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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Canning Vegetables
In canning vegetables the same precautions must be observed as in canning fruit and it is safer to use jars that have either glass tops, or tops without porcelain lining. Corn should be pressed or cut from the cob and packed at once into jars, and, in order to insure its keeping, the cold-pack method should be followed. See directions on page 318.
Peas may be packed in the same way as corn, but each jar must be filled with water; string beans require a shorter period of cooking, but the jar manipulation is the same. See time-table, page 323. Add a teaspoon of salt to each jar of vegetables.
This page is a set of instructions for putting up food, so it counts as a recipe — but it is one that current science has ruled out entirely. The points below explain what specifically fails.
- Corn, peas and beans are low-acidAll three sit around pH 6, well above the 4.6 threshold below which Clostridium botulinum cannot grow. Nothing in this method acidifies them, so the jars provide exactly the oxygen-free, low-acid, room-temperature environment the organism needs.
- Boiling water cannot kill the sporesBoiling water cannot be relied on to kill the spores -- The "cold-pack" method referenced here processes jars in boiling water, which tops out at 212F. Botulinum spores can survive hours at that temperature; reliably destroying them in low-acid food requires around 240F, which only a pressure canner reaches.
- Corn and peas are the worst caseStarchy vegetables pack densely and conduct heat poorly, so the centre of the jar lags far behind the water bath. Even a long boiling-water process leaves a cool core. Home-canned vegetables of this kind, corn and beans among them, are regularly implicated in botulism cases.
- The salt does nothing protectiveA teaspoon per jar is a seasoning level, perhaps one percent of the contents. Inhibiting bacterial growth by salt alone takes brine strengths many times that, at which point the vegetables are salt-preserved, not canned.
- No temperature, no pressure, no verified timesThe instructions point to a time-table on another page and otherwise give no processing pressure or internal temperature. There is no way to confirm a lethal process was achieved, and spoiled low-acid jars frequently look, smell and sound perfectly normal.
- The jar advice is obsolete on its own termsGlass-topped jars and zinc caps with porcelain liners were the closures of the day; the two-piece lid with a single-use sealing compound that modern guidelines assume was not yet in general use. Vintage closures cannot be relied on to hold a vacuum.
- If you want to put up vegetablesUse a current pressure-canning guide from the USDA or a university extension service, which specifies pressure, time and jar size for each vegetable. Freezing is the simpler route for corn, peas and beans.
Loose-leaf cookbooks like Mrs. Fryer's were sold in the 1910s and 1920s as expandable household manuals, and their canning sections rode a wave of official enthusiasm: wartime food-conservation campaigns pushed home canning hard, and the "cold-pack" or one-period boiling-water method was promoted widely by clubs and demonstration agents because it needed no special equipment. The trouble was that the science had not caught up. Botulism had been described in the nineteenth century from spoiled sausage and ham — the name comes from Latin botulus, sausage — but its link to home-canned low-acid vegetables was only being pinned down in American laboratories in the late 1910s and 1920s, and the pressure canner did not become standard household advice until the following decades. Pages like this one are a snapshot of the interval between the advice and the evidence, which is precisely why it is worth reading and not worth following.