Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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71429-2
DRIED MUSHROOMS AND A DRYING METHOD THEREFOR
Mushrooms will change in appearance and chemical composi-
tion with time, resulting in lowered trade valueO As to the
change, mushrooms are subject to putrefaction by bacteria,
autodigestion by various enzymes, and chemical attack by
oxygen or other gases in air, sunlight, heat, moisture,
etc.
Against these causes, various methods for storage have
been made available. Typical methods for storage are the
method for storage by sterilization embodied by canning,
bottling, salting, etc., that by suppression embodied by
freezing and carbon-dioxide sealing, and that by drying,
embodied by sunlight and fire dryings, etc.
The method for storage by sterilization has a disadvantage
that both flavor and original color will be lost. Salting
leads even to loss in original taste. Thus, the method for
storage by sterilization should be regarded as a means for
emergency effective merely for preventing putrefaction for
long-term preservation. This method, when applied to mush-
rooms such as Tricholoma Matsutake (ITO et IMAI.) SIMG.
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and Tricholoma ponderosum (PECK.) SING. with which flavor
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and appearance are important, leads to loss in trade value.
The suppression storage via freezing or carbon-dioxide
sealing has various problems in that mushrooms which are raw
are heavy, are inconvenient to transport from producing to
consuming districts, and are apt to deteriorate during
transportati`on.
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The sunlight or fire drying method, though in wide use
for the storage of Lentlnus edodes (BERK.l SING., has a dis-
advantage that oxidation, discoloration, contraction, deforma-
tion, and flavor loss occur.
Another method called rapid freeze drying has recently
been made available as a drying method for materials to be
added to instant foods. This method of rapid freeze drying
was tested for its applicability to mushrooms, but since a
mushroom is a rhizomorph composed of hypha fibers, the
pressure which water exerts when frozen was found to cause
a rhizomorph to be cracked up to destruction.
In view of the disadvantages of the various methods for
storage described above, the present inventor has made
extensive research for an effective method for storage capable
of preserving, with practically no loss in flavor or discolora-
tion, mushrooms such as Tricholoma Matsutake (ITO. et IMAI.)
SING. and Tricholoma ponderosum (PECK.) SI~NG. with which flavor
and appearance are important.
According to the present invention dried mushrooms are
prepared by vacuum drying.
According to one embodiment the inventive method is
characterized in that whole mushrooms or in slices 1-5 mm
thick are subject to vacuum drying. Preferably the vacuum
drying is continued to a water content of about 0.2% under
a high vacuum of about 10 mmHg.
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Conveniently the mushrooms are placed in a vacuum
drying vessel, the air inside which is then evacuated by a
vacuum pump via a cooling trap being cooled by a cooling
device.
The following is. a description by way of example of an
embodiment of the present invention reference being had to
the accompanylng drawings in which:
FIGURE 1 illus,trates an example of a vacuum drying
apparatus.
A suitab,le emb.odiment of the present invention will be
described in detail.
FIGURE 1 shows. a vacuum drying apparatus 10. A
vacuum drying vessel 12 is at room temperature. A cooling
trap 14 is connected to the vacuum drying ves.sel 12 via an
air suction tube 16. and also to a vacuum pump 20. via an
air suction tube 18. A cooling device 22 i.s. capable o~
cooling the inside of the cooling trap 14 down to 0.C. The
air suction tubes 16 and 18 are provided with valves. 24
and 26, respect~veIy.
20. A mushroom to be dried is placed in the. vacuum drying
vess-eI 12 and the vacuum pump 20 is put into operation to
evacuate the inside air from the vessel 12 via the suction
tube 16 7 cooling trap 14, and air suction tube. 18O The mush-
room will get rid of its water, gradually to dryness. The
water vapor coming from the mushroom is mostly condens.ed
in the cooling trap 14, partly taken out through the vacuum
pump 20.
