For those who have ever wondered why their homemade ice looks cloudy while bar ice is crystal clear, a food scientist has revealed the simple secret. The key lies not in the water, but in the freezing process itself.
The Science Behind Cloudy Ice
Professor Paulomi Burey, a food science expert at the University of Southern Queensland, explains that typical cloudy ice is filled with tiny trapped impurities. "Homemade ice is often cloudy because it has a myriad of tiny bubbles and other impurities," she wrote in an article for The Conversation.
When water freezes in a standard ice cube tray, the process happens from all sides inward. This action traps and pushes whatever is floating in the water—such as air bubbles, dissolved minerals, and gases—toward the centre of the cube. With nowhere else to go, these impurities create the characteristic cloudy core.
The Solution: Directional Freezing
The professional method for achieving bar-quality clarity is a technique called directional freezing. This process forces water to freeze in one single direction rather than from all sides simultaneously.
"In practice, this means insulating the sides of the ice container so that the water freezes in one direction, typically from the top down," Professor Burey said. The heat transfer happens faster through the exposed top, creating a controlled freeze that pushes all impurities to the opposite end.
How to Make Clear Ice at Home
You do not need special equipment or distilled water. Follow these straightforward steps:
- Take an insulated container, like a drinks flask, cooler box, or insulated mug.
- Fill it with tap water and place it, uncovered, in your freezer.
- Check it periodically. You will see a clear block forming with a small cloudy section concentrated at the bottom.
- Once the ice is mostly solid, tip it out. You can either scrape away the remaining unfrozen, cloudy water or let the block freeze completely.
- If fully frozen, use a large serrated knife to cut off the cloudy portion. The remaining clear ice can then be cut into perfect cubes or shapes for your drinks.
Professor Burey also noted that commercially available insulated ice cube trays can simplify this process further.
Why Clear Ice is Superior
Beyond its elegant appearance, clear ice offers practical benefits for your drinks. "Clear ice is denser and melts slower because it doesn't have those bubbles and impurities," Professor Burey added. This slower melt rate means your cocktail or soft drink dilutes less quickly. Furthermore, its solid structure makes it less prone to crumbling, allowing for easy cutting into sophisticated shapes.
Debunking Common Ice Myths
The food scientist was keen to dispel popular but ineffective tricks. Using boiling water, for instance, does reduce dissolved gases but does not remove all impurities and has no effect on the freezing direction, so cloudiness remains. A study in the International Journal of Refrigeration confirmed this, showing very similar clarity in cubes made from both tap and boiled water.
Similarly, using distilled or filtered water does not prevent cloudiness if frozen using conventional, multi-directional methods. The freezing process is the critical factor.
With the average ice cube taking three to four hours to freeze, there is ample time to experiment with this scientific method before your next gathering. As Professor Burey concluded, "With a little help from science you can make clear ice at home, and it's not even that tricky."
