In Japan, you can find full (unsheathed) corn on the cob that’s been vacuum packed, sold as individual units. They last about 6 months, and in my experience taste just fine.
I have noted, though, that when I open the pack, there’s a small amount of liquid in there with the corn. I’m not sure if this is salt water or sugar water to preserve it, or if they boiled/washed the corn first and didn’t dry it properly before sticking it in.
Overall, I’m just wondering how one would preserve a corn himself, like this?
According to this page (scroll down to the part titled 真空パック詰めのボイルコーンを販売) it’s boiled immediately before being packed. Would that be enough to make it shelf stable? The first page I linked to stated that there are no additives.
This is a decent picture of the corn, for those who haven’t seen it before.
Vacuum sealing alone will not make it shelf stable, even if it is boiled immediately before packaging, because the corn and the packaging are exposed to bacteria-laden air after boiling. Food canned in tins, jars and retort pouches are all essentially cooked in the package, then sealed in such a way that air cannot re-enter the package.
Unless that corn is cooked in a retort while in the package, it is not intended to be shelf stable. Refrigerate, or consume at your own risk beyond a day or two.
Food that is properly cooked in a pouch (i.e so internally or externally generated steam displaces air before sealing) will become vacuum-packed when the bag cools. The internal pressure will only be the vapor pressure of water at that temperature. This is, in fact how both home and factory canning “work”. This would also leave trace free water.
However exposure to outside air (much to my surprise) turns out not to be the stamp of doom that I would have believed. For example, Campbell’s Soup (chosen only because it was the example that I saw packaged) only heats the cans to 180-190F (not a full boil) for 20 minutes on a water table, after the cans are filled. I’m afraid I don’t recall if the cans were lidded but not sealed (which makes more sense to me, or sealed (as I vaguely recall hearing) during this stage. I [refer to believe it is lidded but not sealed, ewhich makes more sense, and is also the process used in home canning (whether the lid consists of a flat sealing plate and a threaded sealing ring to clamp it tight once the contents have been heated tothe target temperature for the desired time.
Bacterial or other spoilage, whether aerobic or anaerobic, usually generates gases, which visibly ruin the bag’s “vacuum” – sooner than a metal soup can would bulge.
I found a Japanese patent application from 2000 for vacuum sealing corn here. It’s getting late so I only skimmed it, but while the application states that it is a replacement for retort pouching it appears to be a similar process in which the corn is sealed first and then heat treated.