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The condensation oE water vapor by the cooling trap 14
causes the pressure of inside water vapor to be lowered,
accelerating the vaporization or drying o~ the mushroom. In
an embodiment of the present invention, the air inside the
vacuum dry-ing vessel 12 may be evacuated directly by the
vacuum pump 20 with the cooling trap omitted. In such a
case, however, the drying speed is more or less lowered
and the vacuum pump 20 needs to be kept running. I~ the
vacuum pump 20 gets stopped when a high vacuum has been
reached inside the vacuum drying vessel 12, the ~ater vapor
pressure inside the vacuum drying vessel 12 is caused to
go up gradually until the vaporization of water ~rom the mush-
room is stopped. Thus, insu~ficient drying may occur and
the cessation of water vaporization will result in discolora-
tion and contraction of the mushroom.
With the cooling trap 14 provided, the mushroom may be
dried with increased speed as noted above, and also energy
saving may be effected by stopping the vacuum pump 20 when
the inside of the vacuum drying vessel 12 has reached a high
vacuum. This is because, even if the valve 26 is closed and
then the vacuum pump 20 is stopped when a high vacuum has
been reached inside the vacuum drying vessel 12, the water
vapor, which has~ been vaporized out into the vacuum drying
vessel 12, is allowed to condense in the cooling trap 14,
which condensation will induce further vaporization of water
from the mushroom.
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The vaporization of water deprives the mushroom of
the heat of vaporization~ This causes the mushroom to cool
down to about 0C, sometimes to a temperature as low as
-5C. By this- stage most water has been vapoxized out, with
the mushroom almost completely dried. Thus, water is not
caused to freeze so rapidly as to crack rhizomorphs, as
in the rapid freeze drying mentioned above, with a result
that the mushroom is favorably dried with its original shape
preserved. During the latter half of the drying process
by which time most ~ater has been vaporized out, the tempera-
ture of the mushroom will again go up. In the vacuum drying
where the temperature will change as described above, decomposi-
tion of flavor or taste components due to freezing will not
occur and, in contrast to drying by sunlight or fire, drying
proceeds under such a reduced oxygen pressure that any dis-
coloration due to oxidation does not occur.
Whole mushrooms may be dried sufficiently by ~acuum
drying.
With mushrooms; sliced to 1-5 mm in thickness, the drying
2a time may conveniently ~e shortened to a great extent since
the surface area has been increased with the travelling dis-
tance of water decreased.
The present invention is especially suitable for
Tricholoma ~atsutake (ITO. et IMAI.) SING, Trlcholoma pon-
derosum (PECK.) SING., Lentlnus edodes (BERK.) SING., and
.
LyophyLlum aggregatum (SCHAFF. et SACH.) K~HNER.
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Several embodiments of the present invention are given
below.
Example 1
Whole mushrooms were placed in a vacu~n drying vessel
at room temperature and the vessel was evacuated by a vacuum
pump and kep-t at a high vacuum 10 4 mmHg for 48 hours. The
mushrooms were ~ound dried to a water content of 0.2~, indi-
cating no state of having been frozen.
Example 2
At room temperature, mushrooms were sliced to 5 mm in
thickness and placed in a vacuum drying vessel. This vessel
was evacuated and kept at a high vacuum 10 4 mmHg for 36
hours. The sliced mushrooms were found dried to a water
content of 0,.2%, indicating no state of havin~ been frozen.
Example 3
At room temperature, mushrooms were sliced to 1-3 mm
in thickness and placed in a vacuum drying vessel. This
vessel was evacuated and kept at a high vacuum 10 4 mmHg for
24 hours. The sliced mushrooms were found dried to a water
content of 0.2%, indicating no state of having been frozen.
In the examples 1~3, the whiteness, of mushroom was
maintained, no di,scoloration being found at all. Almost
no indication was found of cracks in rhizomorphs, contraction,
or shape change. When the dried material was, recovered
by being ~i,ven water, and cooked, both its flavor and tooth
touch were found the same as before drying; the sweetness
was found rather increased by the drying.
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As described above, the present invention, which
provides vacuum drying, a drying method not severe for mush-
rooms, has a significant advantage that drying results in
virtually no loss of flavor~ increase in sweetness, no dis-
coloration, and neither cracks on rhizomorph nor contraction
which deforms the shape, and is especially suitable for
Tricholoma Matsutake (ITO. e-t I~AI.) SING. and Tricholoma
ponderosum (PECK.) SING. with which the appearance is important.
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The present invention has another significant advantage that
the dried product has such a high durability that fresh mush-
rooms may be supplied all the year round.
