Multi-channel cooling die

Details Multi-channel cooling die Multi-channel cooling die

2002-11-07

2004-11-16

Heitbrink, Tim (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Stock pressurizing means operably associated with downstream...

Including heating or cooling means

C425S38200R, C425S464000

Reexamination Certificate

active

06817858

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to cooling dies for use in association with food extruders in the manufacture of texturised protein food products, and a perforated die plate for use at the cooling die outlet.
In particular, the present invention relates to a cooling die for use in the manufacture of an extrude food product that has the appearance of fibrous meat pieces such as fish, chicken, lamb or beef. The cooling die is attachable to the outlet of an extruder which may contain one or more screws and feeds molten extrudate to said cooling die at a temperature between 110° and 180° C.
BACKGROUND OF THE INVENTION
Various protein texturisation processes have been used for some time in the manufacture of various food product, such as in the manufacture of sausages, cheese curds, mozzarella processed cheeses, bakery products, tofu, kamaboko, meat analogs and seafood analogs. A fibrous texture may be obtained by various means, including extrusion cooking at low moisture levels (typically 10-30% by weight).
Extrusion cooking at high moisture levels (e.g. typically 30 to 80% water by weight) is a relatively new technique which is finding use mainly in the field of texturisation of protein food products.
High moisture extrusion cooking has been discussed as a means of restructuring various natural protein sources, such as fish mince, surimi, de-boned meats, soy flours, concentrates, cereal flours, dairy proteins and the like, in order to obtain cohesive fibrous or lamellar structures (e.g. see “New Protein Texturisation Processes by Extrusion Cooking at High Moisture levels” by J C Cheftel et al, Food Reviews international, 8 (2), 235-275 (1992) published by Marcel Dekker, Inc.).
Unlike low moisture extrusion cooling, high moisture extrusion cooking requires the use of cooling dies for cooling, gelling and/or solidifying the food product issuing from the food extruder. A cooling die dissipates the thermal and mechanical energy accumulated in the food mix, increases the viscosity of the mix, and prevents product steam flash at the die outlet
The concept of extruding cereal, meat or other protein blends at high moisture through an extruder and then passing the extrudate through an attached cooling die, so that product exits the cooling die at temperatures not exceeding 100° C. (typically about 80° C.), is not a new one. This cooling of the product is quite important in order to eliminate expansion of said product as a consequence of steam flashing, amongst other things. There are numerous patents and articles discussing this subject, including discussions of die design in particular.
It is understood that texturisation of the protein food product takes place during cooling as a result of lamellar flow in the die.
Three main types of cooling dies are known for use in this field of technology/application. Most commonly known are elongated rectangular cooling dies. A rectangular cooling die has a long rectangular prismatic housing in which is received a rectangular duct extending along the length of the die. The regions surrounding the rectangular cavity (duct) are cooled with water thereby enabling the extruded food product passing through to be cooled. Cooling dies may also be cylindrical with an internal cylindrical cavity extending along the length thereof. Such a cooling die functions in much the same manner as a rectangular cooling die. There are annular cooling dies in which the internal cavity has an annular cross-section defined by an inner core and an outer cylinder. The inner core and outer cylinder are cooled, thereby enabling the food product passing through the cavity to be cooled.
One problem with known cooling dies is that, as portions of the food product come in contact with the coded surfaces of the die, these portions become thicker, tend to stick to the surface of the die and slip at a lower rate than internal sections of the product Accordingly, velocity gradients and shear forces develop which may cause inconsistencies in the food product and problems with the smooth continuous operation of the cooling die and extruding apparatus. This is a particular problem where the dimensions of the cooling die cavity (e.g. height, width and/or length) have been increased so as to achieve greater throughput of extruded products.
Another problem with known cooling dies is that they effectively cause a “bottle-neck” in the extrusion process. Typically, the capacity of a commercial cooling die is about 100 kilograms per hour, so that product output is limited to this value.
Whilst this extrusion rate has been found to be desirable in order to achieve a commercially acceptable product, it is desired to have greater product output rates to increase yields. The production of high moisture extruded products at manufacturing outputs of up to 200 kg/hr using single channel cooling dies has also been documented. However, extruded products manufactured at these rates tend to be of lower quality and/or consistency than those manufactured at lower rates. Production rates in excess of 200 kg/hr are much more difficult to achieve, due to the physical limitations of known cooling die designs.
The output of a cooling die is determined by a multitude of factors, one major factor being the capacity (of volume) of the cooling die cavity (or channel) which is determined by the cross-sectional area and the length of the die cavity, it increased production rates are required, one has the choice of increasing the cross-sectional area or die length or both. This strategy however may be limiting. For instance, the cross-sectional area of the die cavity is largely determined by the desired product characteristics. Also, increasing the cross sectional area would typically increase the amount of time required to cool the product. It may result in inconsistencies in the product due to the outer portions of the extruded product cooling much faster than the inner portions. Altering the die shape may give a product not meeting desired visual parameters. Increasing the length of the cooling die also has limitations due to the fact that the pressure drop along the die is proportional to the length of the die. Increasing the pressure drop along said cooling die will decrease output of the die or require increased extruder capabilities.
Attempts have also been made to increase the capacity of cooling dies through the use of higher flow rates with cooling dies of greater cross-sectional areas. This measure necessitates longer cooling dies. This has a number of adverse consequences. For instance, longer cooling dies increase the likelihood of inconsistencies arising in the food product and structure blockages occurring in the cooling die. Also, such dies obviously take up more area or floorspace of the production plant, which in turn increases costs.
Japanese patent application No. 4-214049 (publication No. 6-62821) discloses a multi-channel cooling die which is used in the extrusion of thin, thread-like food products from high moisture content proteinaceous raw materials. The cooling die is essentially constructed like a typical shell-and-tube heat exchanger, wherein the shell covers at the axial ends of the cylindrical shell are replaced with purpose built end plates. The inlet end plate is flanged to the extruder's die plate holder, while the other end plate is similar in layout to the stationary tube sheet of the heat exchanger, i.e. a multiple-orifice plate in which the ends of the plurality of inner tubes are wedged and supported.
The plurality of thin-walled inner tubes employed in such typo of cooling die ensure efficient cooling at higher through-put rates of extrudate. It is said that the individual tubes possess high pressure resistance thereby enabling processing of greater amounts of raw materials as compared with conventional, single cavity cooling dies.
One serious shortcoming of such type of cooling die is the need to use “pigs” or long rods for cleaning the individual inner tubes through which the extrudate flaws during processing. The smooth surface of the tubes can be damaged du

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