Chill drinks faster

This activity is part of our Science Lab series. Check out the ANU Science Lab for more experiments! In this activity, you will conduct a hands-on physics and chemistry experiment to test the fastest way to chill a drink using ice, salt, and thermal energy principles. Watch the video above to see how it's done.

How to chill a drink faster: materials & ingredients

For each test setup:

• 2 clear plastic bottles or cups (to hold your sample liquids)
• Water (to fill the test bottles)
• 4 sachets (or tablespoons) of white sugar
• A large container filled with ice
• 1/2 cup of table salt (sodium chloride)
• Infrared thermometer (or digital thermometer)
• Timer or stopwatch
• Spoon or stirrer

Safety Note: When using an infrared thermometer gun, take care never to point the laser beam directly at anyone's eyes!

How to chill a drink faster: step-by-step instructions

Method 1: chilling drinks in standard ice

1. Prepare your sample liquids: Fill two bottles with equal amounts of room-temperature water. Add 4 sachets of sugar to one bottle and shake until dissolved. Leave the second bottle as plain water.
2. Record starting temperatures: Use your thermometer gun to measure and note the initial temperature of both liquids (around 20.5°C).
3. Submerge in ice: Bury both bottles inside your ice bucket, making sure the ice covers as much of the bottle surface as possible.
4. Time the cooling: Set a timer for 10 minutes. When the time expires, pull both bottles out and immediately record their final temperatures.

Method 2: chilling drinks in an ice and salt bath

1. Reset the ice container: Drain any melted water, add fresh ice to your container, and thoroughly mix in 1/2 cup of table salt.
2. Prepare fresh liquids: Refill your two test bottles with room-temperature water and dissolve 4 sachets of sugar in one of them. Measure and record their starting temperatures.
3. Submerge in the salt-ice: Nestled both bottles deep into the salt and ice mixture.
4. Time the cooling: Set a timer for 10 minutes. Remove the bottles when the timer goes off and measure the temperature of each liquid again to compare results.

How does chilling drinks with salt and ice work? The science explained

Adding salt to an ice bath lowers the temperature of the ice much faster than standard ice alone due to a principle called freezing point depression.

Pure water freezes (and ice melts) at 0°C. When you add table salt (sodium chloride) to the ice, the salt ions dissolve into the thin layer of surface water and disrupt the water molecules from locking into a solid ice lattice:

• Adding salt lowers the freezing point of water from 0°C down to anywhere between -1°C and -20°C, depending on how much salt you add.
• Because the ice is forced to melt at a much lower temperature, it absorbs heat energy from its surroundings, including the drink bottle or cup sitting inside the bucket.
• This drastic drop in temperature creates a steeper heat transfer gradient, pulling thermal energy out of the liquid inside the bottle far faster than plain ice can.

Furthermore, sugary liquids cool and freeze differently than plain water because dissolved sugar molecules also lower the freezing point of the liquid inside the bottle.

Science fair projects & taking it further: experimenting with variables

Once you have mastered the basic salt and ice bath, try tweaking these variables to see if you can chill your drinks even faster:

• Agitation and rotation: Try continuously spinning or shaking the bottle inside the salt-ice bath during the 10 minutes. How does forced convection affect heat transfer speed?
• Varying salt concentrations: Test different amounts of salt (1/4 cup vs. 1/2 cup vs. 1 cup) to map out how salt concentration impacts the final temperature.
• Different beverage types: Compare plain water against commercial sodas, fruit juices, or milk to see how different sugar contents and ingredients react to the rapid cooling process.
• Different container types: Does a can cool faster than a plastic bottle? Does an open cup cool faster than a bottle with a lid?

Enjoyed this experiment? Explore more hands-on activities on the Science Lab ANU YouTube channel.