Important: Safety Warning
This page describes home-canning methods from before the causes of botulism were understood. Canning low-acid foods without a pressure canner, as described here, can allow the growth of Clostridium botulinum, whose toxin is among the deadliest known. Follow current USDA home-canning guidelines instead.
This information has been left in for historical purposes but should not be acted upon.
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How to Can Green Corn (No. 2)
Cut ripe sweet corn from the cobs and pack in glass jars, pressing the corn down as tightly as possible. A little wooden mallet that exactly fits the jar is useful to press it down with. To each quart can, add 1 teaspoon salt. Place the cans in a wash boiler, on the bottom of which has been placed a thick folded cotton cloth. Have the covers of the cans screwed down very tightly. Fill the wash boiler to the neck of the cans with cold water, cover and let boil for 3 hours and a half. Take cans out and screw down airtight. When cool, set in the cellar and you have lovely sweet corn all winter for all purposes. I have tested this several times and never had one can spoil yet. -Mrs. H. J. B., Craighurst, Ont.
This is a boiling-water-bath method applied to a low-acid vegetable, and it is one of the clearest examples in the book of a technique that later science ruled out entirely.
- Why corn specifically failsSweet corn has a pH around 6.0 to 6.8, far above the 4.6 threshold below which Clostridium botulinum spores cannot grow. Water in an open wash boiler cannot exceed 212F, and botulinum spores are so heat-resistant at that temperature that boiling will not destroy them in any practical length of time; only the 240F reached under pressure destroys them reliably.
- The packing makes it worsePressing the kernels down with a mallet until the jar is solid creates a dense mass that heat penetrates very slowly. Modern pressure-canning instructions for corn call for a loose pack precisely because a tight one leaves a cold centre.
- Three and a half hours is not a substituteLong boiling is a reasonable instinct but the wrong variable. Time at 212F does not compensate for insufficient temperature against heat-resistant spores; the jars simply spend longer in the range where surviving spores will later germinate.
- The salt does nothing hereOne teaspoon per quart is for flavour. Salt inhibits botulinum only at brine concentrations far higher than this, of the kind used in salt-cured pork.
- Lids screwed tight before processingSealing hard before heating traps expanding air and can force the seal or crack the jar. Contemporary practice is a fingertip-tight band so air can vent, with the vacuum forming as the jar cools.
- "Never had one can spoil yet"Botulinum toxin usually produces no bulging, no off smell and no cloudiness. A jar that looks and smells perfect can be lethal, which is exactly why this method persisted in print for decades after it should have been abandoned.
- If you want canned cornUse a current USDA or provincial extension recipe written for a dial-gauge or weighted-gauge pressure canner, with the processing time adjusted for your altitude. Freezing blanched kernels is the simpler route for a home cook.
Home canning of low-acid vegetables in a wash boiler was ordinary practice across rural Canada and the United States when the Five Roses Cook Book was assembled from readers' contributions in 1913 — the credit line to Mrs. H. J. B. of Craighurst, Ontario is typical of the book, which was built largely from letters sent in by women who used Lake of the Woods Milling Company flour. Botulism had been described in Europe in the nineteenth century in connection with spoiled sausage, which is where the name comes from (botulus, Latin for sausage), but the link between the organism and improperly canned vegetables was only worked out in North America in the 1910s and 1920s, after a run of fatal outbreaks traced to commercially and domestically canned goods. Pressure canners existed in this period but were expensive and uncommon in farm kitchens; the wash boiler and a folded cloth on the bottom were, by most accounts, what a great many households were likely to have had. The confident closing line — several seasons, not one can spoiled — is the honest testimony of someone who had been lucky, and it is a good illustration of why food safety came to rest on measured temperatures rather than accumulated household experience.