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Corn
Make careful selection of tender juicy sweet corn, at the best stage for table use. Corn should be canned as soon as possible after gathering. Remove husks and silk; blanch tender ears 5 minutes, older ears 10 minutes. Cold dip and cut from cob. Do not cut too close to the cob. Pack at once into hot sterilized jars. As corn swells during sterilization, leave space of 1 inch at top. Add salt and cover with boiling water. Be sure that water penetrates through the corn to the bottom of the jar. Loosely seal and sterilize three hours in boiling water. Remove as soon as time is up, tighten covers, invert to test seal and cool. Label and store.
This is a boiling-water process for a low-acid vegetable, and that is the whole problem with it. The instructions are clear and were widely printed, but they do not produce a safe shelf-stable jar.
- Why the process failsSweet corn is a low-acid vegetable, well above the pH 4.6 threshold (published figures for corn generally fall somewhere in the 6-7 range), so Clostridium botulinum can grow in a sealed, oxygen-free jar. Boiling water tops out at 212F, and botulinum spores routinely survive hours at that temperature. Three hours in a water bath kills spoilage organisms that would have warned you and leaves the dangerous one alive.
- Density makes it worseCut corn packs tight and starchy, and heat moves through it slowly. The instruction to make sure water penetrates to the bottom of the jar is an acknowledgement of the problem, not a solution to it. The centre of the jar lags far behind the water bath even over three hours.
- Botulinum toxin gives no signAn affected jar of corn can look, smell and taste entirely normal. There is no visual test, no sniff test, and no rule about bulging lids that catches every case. This is why the hazard is treated differently from ordinary spoilage.
- Inverting is not a seal testTurning a hot jar upside down was standard practice for decades and is no longer recommended. It can pull food into the sealing surface and produce a weak seal that looks sound, and it tells you nothing about whether the contents were adequately processed.
- Salt "added" without measureThe recipe gives no quantity. Whatever the intention, salt at table-seasoning levels does not contribute to preservation; canning salt in vegetables is purely for taste.
- What to do insteadCorn can be canned safely, but only by a current tested process using a pressure canner, or else frozen. Use an up-to-date source such as the USDA or a national extension service rather than adapting the timings here.
Home canning guidance in the early twentieth century was in flux. Boiling-water and "intermittent" or fractional sterilisation methods, in which jars were boiled on successive days in the hope of catching spores as they germinated, filled the household manuals of the period, and instructions like these three hours in boiling water were printed in good faith. The push to preserve garden produce during and after the First World War put an enormous number of untrained cooks in front of a canner. Botulism was identified in the nineteenth century and its link to home-canned vegetables was becoming clear through the 1920s, but pressure canning at retort temperatures only became the standard domestic recommendation for low-acid foods over the following decades, as agricultural extension services worked out and published processing times for each vegetable and jar size. Pages like this one are a useful record of what careful householders were told before that work was done.