Abstract:
A system for preserving food, including a substantially anhydrous food mass, a substantially vitreous layer surrounding the substantially anhydrous food mass and defining an enclosure, and a partial vacuum formed within the enclosure. The substantially anhydrous food mass is typically a freeze-dried and compacted body, and the enclosure is typically defined by a contiguous glass shell, more typically a non-porous glass shell, enveloping the food mass.

Description:
TECHNICAL FIELD 
       [0001]    The novel technology relates generally to the field of food packaging, and, more particularly, to a method and system whereby food to be preserved is first freeze-dried and compressed, and then sealed in a low-oxygen environment in a glass container. 
       BACKGROUND 
       [0002]    Freeze drying or lyophilization is a well-known technique for preserving foods for storage at ambient temperatures for extended periods of time, provided the dried foods are maintained at very low moisture levels during storage. When properly prepared and stored, such freeze-dried foods may be rehydrated when desired for consumption. Depending on the freeze-drying technique employed and how well the foods were stored, the reconstituted foods may be of quality approximating that of freshly prepared foods, or may be of significantly lower quality (i.e., the reconstituted foods may be mushy, rubbery, or otherwise unappealing). 
         [0003]    In recent years, the armed forces have found compact freeze-dried foods desirable as meals ready to eat (MREs), as they are both space and weight efficient for storage on vehicles (particularly submarines and aircraft) and are easy for the average infantryman to carry. Further, compact and light freeze-dried foods are attractive for long term storage in emergency safety facilities and as emergency meals for sudden deployment to disaster victims. The freeze-drying process typically involves substantially removing the water from the food products by freezing them and then reducing the surrounding air pressure while adding sufficient heat to allow the frozen water to sublime directly from solid to gaseous phase. There are typically three stages in the freeze-drying process. First, the material to be dried is frozen to a temperature below that of the formation of water ice, and, more typically, to below the eutectic point of water (the lowest temperature where solid water ice and liquid water can coexist). This ensures that sublimation rather than melting will occur during the subsequent water removal steps. During the next phase the pressure is lowered and enough heat is supplied to the frozen food for the frozen water to sublimate. In this step, most of the water is removed via sublimation. Often, sublimation occurs under a partial vacuum to speed the drying process. Finally, a secondary drying step is often employed to remove adsorbed water accumulated during the preceding steps. In this phase, the temperature is raised even higher than in the primary drying phase to break any physico-chemical interactions that have formed between the water molecules and the frozen food. Typically, the pressure is also lowered in this stage to encourage sublimation, but the pressure may be elevated as well. After the freeze drying process is complete, the vacuum is usually broken with an inert gas, such as nitrogen, before the material is sealed. 
         [0004]    If a freeze-dried food is adequately sealed to prevent the reintroduction of moisture, the freeze-dried food may be stored indefinitely at room temperature without spoilage. Such storage is possible because the low moisture content inhibits the action of bacteria and enzymes that would otherwise act to spoil or degrade the substance. 
         [0005]    The freeze-drying process does not result in significant shrinkage of the freeze-dried foods. Thus, once freeze-dried, the food may be compressed or compacted for more efficient storage. One commonly employed method of compacting freeze-dried foods involves, after freeze-drying, spraying the food with sufficient water to raise its average moisture content to between about 5 and about 13% and then compressing the dried food. The moisture level is increased to make the food more plastic to allow the food to flow instead of shatter during compaction and to allow the food to retain its cellular structure. However, to assure adequate and homogeneous plasticization of the freeze-dried food, the dried food is sprayed with water (or, more typically, an aqueous solution of a gum or the like) and is then given sufficient time for the water to substantially equilibrate throughout the food. This process of homogenization may take hours or even days to complete. Further, after compaction, the added moisture must once again be removed via a dehydration step if the food is to benefit from the drying process enough to be stored at room temperature, again adding to the time and expense involved. 
         [0006]    It is desirable to be able to achieve the freeze-drying and compaction of the food mass without the lengthy rehydration process. However, if the food mass is only partially freeze-dried to an average moisture content of 5 to 13 percent, the moisture distribution is typically uneven, with the exterior of the food mass being almost completely dry and the core being still full of ice to almost it&#39;s normal moisture content. In one compaction method, the food mass is partially freeze-dried and then microwave heated to assist in melting the core to more rapidly remove the core water and achieve the level of hydration commensurate with the plasticity of the food mass for compaction. The food is then compacted and then dried sufficiently for storage. 
         [0007]    In another technique, the food mass is first partially dehydrated, and then freeze dried to moisture content level sufficient for plasticity. The food mass is then compacted, and then freeze-dried for storage. 
         [0008]    Once freeze-dried and compacted, the food may be stored for long, extended periods at room temperature. The storage time is limited by the how well the packaging of the food keeps out moisture. Most freeze-dried foods are sealed in plastic or metal containers, and may be so preserved for years or even decades. However, metal and plastic seals are still slightly porous and may degrade over time such that their porosity gradually increases, yielding an upper safe storage limit of about 25-30 years. While this is more than sufficient for most applications, food prepared and stored for use in rare and unusual emergency situations may be required to be stored for 50 to 60 years or even longer. Thus, there remains a need for an improved system for storing freeze-dried foods. The present novel technology addresses this need. 
