Freezing system for fragible food products

According to the present invention, apparatus for freezing fragile food products is provided. The apparatus includes a first freezing section which includes a solid conveyor belt which is guided to provide an upper product receiving section and a lower section, which passes through a bath of cryogen so as to chill the surface of the belt. The first freezing section includes means to admit product onto the upper belt section and also includes means to move the product to an exit end of the upper belt section. A second freezing section is provided which is a spiral mechanical or cryogenic freezer. The first freezer has an entry end and an exit end. The entry end of the second freezing section is mated to the exit end of the first freezing section so as to receive product having a bottom frozen surface crust from the first freezing section.

FIELD OF THE INVENTION 
The present invention relates to a freezing system and apparatus for 
freezing food products. More particularly, the present invention is 
directed to a freezing system for freezing fragile food products, such as 
hamburgers and fish fillets. 
BACKGROUND OF THE INVENTION 
Mechanical and cryogenic spiral freezers are well known in the food 
industry. The spiral constructions of these freezers permits relatively 
long freezing surfaces to be contained in a relatively small area. Such 
freezers, however, include a straight entry section which undergoes a 
transition to a circular configuration within the freezer. At the 
transition point the conveyor belt usually undergoes two different changes 
at the same time. The inner section of the belt compresses (collapse's) 
while the outer part expands and the links pull apart. U.S. Pat. No. 
5,141,099 describes an expand only belt. These conditions squeeze or pinch 
the bottom of the food item that is on the inside of the conveyor and also 
makes it stick in the opening of the conveyor belt which damages the food 
item and makes it difficult to release. In contrast, the outside conveyor 
expands and stretches or pulls the food item out of a round shape. Both 
conditions create an undesirable frozen shape which is difficult to stack 
and package. Retaining the round configuration and flat bottom of a meat 
patty is of prime importance to attain proper packaging as well as grill 
to be able to "sear" the surface during cooking. 
Hybrid freezing systems have been proposed, such as that set forth in U.S. 
Pat. No. 5,220,803 to Kiczek. The hybrid freezing system of the Kiczek 
patent mates the outlet of an inversion-type cryogenic freezer to the 
inlet of a spiral-type mechanical freezer. Cryogen vaporizing in the 
immersion unit is directly injected into the mechanical refrigerator where 
the cryogen is in direct heat exchange with refrigerated air circulating 
inside the mechanical refrigerator. 
As shown in FIG. 1 of the Kiczek patent, the product to be frozen is 
dropped through a port into the liquid cryogen and is then carried by a 
conveyor belt through the cryogen bath to the entrance of the mechanical 
freezer. During passage of the food product through the cryogen bath, a 
crust is formed on the product which minimizes or lowers the dehydration 
of the final frozen product. It would not be practical to utilize this 
method for fragile food products such as hamburgers, which need to be 
placed in a certain and fixed relationship to each other on the conveyor 
belt. 
Accordingly, it is a principle object of the present invention to provide a 
freezing system to impart a frozen crust on fragile food products, such as 
hamburgers, prior to introducing the food product into a mechanical or 
cryogenic spiral freezer.

SUMMARY OF THE INVENTION 
According to the present invention, apparatus for freezing fragile food 
products is provided. The apparatus includes a first freezing section 
which includes a solid conveyor belt which is guided to provide an upper 
product receiving section and a lower section, which passes through a bath 
of cryogen so as to chill the surface of the belt. The first freezing 
section includes means to admit product onto the upper belt section and 
also includes means to move the product to an exit end of the upper belt 
section. A second freezing section is provided which is a spiral 
mechanical or cryogenic freezer. The first freezer has an entry end and an 
exit end. The entry end of the second freezing section is mated to the 
exit end of the first freezing section so as to receive product having a 
bottom frozen surface crust from the first freezing section. 
DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the apparatus of the present invention comprises a 
first freezer section 11. Freezer 11 has an insulated housing 12 and a 
product inlet port 13 in the housing for placing product to be frozen onto 
conveyor belt 15. Conveyor belt 15 is driven around rollers 17 and tension 
rollers 19, so as to pass the conveyor belt 15 through a cryogen bath 21. 
The cryogen bath 21 is supplied by cryogen inlet 23 from cryogen manifold 
25. The level of cryogen is controlled by liquid level sensor 24, 
temperature sensor 26 and control valve 28. Vaporized cryogen gas is 
exhausted through cryogen outlet 30. The exhausted cryogen gas may be 
routed through the second spiral freezer 29 to supply part of the freezing 
load for that freezer. 
Conveyor belt 15 is made from a solid material, such as stainless steel, to 
provide a smooth solid surface or may be made from individual metal or 
plastic plates interlocking to form a smooth, solid surface. As this 
conveyor belt is drawn through the cryogen bath, the belt becomes 
extremely cold. Food products such as meat patties are placed on the cold 
belt and are transferred through product outlet port 27 into a second 
cryogen or mechanical spiral-type freezer 29 by means of conveyor belt 31. 
The spiral-type freezer 29 can be any of the commercially known 
spiral-type freezers, such as that described in U.S. Pat. No. 5,020,330 to 
Rhoades, et al., the teachings of which are incorporated herein by 
reference. 
While the conveyor belt 15 may be made of a solid material, such as 
stainless steel, it is preferably made from individual metal or plastic 
plates interlocking to form a smooth, solid surface. A stainless steel 
conveyor belt would be relatively thin and heat transfer to freeze the 
surface of a food product would take place very rapidly. This might result 
in product sticking to the surface. The rollers 17 are the driving rollers 
for conveyor belt 15. For a stainless steel belt, the driving engagement 
is friction between the surface of the rollers 17 and the surface of 
conveyor belt 15. This requires large diameter rollers. The use of 
interlocking metal or plastic plates permits the use of positive 
engagement between rollers 17 and conveyor belt 15 and allows the use of 
smaller diameter rollers 17. 
As the conveyor belt is drawn through the cryogen the plates become 
extremely cold. A food product, such as meat patties, are placed on the 
cold plate and the surface of the product is frozen to provide a crust 
during contact with the conveyor belt surface. This makes the food product 
rigid enough to be transferred into the spiral-type freezer. A scraper bar 
16 is mounted at the exit end of conveyor belt 15 to assist in removing 
product from the conveyor belt. The scraper bar has a very thin knife 
edge. The product slides or moves enough to take the transition turn from 
the straight portion of the internal spiral moving conveyor belt to the 
circular portion of the spiral conveyor belt. This eliminates any damage 
to the food product. The food product can also be placed closer together 
in the spiral-type freezer so as to increase production and efficiency. 
As shown in FIG. 1, a cryogen can also be sprayed by nozzles 33 onto the 
bottom surface of the conveyor belt to provide additional cooling for the 
conveyor belt. Also, as shown in FIG. 1, the top surface of the food 
product can be crust frozen by spraying a cryogen onto the top surface of 
the product from nozzles 35 as it is being transferred along the length of 
conveyor belt 15. 
The use of a solid, chilled conveyor belt in accordance with the present 
invention has numerous advantages over the prior art wherein a surface 
crust is frozen on the product by moving the product through a bath of 
cryogenic fluid. The chilled conveyor belt of the present invention 
permits exact placement of the food product in close proximity. Also, the 
use of a liquid cryogen bath to freeze the product promotes stress 
cracking in many food products, such as meat patties, filled pasta and 
fish fillets.