Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THF IMV~NTION
Field of the Invention
This invention relates to a novel method of dr~ing
meat which comprlses deep-frying the meat under reduced
pressure and then vacuum freeze-drying the deep-fried meat
and, if desired,Ereheating the meat prior to -the above deep
frying treatment.
Brief Description of the Prior Art
In the past, several techniques for drying food-
stuff have been studied and developed. The object of thesemethods is to dry the foodstuff without impairing its inherent
characteristics and to make it possible to rehydrate the dried
foodstuff into an appro~imately similar state to that of the
oodstuff before drying. At present, it is generally accepted
that among the various drying techni~ues, the freeze drying
technique best attains the above objects. The freeze drying
technique is used to dry many foodstuff and, of course~ to
dry meat.
The meat is freeze-dried in such a way that almost
none of its cells are broken and the meat does not shrink,
so that the appearance of the meat after drying is substan-
tially the same as before drying. In the freeze-dried meat,
however, the flavor-bearing materials in the meat, e.g. the
meat juices and the lil~e, are present in the form of powder,
and ~Jhen the meat is rehydratèd, the powdered flavor-bearing
materials are dissolved in water or a seasoned broth which
penetrates into the dried meat and are extracted from the
meat. ~s a result, the rehydrated meat loses ~lavor.
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Moreover, the state of the rehydrated rnéat differs from tha~
of the meat before drying, and the rehyclrated meat i~
obtained by merely allowing the water or seasoned broth to
impregnate in the freeze-dried meat. Thus, the taste and
texture of the meat which has been rehydrated and then cooked
is different from the taste and texture of fresh (undried)
meat which has been cooked.
As mentioned above, the dried meat obtained accord-
ing to the conventional freeze drying technique may be
satisfactory in appearance. However, when rehydrated and
cooked, its flavor and texture do not compare satisfactorily
with undried meat which has been cooked.
For example, USP 3,984,577 discloses a method of
producing a compacted, freeze-vacuum-dehydrated food selected
from the group consisting of vegetables and meats which upon
rehydration with water produces a rehydrated food which is
substantially indistinguishable from the food prior to compac-
tion and freeze-vacuum-dehydration thereof. This method
comprises compactincJ said food while frozen in particulate
form and simultaneously freeze-vacuum-dehydrating said food
to a moisture content below about 4.0 % by weight, said
- compacting being carried out by applying mechanical pressures
- of at least about 20 p.s.i. and sufficient to provide a
freeze-vacuum-dehydrated food having a bulk density of from
about 0.5 to about 1.2 g/cc. However, the drying method in
the above U.S. Patent is merely a vacuum freeze-drying.
Accordingly, the dried meat obtained according to the method
of the above patent has similar defects to the conventional
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freeze-drled meat. Mamely, upon rehydration ,lith water, tnP
powdered flavor-bearing materials, e.g. the meat juices, in
the dried meat are dissolved in water which penetrates into
the meat and are extracted from the meat. Thus, the re-
hydrated meat loses flavor.
SUM~R~ OF THE INVENTION
This invention obviates the above defects of the
meat obtained according to the conventional vacuum freeze-
drying technique. The object of this invention is to providea method for drying meat to obtain dried meat which after
rehydration and cooking is substantially identical to cooked
fresh meat in flavor and texture and which is not make
unpalatable by breaking of the meat tissue under a high
temperature and pressure treatment, such as a retort treat-
ment. The gist of this invention which attains the above
object resides in a method for drying meat which comprises
predrying the meat by deep-frying it under reduced pressure
and then freeze-drying the prèdried meat under vacuum.
DESCRIPTION OF THE INVENTION INCLUDING THE PREFERRED
~ - EMBODIMENTS
- The typical meats to which this invention can be
applied are those of such domesticated animals as the clow,
pig, sheep, goat, horse, rabbit etc. a~d those of such wild
animals as the kangaroo, deer, wild boar etc., as well as
those of the chiken and whale. They may be used in any of
various cut shapes or in the form of processed meat such as
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3~
minced meat for use as a raw material for ~am, sausaye,
ha~burger and the like.
