a description of preferred embodiments of the invention follows . one embodiment of the invention is illustrated in fig1 - 3 . in step 10 , a commodity is hermetically sealed in a flexible container or enclosure 18 , such as that formed from a 0 . 813 mm ( 0 . 032 inch ), low air - permeable , ultraviolet - resistant food grade polyvinyl chloride sheet ( pvc ) material . in one embodiment , the container can include a pvc enclosure marketed by grainpro , inc . of concord , mass . under the trade name cocoons ™. the commodity can be packaged in individual jute bags 22 and stored on pallets 24 within the enclosure 18 . in the context of a hermetic enclosure , low air - permeable can be defined as low air - permeability through the enclosure compared to the initial consumption of air by the insects . if a vacuum is used , low air - permeable can be defined as low air permeability through the enclosure compared to the pumping capability of the vacuum at a designated pressure . in one embodiment , the enclosure is 15 m 3 with a ten metric ton capacity , and has an infiltration rate of less than about 10 liters / minute at 40 mm hg . even lower infiltration rates can be achieved with different materials that form the low air - permeable enclosures . in step 12 , a vacuum 20 is established in the enclosure by using a conventional commercial vacuum pump and set point regulator . the flexible container or enclosure prevents excessive stresses when evacuated as would occur with a rigid container by conforming to the shape of the enclosed commodity . the vacuum 20 , as shown in fig3 can include a vacuum pump 26 driven by a motor 28 . tubing or hose 38 connects the enclosure 18 to the vacuum pump 26 . an opening in the enclosure 18 , which can be opened or closed by means such as a solenoid - controlled inlet valve , is fed to the vacuum pump 26 with , if needed , an appropriate filter 30 in line 38 to prevent clogging or damage to the pump . in a particular embodiment , the vacuum pump 26 is allowed to run for an extended period of time so that either or both oxygen and interstitial moisture inside are substantially removed , typically down to a vacuum of 25 - 100 mm hg at room temperature representing an oxygen level equivalent to normal pressure of 3 - 13 %. at this time , the inlet valve is closed , and the hermetically sealed enclosure becomes a large “ vacuum pack ” ( step 14 ), with periodic pumping as required to compensate for residual infiltration of air , eliminating any of the respective causes of degradation named above due to either direct or indirect effects of oxygen . further , any residual moisture in the absence of oxygen will not as easily cause moisture - produced damage . the vacuum 20 can be controlled by control panel 34 coupled to a pressure sensor 32 to maintain a desired vacuum level . in alternative embodiments , the vacuum pump 26 runs continuously during storage of the commodity and is turned on and off by an on / off switch . the time , temperature , and vacuum conditions for removing biologically - active contaminants are a function of the type of contaminant , e . g ., the type of insect infestation , temperature , and the desired kill time . for example , it has been found that a 100 % kill of insects in coffee and cocoa beans can be achieved in three days using a vacuum in the range of 30 - 50 mm hg at room temperature . in some applications , it is desirable to remove the oxygen from the stored commodity to preserve the freshness which affects the taste of the commodity . in other applications , it is desirable to remove the oxygen from the stored commodity so that growth of fungi is curtailed and hence the production of aflatoxins . thus , in step 16 , the temperature of the commodity is maintained sufficiently high to ensure substantial kill of infesting insects within a desired time period . generally , the higher the temperature , the faster the insects will die as they respire more rapidly to deplete air within the hermetic enclosure 18 . in alternative embodiments , an insecticidal gas , such as propylene oxide , ozone , etc ., can be injected into the hermetic enclosure 18 , before or after applying a vacuum to the enclosure , to accelerate the kill time of the insects . in a particular embodiment , the insecticidal gas is injected into the hermetic enclosure prior to applying a vacuum to the enclosure 18 . of course , when additional gases are injected into the hermetic enclosure 18 , care must be taken to avoid gas mixtures which are flammable , explosive , etc . removal of the commodity from the sealed enclosure can be made through a commercially available hermetic “ zipper ,” such as the zipper sold by itw maxigrip specialty applications group under the trademark maxigrip , that is provided on the hermetic enclosure . it has been shown experimentally that the kill time for various life stages and species of insects varies as between life stages and species and is a strong function of ambient temperature . as shown in the table below , for 3 common insect pests , the kill time varies between the insects , and between the different life stages of the same insect . in these experiments , a commodity was placed in a hermetic enclosure 18 and a vacuum of 35 mm hg was applied . life insect species stage 25 ° c . 33 ° c . 37 ° c . 40 ° c . tribolium eggs 27 . 62 hours 16 . 31 hours 11 . 17 hours 4 . 12 hours castaneum ( red flour larvae 3 . 46 hours 3 . 29 hours 2 . 56 hours 1 . 94 hours beetle ) pupae 12 . 73 hours 11 . 48 hours 9 . 35 hours 3 . 83 hours plodia eggs 28 . 35 hours 6 . 21 hours 4 . 00 hours 2 . 49 hours interpunctella ( indian meal larvae 3 . 99 hours 2 . 69 hours 2 . 07 hours 2 . 10 hours moth ) pupae 5 . 35 hours 2 . 65 hours 2 . 44 hours 1 . 64 hours rhyzopertha eggs 176 . 32 hours 85 . 98 hours 46 . 32 hours 11 . 24 hours dominica ( lesser grain larvae 83 . 80 hours 49 . 58 hours 19 . 45 hours 6 . 47 hours borer ) pupae 98 . 28 hours 56 . 20 hours 22 . 14 hours 8 . 65 hours it has been discovered that the minimum temperature needed to ensure substantial total kill of all infesting insects within a desired time period is reached at substantially all portions of the commodity . thus , one must maintain the coolest part of the commodity at or above a given temperature , for example , with a heated warehouse , in the hermetic enclosure 18 for the greatest time period of the 3 life stages to kill the desired species . it has been found that a vacuum of between about 35 - 50 mm hg and a temperature above about 18 degrees celsius , and particular in the range of about 25 - 40 degrees celsius , works particularly well in the storage of some commodities . while this invention has been particularly shown and described with references to preferred embodiments thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims .
a method and system for storing of a bulk commodity utilizes a flexible , low air - permeable sheet material enclosure in which the bulk commodity is hermetically sealed . the atmosphere in the sealed flexible sheet material enclosure is evacuated to establish a vacuum therein . the vacuum is maintained during at least a portion of the storage of the commodity to ensure a significant reduction of the commodity . the temperature of the commodity is maintained sufficiently high to ensure substantial total kill of infesting insects within a desired time period . at least a portion of the commodity can be removed from the enclosure by opening a hermetic seal therein .