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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Preserving and Canning Fruit and Vegetables: Select
Select preferably the sweetest and most delicate varieties. Experiment has proved that the amount of sugar in sweet corn diminishes very rapidly after the ear is pulled from the stalk. Hence endeavor to get the kernels into the can within an hour after the corn is picked. If this can be done the result will be far superior to the ordinary commercial product. Select ears with full grains, just before they begin to harden, since the corn is then sweetest. Husk the ears and remove the silks with a stiff brush. Sheer off the grain with a sharp knife, pack the jar full and salt to taste, usually at the rate of one teaspoonful to the quart.
Fill up the jar to the top with clear cold water, put on the rubber ring and place the glass top on loosely but without depressing the spring.
Now place the jars upon a false bottom in a wash boiler and separate Sterilizer, showing false bottom. (J. F. Breazeale.) them by means of rags or cotton rope, such as an old clothesline, so that they cannot strike one another when the water begins to boil. Pour in about three inches of cold water or enough to fill the boiler with steam. More than enough to prevent the boiler from going dry is not necessary as the steam will do the cooking. Cover the boiler tightly, bring to a boil and let boil for a full hour. Now remove the cover and allow the steam to escape. Press down the spring to prevent air from entering. Remove the jars to cool, or let them stand in the boiler until the next day.
On the second day raise the spring as before and again boil for one hour. Once more clamp down the top and let stand until the following day. Then repeat the operation. Observe that the jars when hot must be carefully shielded from drafts of cold air or the sudden change of temperature will crack them.
After the third boiling clamp on the top and let stand two or three days. Then test each jar by releasing the spring and picking up the jar by the glass top. If the top does not come off the contents are reasonably sure to keep unless there should chance to be one or more anaerobic bacteria present which may cause trouble later on. Should this happen increase the length of boiling for the next lot to 1½ hours. If the tops come off when the can is tested, decomposition has begun to take place and gases have been formed which offset the atmospheric pressure on the outside of the jar.
In this case it is best to reject the contents and to cleanse and refill the jar.
The above directions apply only to pint and quart jars. Increase the time of boiling for half gallon jars to one and a half hours. A little practice may be required at first to secure perfect results by this method; hence do not try too many jars the first time. Make a few experiments in the early part of the season until you fully understand the directions and learn to follow them properly. After that there will be no difficulty and the benefits of fresh vegetables from the kitchen garden will be extended to every season of the year.
The same general process applies to canning other vegetables except for the mode of preparing them, as to which the following suggestions are offered:
This is the classic "intermittent" or "fractional" boiling-water method for canning sweet corn, and it is the single most dangerous procedure in the old preserving literature. The notes below explain why it fails rather than how to adapt it.
- Why corn is the worst caseSweet corn is very low in acid, around pH 6 and so well above the 4.6 line that divides acid from low-acid foods, and it is dense and starchy so heat penetrates the packed jar slowly. Those are precisely the conditions under which Clostridium botulinum spores survive and then germinate in the oxygen-free jar.
- 212F is not hot enoughBoiling water and atmospheric steam both cap out at about 212F. Botulinum spores need roughly 240F, which only a pressure canner reaches. Three hours of boiling spread over three days does not add up to one sterilizing treatment; the spores simply are not killed at any point.
- The three-day rest is the flaw, not the safeguardThe original logic was that surviving spores would sprout into vulnerable vegetative cells overnight and be killed by the next boil. Some do, but in a sealed low-acid jar the germinating cells are also producing toxin, and any toxin formed after the final boil stays in the jar. The rest periods are an incubation.
- The spring-top test proves nothingA jar that holds its seal has only demonstrated that no gas-forming spoilage organism grew. Botulinum in corn may produce no bulging, no off smell and no cloudiness. A jar that looks and smells perfect can be lethal.
- The author's own caveatThe line about "one or more anaerobic bacteria present which may cause trouble later on" is the whole hazard, stated and then dismissed. The remedy offered, adding half an hour to the boil, does not raise the temperature and so does not change the outcome.
- Do not scale or salvage itThere is no correction to this method: not longer boiling, not more salt, not more days. Salt at a teaspoon to the quart is for flavour and has no preservative effect at that level. If you want home-canned corn, use a current USDA-tested pressure-canning procedure from a present-day source.
- The one part still worth keepingThe observation about sugar loss is sound. Sweet corn does convert sugar to starch quickly after picking, which is why an hour from stalk to kitchen still makes a real difference, whether you are freezing it or eating it the same night.
This passage sits in the era between Pasteur and the modern canning bulletin, when home preserving was being actively promoted as a scientific household art but the mechanism of botulism was not yet understood in American kitchens. The illustration credit to J. F. Breazeale points to the kind of government and agricultural-station chemist whose work fed into popular household compendiums of the period; the makeshift sterilizer, a wash boiler with a false bottom and jars separated by lengths of old clothesline, is exactly what an ordinary kitchen had to work with before domestic pressure canners were widely sold. The intermittent or fractional method described here descends from Tyndall's nineteenth-century sterilization experiments and was recommended in good faith for decades. Botulinum was identified in the 1890s from spoiled preserved meat in Europe, but the link to home-canned low-acid vegetables was only pinned down in the United States in the years around and after the First World War, and pressure-canner processing times for vegetables were not standardized for home use until later still. Pages like this one are the reason those standards exist.