Food processing method

Meat is processed by introducing it into a mobile cooking vessel after which the vessel is sealed from the atmosphere. A stock liquor is heated by a heat exchanger to a cooking temperature of at least 60.degree. C. and circulated through the vessel and the heat exchanger for a time sufficient to heat and cook the meat. After the meat is cooked, the circulating stock liquor is cooled by the heat exchanger to a temperature suitable to cool the heated, cooked meat to a temperature of no more than 15.degree. C. within 45 minutes.

The present invention relates to a method of processing food, and more 
particularly to a method of processing meat during the preparation of a 
chilled food product. 
BACKGROUND OF THE INVENTION 
The consumer market is constantly changing. Consumers are becoming more 
discerning and have a greater awareness of dietary needs. In particular, 
consumers are increasingly showing a preference for natural foods not 
containing any "artificial" ingredients such as preservatives, stabilisers 
or artificial colouring or flavouring. Fresh food is, therefore, becoming 
more popular than dried, processed or frozen foods. 
Chilled foods are perceived as being fresh and natural, the chilled cabinet 
is one of the fastest growing sectors of the European food market. 
However, a major problem of chilled culinary foods at the present time is 
that, unless they contain added preservatives, the maximum shelf life is 
usually no more than about seven days. 
When one considers that, after manufacture, the life or a chilled food 
usually comprises distribution to a retailer, backof-store chill storage, 
display in chill cabinets, purchase by the consumer, transport home and 
storage in the refrigerator before consumption, a shelf life of seven days 
is extremely short and it would be desirable to have a significantly 
longer shelf life of up to three weeks or more yet without the addition of 
any "artificial" ingredients. 
SUMMARY OF THE INVENTION 
We have found that these objects may be achieved by linking together 
special cooking and pasteurization techniques, and cooling techniques with 
hygienic filling, packing and sealing methods. The filling, packing, and 
sealing can be carried out in an air-conditioned room, known as a 
"clean-room", similar to the type used in the pharmaceutical industry for 
manufacturing such products as enteric feeds. 
In the case of chilled foods containing meat as a constituent, it is 
important for microbiological safety reasons and for sensory quality 
reasons, that cooling of the meat is carried out as rapidly as possible 
after cooking. One way to do this is to carry out the two processes in the 
same vessel. The cooked and cooled meat then has to be transported to the 
filling line in a microbiologically clean fashion. 
We have found that both these requirements can be achieved by a processing 
method which involves the use of a special mobile, recirculation process 
vessel. 
Accordingly, the present invention provides a method of processing meat 
characterized in that the meat is introduced into a mobile cooking vessel, 
the vessel is sealed and adjusted to superatmospheric pressure using an 
air/steam mixture or an inert gas, a stock liquor is passed through a heat 
exchanger to raise its temperature to at least 60.degree. C. and 
circulated through the vessel and heat exchanger for a period of time 
sufficient to heat up, cook and pasteurise the meat, substantially 
immediately after which the circulating stock liquor is cooled by the same 
heat exchanger to a temperature suitable for cooling the meat to 
15.degree. C. or below within a maximum time of 45 minutes. 
DETAILED DESCRIPTION OF THE INVENTION 
Any animal meat may be processed by the method of the present invention, 
for example, beef, pork, lamb, mutton, veal, poultry or game. The method 
is particularly valuable for chicken, diced beef or pork fillets. 
By a mobile cooking vessel we mean any cooking vessel capable of being 
transported either by hand or mechanically in a closed state while 
containing the cooked and cooled meat. For example, the vessel may be 
provided with wheels. 
Before being introduced into the vessel, the meat is prepared into pieces 
of a size appropriate for the final product and the surface and shape of 
the meat pieces are set, conveniently by surface frying, for instance, at 
120.degree. C.-200.degree. C. for a short time (40 to 120 seconds) or by 
grilling, blanching in hot water or heating in hot air. 
After the meat has been introduced into the vessel, the vessel may be 
sealed by conventional means and pressurised to a pressure conveniently 
from 0 to 4 atmospheres and preferably from 1/2 to 1 atmospheres. The 
atmosphere used may be air, steam or a mixture of steam and air, but if 
desired, other food acceptable gases may be used, for example, nitrogen, 
carbon dioxide, helium or nitrous oxide or convenient mixtures of these 
gases. The use of oxygen-free gases, especially nitrogen, improves the 
flavour of the cooked meat and helps to reduce any warmed-over flavour 
which may occur after prolonged storage of the final chilled product. 
Warmed-over flavour is characteristically often found with cooked, stored 
and re-heated meats. 
The stock liquor may be any conventional stock solution or cooking medium 
in which the particular meat product could be cooked. 
The heat exchanger used in the method of the invention is preferably a 
plate heat exchanger. When the heat exchanger is used to raise the 
temperature of the stock liquor, it is conveniently heated by hot water or 
steam, under pressure if necessary. When the heat exchanger is used to 
cool the stock liquor, it is conveniently cooled by chilled water or a 
cryogenic liquid, for instance, liquid NH.sub.3, liquid CO.sub.2, liquid 
SO.sub.2, or possibly directly evaporated Freon. 
The stock liquor, which is conveniently stored in a stock tank, is 
advantageously pumped through the heat exchanger, for instance, by a 
standard centrifugal pump, or, alternatively, a piston pump may be used to 
circulate it through the vessel. Preferably, the stock is pumped upwards 
from the bottom of the vessel, and removed from the side at a point near 
the top, though it may be sprayed from the top of the vessel and removed 
from the base, to heat up and then cook the meat by flowing around the 
meat pieces. 
