What it actually is
Freezing turns the water inside the product into ice, and ice occupies more space than the water it came from. Crystals push against cell walls and protein structures and rupture them. On thawing the water is free, and the damaged structure can no longer hold it, so it runs out.
Why it matters
It is weight lost, and it is visible: liquid in the bottom of a pack reads as a product that has gone wrong even when it is entirely safe. For a case ready product it is the single most common reason for rejection at the shelf.
What changes it
The rate of freezing, which decides crystal size; the number of freeze and thaw cycles the product actually goes through; and the water holding capacity the product had before it was ever frozen. A product that held water poorly fresh will drip badly thawed.
