Freezing preserves food—and damages it. As the food freezes, ice crystals form that can rupture the food’s cell walls, allowing moisture (and nutrients) to leach out when the food thaws. But the faster the food freezes, the smaller the ice crystals are and the less damage that occurs. That’s why commercial food processors blast items such as peas, berries, and shrimp individually with extremely cold air before packaging them together—an approach known as IQF (individual quick-freezing). Without the surrounding items that block cold air and prevent items in the middle from fully freezing until the outer items have done so, the food can cool down more quickly.
Preserve Freshness by Freezing Food Fast
To prove the point, we weighed out three 12-ounce batches of raspberries and froze them three different ways. We froze the first batch as fast as we could by pouring negative‑320-degree liquid nitrogen over the berries in a baking pan. We approximated an IQF approach with the second batch by spreading the berries over a baking sheet to freeze. We froze the third batch packed into a zipper-lock bag. We recorded how long it took each batch to freeze and then thawed the berries and measured the amount of liquid each batch released.
Not surprisingly, the berries flash-frozen by liquid nitrogen suffered almost no loss of juice when thawed. But we weren’t prepared for the huge difference between the baking‑sheet berries and the ones frozen in the plastic bag. The latter took more than four times as long to freeze as the berries on the baking sheet and lost more than double the amount of liquid upon thawing.
Takeaway: To minimize damage to meat, vegetables, and fruits, it pays to first freeze the food in a single layer.
Time to freeze: <1 minute
Weight loss of thawed fruit: 4 percent
Time to freeze: 2 hours
Weight loss of thawed fruit: 12 percent
Time to freeze: 9 hours
Weight loss of thawed fruit: 30 percent