The typical home freezer has two separate cooling zones that affect how long it will take for objects inside to freeze—the first zone is called primary or fast freeze, while the second is called secondary or slow freeze. When an ice tray is placed inside for freezing, it will be brought into either zone based on its location. For instance, items placed on the floor of the freezer will be in its fast freeze zone, while those placed on a shelf would go into secondary.
When cold air is forced out of the fast freeze zone by new cold air coming in, it creates an area where warm air is displaced—this area is called dead air space and causes items near it to take longer to freeze than items closer to solid surfaces (walls). Large cubes that take more time for liquid water to change into solid ice can also contribute to slower freezing times. Ice will typically freeze most quickly during periods when night falls with little wind chill.
- Freezers with bottom-mounted freezers (freezer shelves are at ground level) tend to keep items frozen than top-mounted freezers. This is because the cooling vent in top-mounted freezers is blocked by items on the freezer shelf, thus degrading their performance. Temperature also plays a role in how long it takes for ice to freeze. Ice will thaw faster at higher temperatures than lower ones.
- Materials used in tray construction can affect freezing times. Plastic trays are more efficient at retaining cold than metal or glass trays, which will create a longer freezing time since heat transfers quicker through these types of materials than plastic materials. The addition of water additives such as salt can increase cooking times since they act as an anti-freeze and melt ice faster by changing its freezing point (this is why salt is sometimes sprinkled on sidewalks that occasionally get snowed upon). Finally, ice in trays located in freezers that are opened frequently (i.e. habitually) will take longer to freeze because the warm air entering each time warms up the water in the tray—the addition of cold air does not completely compensate for this heat loss, causing all contents to take much longer until they fully freeze.
- Ice production rates can vary significantly depending on household size, but it typically takes 3 to 4 hours for ice cubes to form and be ready to use in drinks or food recipes. According to Home Economist Gina Boehlje at Purdue University, this rate varies greatly depending upon freezer temperature, cube size, water quality and depth, amount of insulation present inside freezer walls, household habits involving opening/closing the freezer, and the temperature of the outside air to which your freezer is exposed.
- Ice cubes that are smaller will freeze faster than large ones since there is less water to freeze. If you have an ice maker feature on your refrigerator, chances are this results in thinner/smaller cubes—which again freezes faster since there is less water to freeze. Boehlje notes that crystal formation can also affect how quickly ice freezes, perhaps leading to longer freeze time periods if the crystals form around tiny particles or impurities present in water samples used for filling trays.
- Ice frozen in metal trays tend to take much longer because heat transfers more easily through these types of containers compared with plastic ones. Glass trays are even worse at retaining heat and thus lead to longer ice-freezing periods.