According to this invention, the above meat is
predried by deep-frying it under reduced pressure and pre-
ferably the meat is preheated prior to the predryingtreatment. The preheating treatment is a preferable means
for realizing evaporation of water from the meat during its
predrying in the succeeding step, i.e. the deep frying step
under reduced pressure. If the temperature throughout the
meat is made uniform prior t.o deep-frying under vacuum, it
becomes possible to cause the uniform evaporation of water
from the meat during the deep frying treatment under reduced
pressure. The preheating in this invention, therefore,
functions as a temperature conditioning treatment in order
to make the temperature throughout the meat approximately
uniform. `
In order to attain the effect of the above temperature
conditioning treatment, the preheating is preferably carried
out at a temperature of about 30 to 90C. Moreover, so that
the preheating will causes approximately uniform thermal
modification to some extent, it is preferable to carry out
the preheating at a temperature of about 50 to 85C. By this
heat induced modification, the flavor-bearing materials, e.g.
the meat juice component, in the meat can be solidified and
thus the flavor of the meat can be locked in. This is an
important feature of this invention which is not observed
whatsoever in the case of the conventional freeze drying
technique. The preheating may be executed by an appropriate
5 _
means such as a hot-air -treatment, a steaming trea~ment, a
constant tempe~ature-humidity treatment or the like. The
succeeding predrying step is a deep rying step and for this
a preheating step of immersing in heated oil is preferable.
The preheated meat is predried by the succeeding
deep frying treatment under reduced pressure. Effects of
the deep frying treatment under reduced pressure are mainly
(1) that an appropriate dehydration and thermal modification
occur relatively rapidly throughout the meat at a low tem-
perature and in a short time, whereby the flavor-bearing
materials of the meat are solidified and locked in; (2) that
an appropriate amount of oils and fats are forced to penetrate
the meat tissue; (3) that the growth of ice crystals in the
succeeding freezing step is prevented; and l4) that the drying
time at the freeze drying operation is shortened.
The above effects are important features of this
invention which were not at all found in the conventional
freeze drying technique.
In order to efficiently realize the effects of the
predrying treatment according to the deep frying treatment
under reduced pressure, it is preferable to use a high degree
of vacuum and to reduce the pressure to the desired degree
~of vacuum rapidly, and to use a low oil temperature. Although
the concrete conditions vary somewhat depending on a kind,
size, amount and the like of the meat to be treated, the
pressure is generally not more than about 100 torr and pre-
ferably not more than about 50 torr. The time for attaining
the desired degree of vacuum is not more than a~out 5 minutes
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and preferably not more than about 2 min~tes. Tne oil tempera-
ture is pre~erably not more than about 100C and more preferably
about 50 to 85C. In the case that the preheating is carried
out by the exposure to oil before the predrying treatment, it
S is preferable from the point o workability ~o~carry out the
predrying at the approximately same oil temperature as that of
the preheating.
There are various methods for carrying out the pre-
drying by deep-frying the meat under reduced pressure. For
example, there are a method comprising immersing the meat in
oil in an oil tank and then rapidly reducing the pressure
throughout the oil tank~ and a method comprising reducing
the pressure throughout the oil tank beforehand and then
immersing the meat in oil, the meat being supplied to the
oil`tan~ before or after the pressure reduction. The predry~
ing due to the deep frying under reduced pressure according
to this invention can be carried out by either method.
However, in the case that the preheating is carried out by
immersing the meat in the heated oil prior to the predrying,
the former method is preferred in view of the advantages that
the preheating and the predrying can be carried out in ~he
same vessel and that the tem~erature of the meat after pre-
heating does not vary.
The water content of the meat which is obtained
by the predrying is generally about 35 to 65 % and preferably
about 45 to 55 %, based on the weight of -the meat exclusive
of the fat portion. If the ~ater content of the meat is not
lowered to this level by the predrying, the effects of the
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predrying as mentioned above may not be substantially produced
and thus, there may be little difference in quality between
the finally obtained dried meat product in this invention and
the meat product obtained by the conventional freeze-drying
technique. On the other hand, in the case that the water
content of the meat is excessively lowered by the predrying,
hardening and shriveling of the meat tissue starts-to become
remarkable because of the evaporation of a large amount of
water, and this is apt to damage the appearance of the meat
and to lower its efficiency of rehydration with water or
seasoned broth.
