GB2209114A - Dehydration of foodstuffs - Google Patents
Dehydration of foodstuffs Download PDFInfo
- Publication number
- GB2209114A GB2209114A GB8718834A GB8718834A GB2209114A GB 2209114 A GB2209114 A GB 2209114A GB 8718834 A GB8718834 A GB 8718834A GB 8718834 A GB8718834 A GB 8718834A GB 2209114 A GB2209114 A GB 2209114A
- Authority
- GB
- United Kingdom
- Prior art keywords
- ice
- foodstuff
- water
- vacuum
- microwave
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/40—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by drying or kilning; Subsequent reconstitution
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B4/00—General methods for preserving meat, sausages, fish or fish products
- A23B4/03—Drying; Subsequent reconstitution
- A23B4/037—Freeze-drying, i.e. cryodessication, lyophilisation; Apparatus therefor
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/02—Dehydrating; Subsequent reconstitution
- A23B7/024—Freeze-drying, i.e. cryodessication or lyophilisation
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Food Science & Technology (AREA)
- Polymers & Plastics (AREA)
- Wood Science & Technology (AREA)
- Zoology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Nutrition Science (AREA)
- Freezing, Cooling And Drying Of Foods (AREA)
Abstract
A method of dehydrating water-containing foodstuffs including fruit, vegetables, meat, fish and the like, comprising the steps of (a) partially freezing the foodstuff until a proportion of the water included therein has frozen to produce ice in sufficient quantity to create a rigid structure in the foodstuff and (b) applying a microwave drying technique under a selected degree of vacuum to remove the ice by sublimation and the unfrozen water by evaporation.
Description
Title: Dehydration of foodstuffs
The invention is concerned with improvements in or relating to the dehydration of foodstuffs including fruit, vegetables and the like, for the purposes of preserving the same from deterioration.
It is known that the storage life of foodstuffs is greatly increased if they are dried to a low moisture content.
However, conventional and traditional methods of drying result in a loss of texture and the product is not easily rehydrated to an acceptable standard.
It is an object of the invention to disclose a method of drying wet materials and, in particular but not exclusively, foodstuffs such as fruit, vegetables, meat and fish, in which the water is evaporated at low temperature with the cellular structure of the material being retained in such a way as to form a rigid porous sponge which is capable of rapid rehydration.
The invention provides a method of dehydrating water containing foodstuffs including fruit, vegetables, meat, fish and the like, comprising the steps of (a) partially freezing the foodstuff until a proportion of the water included therein has frozen to produce ice in sufficient quantity to create a rigid structure in the foodstuff and (b) applying a microwave drying technique under a selected degree of vacuum to remove the ice by sublimation and the unfrozen water by evaporation.
In an example of the invention, the method comprises the following steps: (i) Freezing the product partially so that a mixture of
ice and liquid exists such that sufficient ice is
formed to create said rigid structure to the product.
The proportion of ice for optimum results will vary
for different products but generally will be in the
range 5% to 30% ice. However this range is given for
illustration only and a lesser or higher proportion
of ice is within the scope of the invention.
(ii) Using microwave vacuum drying to evaporate the liquid
in the partially frozen product, and to evaporate the
ice by sublimation.
It will be appreciated that the liquid will freeze in the same manner as a brine solution, that is that the ice formed will be of pure water whilst the concentration of the dissolved salts will rise in the remaining liquor as more ice forms. Ultimately all the liquid would freeze at the freezing point of the saturated solution, but it is not intended in this method to freeze the product to this low o Q temperature which would generally between -10 C and 40 C.
It will also be appreciated that from the partially frozen state, the ice will not melt until the temperature rises to
o
O C and the appropriate latent heat is injected unless the pressure is below the critical value at which ice sublimes.
The vacuum pressure may be set to a level at which the
o liquid solution boils at less than 0 C. For example the
o concentrated solution may freeze at -25 C, but its boiling
o point, which is a function of pressure, may be set to -5 C by choice of suitable vacuum pressure. By this means the boiling point of residual liquor after partial freezing as in step (i) may be at a lower temperature than the melting point of the ice.
The residual liquor can therefore be evaporated without melting the ice, simultaneously ice in close thermal contact with the liquor will sublime.
It will be appreciated that the partial freezing only of the product is very advantageous for the subsequent microwave drying because the microwave loss factor of the liquor is high, so that the electric field intensity required to give a satisfactory power dissipation density is low, within practical limits. Typically the dielectric properties at the start of drying would be e' = 5, e" = 0.8. At 2450 MHz with a field intensity external to the product of 100 V/cm the power density would be 0.7 watts/cc, giving a drying time in the order 50 minutes in a product with 15% solids.
The voltage stress applicable is a function of vacuum pressure and can be raised to give more rapid drying by
-l reducing the pressure to less than 10 torr. However, the rate of drying is limited also by the diffusion rate of steam through the product, which must not create such a pressure gradient within it that the internal pressure exceeds the critical value at which ice melts instead of sublimes in the central region.
In summary, the salient features of the example may be expressed as follows: (a) The partial freezing of the material to form at least
sufficient ice to create a rigid structure with a
residual liquid content to provide a microwave loss
factor e" of at least 0.2.
(b) Reduction of pressure to a level less than that at
which ice sublimes, or to lower the boiling point of
o
the residual liqor below 0 C whichever is the lower.
(c) The application of heat energy at least in part as
microwave energy to evaporate the residual liquid and
sublime the ice so as to reduce the moisture content
to the required final value. Some of this energy may
be of heat-conduction or infra-red radiation source.
