it cold. But, the ions get between water molecules and disrupt their crystallization back into ice (which would release heat). The result is an environment even colder than the average home freezer.

Supercooling

In the sealed bottle or can method, the liquid cools below its normal freezing point without turning into a solid. This is a state known as “supercooling.” When you disturb a supercooled liquid, it rapidly freezes into a slushy consistency.

Alcoholic Slushies: Is It Possible?

Yes, you can make a slushy using an alcoholic beverage, but there’s a catch: the alcohol content needs to be low or else you need a different salt. The freezing point of alcohol is much lower than that of water, which means the higher the alcohol content, the lower the freezing point. Generally, beverages with an alcohol content of around 5% or lower can be turned into slushies using these methods. In other words, “coolers” work well, but wine probably won’t. For higher alcohol content, you need a lower temperature. Swapping road salt (CaCl2) for regular salt (NaCl) gives you a temperature around -20 °F.

In summary, making an instant slushy is not just a fun activity but also a fascinating science experiment. It’s a great way of exploring the properties of matter and the impact of temperature and solutes on the freezing point. For more science fun, make ice cream in a baggie using the same principles.

References

  • Atkins, Peter (2006). Atkins’ Physical Chemistry. Oxford University Press. ISBN 0198700725.
  • Debenedetti, P. G.; Stanley, H. E. (2003). “Supercooled and Glassy Water”. Physics Today. 56 (6): 40–46. doi:10.1063/1.1595053
  • Pedersen, U.R.; et al. (August 2016). “Thermodynamics of freezing and melting”. Nature Communications. 7 (1): 12386. doi:10.1038/ncomms12386
  • Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey (2002). General Chemistry (8th ed.). Prentice-Hall. ISBN 0-13-014329-4.