152
_
FREEZE-DRYING
—
arefrozen'separately on special aluminium trays, because of disadvantageous interactions
between them, especially during‘t—hawing and-heating procedure.
*
4.272.- I—Iândling ànd prêtreaïment
'
'
'
‘
‘
,
…
'
’
Many foodstu‘s are quite susceptible to mechanical damaging whiCh can.happen during
rough handling of raw material; such injury may result not only in a higher microbial—
contamination of the produce but—especially. with fruits and vegetables—lead also to
some disorder in metabolism, which
produce e.g. o—avour. Therefore, an adequate
_
hygienic and careful handling of raw material previousto its freezing is often of great
importance for its quality and may even inuence its stability. '
'
As already mentioned, many enzÿmic reactions are not completely inhibited in the
mercially applied range of temperature for storage of frozen foods (+ 18 to —— 30 °C);
therefore in many cases, when active enzyme systems—are involved (e.g.
vegetables)
and the method is suitable, a blanching (orscalding) is applied; Because of undesirable
Changes caused by heat treatment in fruits, which are“ intended to be eaten raw, this method
is not always applicable; in such cases the undesirable changes may
be reduced by freezing
in sugar or sugar sirup..
_
ÎÉÏ
Most foods are frozen iii a retail package. Therefore, the choice of packaging material
Will inuence the stability of frozen products, too. Its low permeability to oxygen and
vapour may beof great importance because of oxydative »proceSses and loss of weight;
often it is also very desirable to have the wrapper very tightly surrounding the produce
,
(like poultry) so that freezer burn” could be prevented or at least be reduced.
'
_
4.2.3. Freezingmewd
_
;
’
The today—stage of development of freezing methods is very advanced; therefore the
freezing processes applied in a good commercial practice usually do not show any signicant
,
'
inuenCe on the stability of frozen foOds during storage. In very feWCasès a low rate of
;
freezing seems to shoVÿ'unsatisfactory results; but it is sure that in principle the inuence
“
of rate of freezing on the quality of frozen foods has been overestimated in the past, and
that it could be varied‘within quite a Wide range without asignicant effect On the most of
.,
,
frozen foods.
Today the choice of method of freezing is mostly inuenced—‘or even
dictated—by economical considerations and is often chosen according to the shape and
size Of the product —td
"
_
,
‘.
During the freezing ïprocess-Ÿthetemperature
the foOd”is‘ reduced to some average
value—equal to the equalization temperature—, which usually is at least —"— 18 °C and
,
corresponds totheint‘ended,_stoagetemperature or‘ to some predetermined‘temperature
'
,
'
l_(value) of the-thermàlcentre of the package
of
,1,.
at
‘_
,
,
,
theendofthefreezmgprocess hâ$‘fînb sighiCàt'iñiiëñôé0h the stability
’
stu”s becausemagoodcommermalpractme'itä1s”iïsi1ally deep *enôùgHad'iæcause the
«
The"mostimportantfactorsmuencmg thequahtyoffrozenfœdstusarethestorage
,
*
_
üeanäthestowgewnwüonsespec1allythereïaüvehum1dætyaudthetemperatuæand
_
FREEZE-DRYING
—
arefrozen'separately on special aluminium trays, because of disadvantageous interactions
between them, especially during‘t—hawing and-heating procedure.
*
4.272.- I—Iândling ànd prêtreaïment
'
'
'
‘
‘
,
…
'
’
Many foodstu‘s are quite susceptible to mechanical damaging whiCh can.happen during
rough handling of raw material; such injury may result not only in a higher microbial—
contamination of the produce but—especially. with fruits and vegetables—lead also to
some disorder in metabolism, which
produce e.g. o—avour. Therefore, an adequate
_
hygienic and careful handling of raw material previousto its freezing is often of great
importance for its quality and may even inuence its stability. '
'
As already mentioned, many enzÿmic reactions are not completely inhibited in the
mercially applied range of temperature for storage of frozen foods (+ 18 to —— 30 °C);
therefore in many cases, when active enzyme systems—are involved (e.g.
vegetables)
and the method is suitable, a blanching (orscalding) is applied; Because of undesirable
Changes caused by heat treatment in fruits, which are“ intended to be eaten raw, this method
is not always applicable; in such cases the undesirable changes may
be reduced by freezing
in sugar or sugar sirup..
_
ÎÉÏ
Most foods are frozen iii a retail package. Therefore, the choice of packaging material
Will inuence the stability of frozen products, too. Its low permeability to oxygen and
vapour may beof great importance because of oxydative »proceSses and loss of weight;
often it is also very desirable to have the wrapper very tightly surrounding the produce
,
(like poultry) so that freezer burn” could be prevented or at least be reduced.
'
_
4.2.3. Freezingmewd
_
;
’
The today—stage of development of freezing methods is very advanced; therefore the
freezing processes applied in a good commercial practice usually do not show any signicant
,
'
inuenCe on the stability of frozen foOds during storage. In very feWCasès a low rate of
;
freezing seems to shoVÿ'unsatisfactory results; but it is sure that in principle the inuence
“
of rate of freezing on the quality of frozen foods has been overestimated in the past, and
that it could be varied‘within quite a Wide range without asignicant effect On the most of
.,
,
frozen foods.
Today the choice of method of freezing is mostly inuenced—‘or even
dictated—by economical considerations and is often chosen according to the shape and
size Of the product —td
"
_
,
‘.
During the freezing ïprocess-Ÿthetemperature
the foOd”is‘ reduced to some average
value—equal to the equalization temperature—, which usually is at least —"— 18 °C and
,
corresponds totheint‘ended,_stoagetemperature or‘ to some predetermined‘temperature
'
,
'
l_(value) of the-thermàlcentre of the package
of
,1,.
at
‘_
,
,
,
theendofthefreezmgprocess hâ$‘fînb sighiCàt'iñiiëñôé0h the stability
’
stu”s becausemagoodcommermalpractme'itä1s”iïsi1ally deep *enôùgHad'iæcause the
«
The"mostimportantfactorsmuencmg thequahtyoffrozenfœdstusarethestorage
,
*
_
üeanäthestowgewnwüonsespec1allythereïaüvehum1dætyaudthetemperatuæand