The meat predried by the deep frying treatment under
reduced pressure is finally processed into the dried meat
product by the vacuum freeze-drying treatment. The vacuum
freeze-drying treatment may be carriecl out by a conventional
procedure, and it is preferable that the final freezing
temperature be not more than about -10C and the cooling rate
be, for example, in such that the cooling time from 25C to
-30C is about 30 to 120 minutes.
The heating means in the vacuum freeze-drying step
may be either by heat conduction, radiant heating, internal
heating or the like, or a combination thereof. The freeze
drying should be preferably carried out as rapidly as possible
in such a way that the temperature of the dried portion of
the meat is not over about 70C and the ice crystals in the
undried portion do not melt.
Below are described comparative tests demonstrating
the effect of the method of this invention, and examples of
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this invention. These are presented for explanatory purposes
and are not to be considered as limiting the invention in any
way.
Comparative Test 1
(1) This Invention A
Beef round sliced to a thickness of 3 to 5 mm was
predried by deep-frying it in salad oil at 50C under a reduced
pressure of 5 torr for 5 minutes. Then,the meat was prefrozen
to -35C at the rate of -1C/min. and thereafter was vacuum
freeze-dried with radiant heat of 60C under a reduced pressure
of 0.5 torr for 3 hours to obtain dried meat having a water
content of about 3%. Then, the resulting dried meat was
immersed in water at room temperature until the dried meat
was sufficiently rehydrated, and thereafter the rehydrated
meat was put in a hot butter-greased frying pan and was cooked
atweak caloric force for about one minute and 30seconds.
(2) Comparative Example 1
Beef round sliced to a thickness of 3 to 5 mm was
cooked in a frying pan under the same conditions as in "This
Invention A".
(3) Comparative Example 2
Beef round sliced to a thickness of 3 to 5 mm was
prefrozen under the same conditions as in "This Invention A"
and thereafter it was vacuum freeze-dried for 8 hours under
the same conditions as ln "This Invention A" to obtain dried
meat having a water content of about 3%. Then, the dried meat
was rehydrated and cooked under the same conditions as in
"This Invention A".
Table 1 shows the results of the above comparative tests.
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Table I
This Invention A Comparative Example 1 Comparative Example 2
State of dried meat Light brown. Slightly reddish light brown.
Held shape well. Disintegrated easily.
Rehydration time 30 minutes - 20 minutes,.
State of Immersion Immersion water became Immersion water became
water and re- slightly reddish but - reddish with time.
hydrated meat almost no charge. Rehydrated meat lost red-
Color of rehydrated ness with time.
~ meat was substantially
the same as that of
raw meat.
State of cooked meat Almost exactly the same Redness observed in Shrank easily; difficult t~g
as cooked raw meat. the center portion. cook.
Cooked a little more Only the surface burned
, quickly than raw meat. easily.
Flavor and texture Hardly any different Appetizing. Unpalatable and soft.
of cooked meat from cooked raw meat. Juicy. Lacking flavor and texture.
Juicy. Not juicy.
Left a bad aftertaste.
f:~
From the above Table I, -the foilowing observations
can be made. Comparing the states of the dried beef in Table
I, it is clear that the dried beef obtained by "This Invention
A" is less apt to disintegrate than the dried beef which ~as
obtained by the conventional freeze-drying technique (Compara-
tive Example 2) and thus that reduction of product yield by
breaking and the like is effectively prevented in the case of
this invention. The rehydration time in "This Invention A"
is slightly longer than that of "Comparative Example 2". In
"Comparative Example 2", the flavor-bearing materials contained
in the dried beef are extracted from the beef and the immersion
`water become remarkedly reddish, and on the other hand, in
"This Invention A" such phenomena are almost non-existent and
the dried beef can be rehydrated in such a state that~the
flavo -bearing materials are retained. These differences are
remarkedly reflected in the state of the beef during cool;ing
and the flavor and texture of the cooked beef. Namely, in
"Comparative Example 2", the beef easily shrinks during cook-
ing and burns only on the surface thereof. This means that
the meat rehydrates faster but is apt to release water after
rehydration and during cooking. As a result, the taste and
~ texture of the cooked beef becomes unpalatable and it i5 not
juicy. Moreover, the poor flavor of the cooked beef is made
even worse by the fact that the flavor-bearing materials of
the beef are eluted during rehydration.