The heating up to the cooking temperature, which is taken as the centre 
temperature of the meat pieces, usually takes from about 15 to 45 minutes, 
preferably from 20 to 30 minutes. The cooking is conveniently carried out 
for a period of from 5 to b 60 minutes depending upon the type of meat and 
the size of the meat pieces. The cooking temperature depends on the type 
of meat used, but is usually from about 60.degree. C. to 110.degree. C. 
If desired, provision may be made for circulating other marinades through 
the vessel in addition to the stock solution. If desired, provision can be 
made for supplying a suitable food grade gas to the headspace of the 
vessel during the heating and cooking sequence. 
Immediately after the cooking step, the heating fluid in the heat exchanger 
is replaced by a coolant, so that the circulating stock liquor is cooled 
sufficiently to cool the meat to below 15.degree. C. and preferably below 
10.degree. C. within 45 minutes. During cooling, a sterile gas is used to 
pressurise the vessel. For example, this may be done by passing it through 
a presterilised air filter. 
When the meat has cooled to the required temperature, the stock liquor is 
pumped out of the vessel, conveniently back to the stock tank and the 
vessel is disconnected from its back-up plant and transported to a packing 
room via a surface cleaning system, for example, an alcohol spray, to 
sterilise the surface. Preferably, the vessel remains under pressure after 
it has been disconnected from its back-up plant. This may be achieved by 
means of stop valves which form part of the vessel and are closed before 
any disconnection thus maintaining pressure within the vessel. Means may 
also be provided for topping-up the pressure within the vessel after 
disconnection in case of a leak. The vessel may also be provided with 
automatic pressure relief before the lid can be opened. 
In the filling room, the vessel is opened, the meat is removed and filled 
into packages, if desired, together with other pasteurized ingredients or 
garnishes, after which the packages are hermetically sealed and chilled 
rapidly, for instance, by blast chilling, usually to a temperature less 
than 4.degree. C. over a maximum period of 90 minutes. 
Such chilled products containing meat processed by the method of the 
present invention may have a shelf life of three weeks or more. 
The present invention also provides a mobile cooking vessel which comprises 
means for sealing, pressurizing, and then circulating a stock liquor 
through the vessel and a heat exchanger. 
The vessel of the present invention is preferably of a size which enables a 
food product to be introduced and removed by hand and may be provided with 
one or more removable mesh grids on which the food product may be placed. 
A plurality of mesh grids serve as separators which enable the meat pieces 
to be arranged in layers and thus prevent the meat layers from compacting 
and hence ensuring an even temperature distribution within the vessel. 
Preferably the vessel is of a size which allows it to be transported by 
hand and may conveniently be provided with wheels. 
If desired, in addition to the means for circulating the stock liquor, the 
vessel may be provided with means for circulating other marinades in order 
to obtain desired flavour characteristics. 
The vessel may also be provided with means of pressurising it with air or 
other gases. 
The present invention is further illustrated by way of example with 
reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to the drawings, the system comprises a mobile process vessel 10 
provided with removable mesh grids 11, a temperature probe 12, feed pipes 
13,14, and a lid 15 provided with a feed pipe 16 having a valve 17 and 
sterile air filter 18. Feed pipe 13 is provided with valves 19,20, a 
thermostat 21 and a heat exchanger 22 fitted with an inlet pipe 23 for 
steam or cooling water as desired (the outlet pipe is not shown), while 
feed pipe 14 is provided with valves 24,25, a pump 26 and a filter 27. A 
reservoir 28 is connected via a valve 29 to the heat exchanger 28 and the 
filter 27. 
In operation, referring to FIG. 1, the mobile process vessel 10 is 
sterilised using water at 125.degree. C. and then manually loaded with 
chicken pieces which have previously been passed through a fryer to 
surface fry in shallow cooking fat at 125.degree. C. The chicken pieces 
are loaded in layers on the mesh grids 11. The temperature probe 12 is 
inserted into the centre of one of the pieces of chicken. Stock solution 
from the reservoir 28 is poured into the open vessel 10 until the chicken 
pieces are covered. The lid 15 of the vessel 10 is then shut and clamped 
down. 
Referring now to FIG. 2, stock is then pumped by pump 26 from the vessel 10 
through the filter 27 and then the heat exchanger 22 and back to the 
vessel 10. Steam is introduced through inlet pipe 23 into the heat 
exchanger thus heating up the stock until it has reached the control 
temperature recorded by the thermostat 21. The stock circulates raising 
the temperature of the chicken pieces and when the temperature probe 12 
reaches the predetermined cooking temperature of 90.degree. C after about 
25 minutes, the cooking starts. In the meantime, steam is passed through 
the air filter 18 in order to sterilise it. The cooking time is 15 
minutes. 
Referring to FIG. 3 after the cooking has finished the steam supply through 
the air filter 18 is shut off and compressed air is passed through the 
filter 18 and valve 17 to the vessel to pressurise it to about 0.5 
atmosphere. In addition, the steam supply through pipe 23 is turned off 
from the heat exchanger 22 and replaced by a supply of chilled water at 
2.degree. C which cools the stock to 5.degree. C. and hence the chicken 
pieces to 10.degree. C. in 45 minutes. Once the temperature probe 12 
reaches the pre-determined cooling point the pump shuts down. 
Referring to FIG. 4, the stock is then pumped back into the reservoir 28 
and the valves 19,20,24,25 and 29 are closed. The vessel 10 is then 
uncoupled and wheeled through an alcohol spray unit to sterilise its 
exterior surfaces and into the packing room. 
In the packing room the vessel is opened and the cooked chicken pieces are 
placed in a plastic tray, and other components added before the tray is 
hermetically sealed and chilled to 3.degree. C. in 60 minutes by means of 
a blast chiller.