       SUMMARY OF THE NOVEL TECHNOLOGY 
       [0009]    The present novel technology relates to a method and system whereby food to be preserved is first freeze-dried and then typically, but not necessarily, compressed, and then sealed in a low-oxygen/low-moisture environment in a glass container. One object of the present novel technology is to provide an improved food preservation system. Related objects and advantages of the present novel technology will be apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view of a method for freeze drying and compacting a food mass and then sealing the compacted and dried mass in a glass container according to a first embodiment of the present novel technology. 
           [0011]      FIG. 2  is a schematic view of a method for freeze drying and compacting a food mass and then sealing the compacted and dried mass in a glass container according to a second embodiment of the present novel technology. 
           [0012]      FIG. 3  is a schematic view of a method for freeze drying and compacting a food mass and then sealing the compacted and dried mass in a glass container according to a third embodiment of the present novel technology. 
           [0013]      FIG. 4  is a schematic view of a method for freeze drying and compacting a food mass and then sealing the compacted and dried mass in a glass container according to a fourth embodiment of the present novel technology. 
           [0014]      FIG. 5  is a schematic view of a user opening and eating the food mass stored according to one of the embodiments of  FIGS. 1-4 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    For the purposes of promoting an understanding of the principles of the novel technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel technology is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the novel technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the novel technology relates. 
         [0016]      FIGS. 1-4  illustrate a first embodiment of the present novel technology, a system  10  for preserving the integrity of dried goods, typically foods  12  that have been freeze-dried and, more typically, compacted for long term storage. The system  10  includes a dried and compacted food mass  14  that has been enveloped in a partial vacuum  16  formed inside a glass container  18 . More typically, the dried and compacted food mass  18  is wrapped in a protective sleeve  20 , such as a plastic film or the like, prior to positioning within the glass container  18 . The glass container  18  includes a central portion  22  and a lid portion  24  sealedly connected thereto to define a substantially contiguous vitreous or glassy enclosure  18 , such as via laser or torch fusion (wherein a laser, torch or like device is used to sufficiently heat the intersection of the lid and central portions  24 ,  22  such that they flow together to form, when cooled, a contiguous vitreous enclosure  18 ). (See  FIGS. 1 and 3 , respectively). Typically, water absorbing agents or desiccants  26  are placed in the enclosure  18  to further assure a substantially anhydrous environment therein. 
         [0017]    Alternately, the glass container  18  may include central and lid portions  22 ,  24  joined by a vitreous seal  28  formed from a sol-gel precursor; typically, the seal  28  is formed by layering multiple coatings of sol-gel precursor over each other while allowing sufficient time for the previous layer to substantially ‘dry’ or set up between applications. (See  FIG. 2 ). More typically, the central and lid portions  22 ,  24  each include a non-vitreous outer portion  30 ,  32  and a vitreous or glass inner layer liner portion  34 ,  36 . The sol-gel sealant  28  typically adheres to the outer portions  30 ,  32  at their intersection  38  and penetrates therebetween to also adhere to and form a glass seal between the inner liner portions  34 ,  36 . 
         [0018]    Still alternately, a glassy enclosure  18  may be formed around an intermediate container  40  enclosing the partial vacuum  16  and compacted, freeze-dried food mass  14 , such as by dipping the intermediate container in a glass source  42 , which may be a glass melt, a sol-gel precursor, or the like (see  FIG. 4 ). 
         [0019]    In operation, a long life freeze-dried food product  10  is generated by first preparing a compacted and freeze-dried food mass  50 ; the freeze-drying and compaction processes  52 ,  54  may be performed sequentially or simultaneously. Typically, the dried and compacted food mass  14  is then wrapped or enveloped  56  into a protective sleeve  20 , although this is not necessary and may be omitted. The wrapped (or unwrapped) food product  58  is enveloped  60  by a partial vacuum  16  and positioned in the enclosure  18 . The enclosure  18  is then sealed  62  to maintain the vacuum and desiccated environment therein. 
         [0020]    The glass enclosure  18  may be formed from the joining of glass central and lid portions of a glass container  18  (see  FIGS. 1 and 3 ), the joining of inner glass linings  32 ,  36  of the central and lid portions  30 ,  34  making up the container  18  (see  FIG. 2 ) or as a unitary coating formed over an inner vitreous or non-vitreous container (see  FIG. 4 ), such as by sol-gel or glass melt coating. 
         [0021]    When desired, the system  10  may be utilized by breaking  68  the glass seal  28  and/or enclosure  18 , removing  70  the compacted and dehydrated food mass  14  from the vacuum  16  and enclosure  18 , rehydrating  72  the compacted and dehydrated food mass  14 , and then eating  74  the rehydrated, reconstituted food (see  FIG. 5 ). 
         [0022]    While the novel technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the novel technology are desired to be protected.