On the other hand, the rehydration in "Thls Invention
A" is slower than that in ''Comparative Example 2" but the
state of the beef during cooking is a-~most the same as that
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of raw béef during cooking. Thus, the rehydrated and cooked
beef is almost no difrerent in taste, texture and juiciness
. . .
from cooked raw beef. In addition, in "This Invention A",
an appropriate amount of oils and fats is present in the beef
because of the deep frying treatment under reduced pressure
and thus the taste and texture of the cooked beef are mellowed
by the pressure of the oils and fats. Moreover, the flavor
of the rehydrated and cooked beef is almost the same as that
of the cooked raw beef since almost no flavor-bearing material
is eluted during rehydration. In addition, "This Invention A"
produces the excellent effect that the freeze-drying time of
the beef is only about one third as long as "Comparative
Example 2".
Comparative Test 2 -
(1) This Invention B
The beef round which was rehydrated in the above"This Invention A" was, without being cooked~ placed in a
retort pouch together with a curry roux and thereafter was
subjected to a retort treatment at 121C for 8 minutes. 30 g
of rehydrated beef round and 150 g of the curry roux were
used in this experiment, and also in the following comparative
~ examples.
-(2) Comparative Example 3
Raw beef round was placed together with a curry roux
into a retort pouch and thereafter was subjected to a retort
treatment under the same condition as in the above "This
Invention B".
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(3) Comparative Example 4
The beef round, which was cooked in the above
. .
"Comparative Example 1", was placed together with a curry
rQux i,n a retort pouch and thereater was sub'jected to a
retort treatmen-t under the same condition as that in the
above "This Invention B".
(~) Comparative Example 5
The beef round, rehydrated in the above "Comparative
Example 2" was, without being cooked, placed together with a
curry roux in a retort pouch and thereafter was subjected to
the retort treatment under the same condition as that in the
above "This Invention B".
(5) Comparative Example 6
The beef round, cooked in the above "Comparative
Example 2", was placed together with a curry roux in, a retort
pouch and thereafter was subjected to the retort treatment
under the same condition as that in the above "This Inven-tion
B".
The retort curry, which was obtained according to
each of the above methods,was heat-treated in bolling water
for 4 minutes and then a panel of tasters are the curry to
carry out an organoleptic test regarding the taste and texture
of the beef round. In the organoleptic test, a 10 point-
scoring method was used wherein the best score was 10 and
the worst score was 1. Table II shows the results of the
above test.
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l;~V~
Table II
Organo-
leptic Brief Comment
Score
5 This 10 Fibrils intact and there was an
Invention B appropriate resistance to the teeth.
Juicy.
Comparative 8 Slightly unpalatable compared with
Example 3 "This Invention B".
Slightly lacking in juiciness.
Comparative g P~elatively good taste and textuxe but
Example ~ fibrils weaker than in "This Invention
B".
Comparative 6 Soft but fibrils weak and resistance
Example 5 to the teeth was bad.
Lacking in juiciness.
Comparative 8 Fibrils stronger than those of "Com-
Example 6 parative Example 5" and resistance to
the teeth was good, but inferior to
"This Invention B".
In the case where the meat such as beef is heat-
treated at high temperature and under high pressure (e.g. in
a retort treatment), generally the fibrils tend to become
weak and the taste and texture of the treated meat tends to
become bad. As is clear from the above Table II, however,
~ in the case where the dried meat obtained according to the
method of this invention was rehydrated and was then subjected
to the retort treatment, almost no degradation in the taste
and texture of the type mentioned above was observed and the
treated meat possessed an appropriate resistance to the teeth
and good taste andtexture.
As mentioned above, the dried meat obtained according
to the method of this invention retains the flavor-bearing
materials, such as the meat juices and the like, in a
solidified and locked state. Thus, when the dried meat is
rehydrated and then cooked, the flavor and teYture of the
cooked meat are almost the same as those of cooked raw meat.
~loreover, this invention also has the advantag~ that the
tissue of the meat is not disintegrated by high-temperature
and pressure treatment (such as the retort treatment) and
thus that the taste and texture of the meat do not become
bad. Furthermore, according to this invOntion, wafer
contained in the meat is removed to some degree by the pre-
drying treatment. This invention has, therefore, the
advantage that the freeze-drying treatment in this invention
can be conducted in a very short time as compared with the
freeze-drying time in the prior art and the advantage that
it is possible to reduce the damage to the tissue of the
meat which is caused by ice crystals formed at the time of
the prefreezing before the freeze-drying treatment.
E~ample 1
1000 g of lamb (water content of about 75~) sliced
to a thickness of 3 to 5 mm and an area of about 30 to 50 mm
~ x about 50 to 70 mm were placed in an oil tank containing a
corn salad oil at 50C and then were immersed in oil for 10
minutes to be preheated. Then, the pressure throughout the
oil tank was reduced to 10 torr in about one minute and the
predrying treatment was carried out by deep-frying the pre-
heated lamb under the reduced pressure for 2 minutes.
Thereafter, the oil was drained from the lamb and the pressure
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2~
in the tank was returned to normal in about 3 minutes and
the lamb slices was withdrawn. The resulting lamb slices
weighed about 800 g and the water content thereof was about
55%.- Then, the lamb slices was prefrozen under a freezing
condition of about -1C/min. until the final temperature of
the lamb product reached -30C, which was followed by a
vacuum freeze-drying treatment under 0.5 torr. The heatiny
was carried out on a radiant shelf. The vacuum freeze-dry-
ing treatment was carried out at a radiant shelf temperature
of 60C and in a drying time of 3.5 hours to obtain about
400 g of dried lamb slices having a water content of not
more than 3%.
Then, about 400 g of the resulting dried lamb slices
were immersed in water of 25C for 30 minutes to allow the
water to impregnate the meat, whereafter the rehydrated lamb
slices weighed about 630 g. Thereafter, the rehydrated lamb
was cooked in a butter-greased frying pan to obtain about
500 g of the saute lamb. The flavor and texture of the sauté
lamb were similar to those of raw slices of lamb cooked in a
greased-frying pan and seemed to smell somewhat less strongly
and to taste better.
Example 2
.
1000 g of minced beef (water content of about 60%)
were placed in an oil tank containing a 2 to 1 mixture of
corn salad oil and tallow at 50C. Then, the whole oil tank
,~as reduced in pressure to 5 torr in about one minute. After
the pressure reduction was completed, the minced beef was
immersed in the oil to be subjected to the predrying treatment
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by deep-frying it under the reduced pressure for 3 minutes.
Thereaf-ter, the oil was drained from the meat, the pressure
in the tank was returned to normal in about 3 minutes and
the minced beef was withdrawn. The resulting minced beef
weighed about 800 g and the water content thereof was about
55%. Thereafter, the prefreezing treatment and the vacuum
freeze-drying treatment were carried out according-to the
same procedure as in Example 1 to obtain about 355 g of
dried minced bee having a water content of not more than 3~.
Then, about 355 g of the resultant dried minced
beef were immersed in water of 25C for 20 minutes to allow
the water to impregnate the meat. There was obtained about
770 g of rehydrated beef. The rehydrated minced beef was
kneaded in a container, formed into about 3 cm balls and
fried in an oil at 170C for about 2 minutes to obta~in mince-
meat balls. The flavor and te~ture of the obtained mincemeat
balls were somewhat similar to those of mincemeat balls made
directly from raw minced beef. The former mincement baLls
heated up faster than the latter ones,~making them easier
to cook.
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