What Causes Ice Crystals on Frozen Food?

Why Ice Crystals Form

• The most common reason large ice crystals form in your frozen food is slow, uneven freezing. Ice crystals do not form during more rapid freezing because the food molecules cannot form a six-sided snowflake before the freeze is complete. Slower freezing results in larger, less-manageable ice crystals that cause damage to the food. In the case of fresh fruits and vegetables, ice crystals can form because you have not dried the produce completely. This extra water on the surfaces of the fruits and vegetables eventually leads to a mushier product.

Preventing Ice Crystal Formation

• You don't want to go to all of the trouble of freezing food just to end up with a mushy mess. Prevent large ice crystals from forming by taking the following steps: Encourage food to freeze rapidly. If your freezer has a quick freeze shelf, use it for items you wish to freeze. Never stack items you wish to freeze, instead distribute them throughout your freezer to allow for more uniform freezing. When the items have frozen solid, you can move them around and stack them as you wish. Dry fresh foods thoroughly before freezing. If you are freezing strawberries or green beans from your garden, it is important to be sure they are completely dry to avoid ice crystal formation. Keep your freezer at or below a temperature of 0 degrees Fahrenheit if possible, as lower temperatures keep frozen foods more stable.

Other Factors That Affect Quality

• You may have eliminated almost all the ice crystals from your frozen foods, but that does not mean their quality will be the best. To ensure that freezing affects your foods' quality as little as possible, blanch vegetables. A quick dip in boiling water can help fresh veggies stay at their peak for longer, as boiling inactivates enzymes that encourage decay in the vegetables. Eliminate air if possible by using a vacuum sealer or carefully 'burping' plastic storage containers. Do not thaw and re-freeze, as this can cause a dip in quality and even food safety by allowing bacteria to reproduce.

Ice Crystal Safety Tip

• Occasionally, you may have a freezer unexpectedly malfunction while you are traveling, or your freezer may thaw while you are away due to a power outage. This can be dangerous because if the freezer starts working again or power is restored, it can be difficult to determine the thaw has occurred. Telltale ice crystals may be your only indication, but it's unlikely you have memorized the ice crystals in your frozen foods. To avoid this conundrum, place a zip-sealed bag of ice cubes in your freezer before leaving town. If a thaw occurs, the ice cubes will melt and refreeze as a solid block, showing you that you need to conduct a freezer purge.