Why does large, clear ice cubes take so long to form?

Why does large, clear ice cubes take so long to form?

It takes how long to make 4 two-inch clear cubes!?!? If I had a dollar for every time I heard this, I would be purchasing top shelf spirits for my craft cocktails. They say all good things come in time, and that goes for large, clear craft ice too. Depending on the equipment and method used, large clear craft ice can take a few hours to days to make. This is quite different than the on-demand ice production we have become accustomed to in our refrigerators or at the favorite local fast food joint. Trust me though, there is science behind the required freeze time. Let’s dive in! 

The speed at which ice freezes is driven by thermal conduction which is the transfer of energy from one area to another. In the case of clear ice, ice is made by removing energy from water through a cold surface in one direction and insulating the other 5 sides to prevent energy loss. Over time, the removal of energy induces a phase transition from a liquid (water) to a solid (ice). This transition occurs at the water/ice boundary layer, which moves as the ice grows. 


The rate at which this ice layer progresses or grows is dependent on several factors and is summarized by Fourier's Law of Heat Conduction


In simpler terms....  



We can see from this relationship that as the height of ice increases, the growth rate of the ice slows or decreases.  Envision a thick insulator forming between the cold surface and the water/ice boundary layer over time. Thicker ice layers reduce energy transfer at the boundary layer which in turn reduces the growth rate and increases the time needed to make large, clear ice cubes. Speed of ice making can be changed by adjusting conductive surfaces and substances (think multiple cube sides exposed to freezing conditions and water versus air as the conductor).  


Improving growth rate through active cooling

The cooler method, complex silicone molds and northern lakes form ice in the top down directional freezing method. The top down freezing methods rely on cool air which is a poor conductor, leading to long freeze times (days). The Klaris Ice Maker has an actively cooled, aluminum plate that continuously draws energy from the bottom up, enabling clear craft ice in hours, not days.  This is 2-3X faster than the top down methods on the market today. 


Improving growth rate through increased cooling surfaces

Another way to increase ice growth rate is by providing greater cooling surface area. This is how simple silicone molds and conventional ice trays achieve faster ice production cycles, allowing energy to be removed from all 6 faces of cubes at once. This results in much faster freeze times (~3X) than directional freezing, but these cubes capture impurities and gases as the water freezes from the outside surfaces then inward, resulting in cloudy ice.  


If you are antsy for that craft cocktail experience, remember all large, clear craft ice comes in time, but much faster than conventional methods with Klaris! Cheers to clear ice! 

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