It is to be noted that the present invention provides an improvement over the usual freeze-drying technique for three important reasons: (1) The residual liquor from partial frezing provides a
microwave loss factor making microwave energy a
practical heat source.
(2) Energy is saved in avoiding (a) total freezing and (b)
requiring less energy for drying.
(3) The use of microwave energy speeds up the whole
process with the usual consequent advantages.
Various modifications may be made within the scope of the invention.
Claims (8)
1. A method of dehydrating water-containing foodstuffs comprising the steps of (a) partially freezing the foodstuff until a proportion of the water included therein has frozen to produce ice in sufficient quantity to create a rigid structure in the foodstuff and (b) applying a microwave drying technique under a selected degree of vacuum to remove the ice by sublimation and the unfrozen water by evaporation.
2. A method as claimed in claim 1 wherein the partially frozen foodstuff contains 5-30% ice
3. A method as claimed in claim 1 or 2, wherein the degree of vacuum is selected such that any unfrozen liquid in the foodstuff boils at -50C.
4. A method as claimed in any preceding claim, wherein the microwave frequency is 2450 MHz and the field intensity external to the product is 100 V/cm.
5. A method as claimed in any preceding claim, wherein the vacuum pressure is 10 1 torr.
6. A method as claimed in any preceding claim, wherein the partial freezing is sufficient to provide a microwave loss factor e" of at least 0.2.
7. A method as claimed in any preceding claim, wherein heat is also provided by heat conduction or infra red radiation.
8. A method which is substantially as herein described.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8718834A GB2209114A (en) | 1987-08-08 | 1987-08-08 | Dehydration of foodstuffs |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8718834A GB2209114A (en) | 1987-08-08 | 1987-08-08 | Dehydration of foodstuffs |
Publications (2)
Publication Number | Publication Date |
---|---|
GB8718834D0 GB8718834D0 (en) | 1987-09-16 |
GB2209114A true GB2209114A (en) | 1989-05-04 |
Family
ID=10622025
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB8718834A Withdrawn GB2209114A (en) | 1987-08-08 | 1987-08-08 | Dehydration of foodstuffs |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2209114A (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2235755A (en) * | 1989-08-09 | 1991-03-13 | Elemer Varga | Preparing fruit powder |
US5484606A (en) * | 1994-01-24 | 1996-01-16 | The Procter & Gamble Company | Process for reducing the precipitation of difficulty soluble pharmaceutical actives |
CN103948151A (en) * | 2014-04-19 | 2014-07-30 | 宁国中科生物科技有限公司 | Fruit and vegetable microwave drying system |
CN109393004A (en) * | 2018-09-28 | 2019-03-01 | 上海锦立保鲜科技有限公司 | A method of vacuum thawing is realized using the free water sublimate of frozen product |
US11547131B2 (en) | 2015-10-14 | 2023-01-10 | Enwave Corporation | Method of making dried food products |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN115104694B (en) * | 2022-07-13 | 2024-02-27 | 青岛鑫复盛食品科技有限公司 | Food thawing apparatus |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB871248A (en) * | 1956-10-11 | 1961-06-21 | Raytheon Co | Improvements in or relating to methods and apparatus for removing a relatively volatile component from frozen material |
GB1074062A (en) * | 1964-03-25 | 1967-06-28 | H J Heinz Company Ltd | Improvements in or relating to method of de-hydrating materials |
GB1343640A (en) * | 1970-02-27 | 1974-01-16 | Inst Rech Appliquees Aux Boiss | Process for the preparation of a vegetable powder instantly soluble or microdispersible in water |
US4096283A (en) * | 1976-11-08 | 1978-06-20 | The United States Of America As Represented By The Secretary Of The Army | Method of compacting freeze-dried particulate foods |
GB2070217A (en) * | 1980-02-05 | 1981-09-03 | House Food Industrial Co | Method for producing dry fruit chips |
-
1987
- 1987-08-08 GB GB8718834A patent/GB2209114A/en not_active Withdrawn
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB871248A (en) * | 1956-10-11 | 1961-06-21 | Raytheon Co | Improvements in or relating to methods and apparatus for removing a relatively volatile component from frozen material |
GB1074062A (en) * | 1964-03-25 | 1967-06-28 | H J Heinz Company Ltd | Improvements in or relating to method of de-hydrating materials |
GB1343640A (en) * | 1970-02-27 | 1974-01-16 | Inst Rech Appliquees Aux Boiss | Process for the preparation of a vegetable powder instantly soluble or microdispersible in water |
US4096283A (en) * | 1976-11-08 | 1978-06-20 | The United States Of America As Represented By The Secretary Of The Army | Method of compacting freeze-dried particulate foods |
GB2070217A (en) * | 1980-02-05 | 1981-09-03 | House Food Industrial Co | Method for producing dry fruit chips |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2235755A (en) * | 1989-08-09 | 1991-03-13 | Elemer Varga | Preparing fruit powder |
US5484606A (en) * | 1994-01-24 | 1996-01-16 | The Procter & Gamble Company | Process for reducing the precipitation of difficulty soluble pharmaceutical actives |
CN103948151A (en) * | 2014-04-19 | 2014-07-30 | 宁国中科生物科技有限公司 | Fruit and vegetable microwave drying system |
US11547131B2 (en) | 2015-10-14 | 2023-01-10 | Enwave Corporation | Method of making dried food products |
CN109393004A (en) * | 2018-09-28 | 2019-03-01 | 上海锦立保鲜科技有限公司 | A method of vacuum thawing is realized using the free water sublimate of frozen product |
Also Published As
Publication number | Publication date |
---|---|
GB8718834D0 (en) | 1987-09-16 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |