A special brine formulation is prepared which, when cooled to -40 degrees C, forms many complex crystals. Product, fish in this example, is vacuum packed and placed in the brine. The brine flows over, under and around the product. The brine absorbs the heat of the product by changing the state of crystal to liquid. The brine looses crystal density as it passes over, under and around the product.
The product becomes frozen quickly, forming simple crystals quickly enough so that there is minimal differential between the time it takes to freeze inside and outside the individual cells, preventing any damage and thereby minimizing purge. This happens progressively from the initial point of contact with the brine and from the outside (that area first in contact with frozen brine crystals) to the inside of the product.