Most of a product's water crystallises as it freezes, and the zone where the most ice forms in muscle tissue is roughly -1 to -5 °C. Cross it quickly and small, even crystals form with little damage to the tissue; cross it slowly and large, uneven crystals damage the cell structure. On thawing, the water the tissue cannot hold runs onto the plate as drip loss.
The Codex definition of quick freezing says exactly this: the range of maximum ice crystallisation is passed as quickly as possible, and that range varies between products. The process counts as complete only once the thermal centre, the point that stays warmest, has stabilised at -18 °C or colder.
What sets the rate
Codex names the product's thermal conductivity, thickness, form, starting temperature and production volume. By Plank's equation the freezing rate depends on the thickness of the material, the temperature of the freezing medium and the heat transfer coefficient. Codex also asks for air channels between cartons and pieces; where the load is packed tight, the inner part freezes slowly despite fast air and low temperature.
What to record
The freezer display does not show the product centre. Log core temperature with the time, and put piece thickness and loading on the same form. To compare drip loss, weigh equivalent samples after the same thawing method and note starting mass, final mass, duration and method. For someone buying frozen goods, three questions are enough: at what thickness was the batch frozen, how many hours did the thermal centre take to reach -18 °C, and what temperature was recorded at the freezer exit.
