According to Michael Newman, manager of equipment development for BOC's Process Gas Solutions, Food Group, the new cryogenic freezer differs from earlier impingement freezers in its ability to combine high-velocity airflow with atomized liquid nitrogen to produce "a continuous, consistent uniform freezing not found in mechanical impingement freezers."
Newman said that when the system was tested on a variety of bakery products, including cookie dough, pizza dough and pastry dough, dehydration loss was routinely well below the loss rate usually found in a conventional tunnel freezer. "And because the impingement freezer runs at a much colder temperature than a mechanical freezer, you can achieve higher production rates in a smaller floor space."
The impingement freezer produces extremely high convective heat transfer along with efficient use of cryogen to produce a continuous, consistent uniform baking across and along the belt from both top and bottom surfaces. Upon entering the freezer, the surface of the food product is instantly crust-frozen with a liquid nitrogen spray and high-velocity nitrogen gas, thereby trapping product moisture and resulting in a higher yield.
As the product continues along the belt, it is impinged from above and below with high-velocity nitrogen gas. Maximum process efficiency is achieved by moving and warming the nitrogen gas as it travels with product flow down the length of the freezer.