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
1. Make a false bottom to fit inside an ordinary wash-boiler. This bottom may be a piece of heavy wire netting or a wooden grating. 2. Prepare the vegetables as for cooking and in convenient form for placing in the cans. Root vegetables should be brushed clean, peeled and cut into convenient slices or pieces. Green beans should have their strings removed and then be cut into short lengths. Peas should be shelled. Corn should be cut off the cob. Squash should be peeled.
Peppers should be scalded and the skins and seeds removed, and the flesh cut up into small pieces. Asparagus should be blanched or parboiled by dipping into boiling water for about three minutes immediately before canning. Artichokes should have some of the outside bracts removed and the hard tip cut off with a sharp knife. 3. The prepared vegetables are packed tight into the jars or cans which are then completely filled with brine containing three ounces of salt to a gallon of water. Before using, this brine should be acidified with lemon juice or vinegar.
For corn ten fluid ounces (about one and one-half teacups) of lemon juice should be used to a gallon of brine, for beans and peas seven fluid ounces (about one teacup), and for other vegetables five fluid ounces (about three-fourths of a teacup). If ordinary vinegar is used, about twice these quantities are necessary.
The acidified brine should be poured hot onto the vegetables. 4. The filled cans and jars are then placed, with their covers in place but loose, on the false bottom of the boiler.
Hot water is then poured into the boiler until it reaches to about three-fourths of the height of the jars. A second tier may be placed on a rack resting on the first tier. 5. The boiler is then covered and heated to boiling, for one hour for most vegetables. Pumpkins, beans and corn require two hours. 6. After this heating remove and seal quickly, while still boiling hot, by screwing down the tops of the jars or applying the wax to the cans.
This is a thoroughly safe and satisfactory way of preserving vegetables. With some vegetables the acid may be omitted, but in this case two or three repeated heatings are necessary and this lowers the quality of the food to some extent.
Reheating is not practicable with waxtop cans.
This is a boiling-water-bath process applied to low-acid vegetables, and the gap between what it promises and what it delivers is the whole reason the page carries a warning. The notes below explain where the method fails rather than how to adapt it.
- The temperature ceilingA covered wash-boiler of water cannot exceed about 212F at sea level, and the recipe only fills it three-quarters up the jars, so the upper contents run cooler still. Clostridium botulinum spores in low-acid vegetables survive that indefinitely; they require roughly 240F, which only a pressure canner reaches.
- The brine is not a preservativeThree ounces of salt to a gallon of water is around 2 percent — a seasoning strength, not a curing strength. It has no meaningful inhibitory effect on botulinum spores in a sealed, oxygen-free jar.
- The acid is unmeasured where measurement is everythingSafety in acidified canning depends on the finished pH of the food, not on ounces of lemon juice per gallon of brine. Lemon and vinegar strength varied enormously in this period, packing density varied jar to jar, and the vegetables themselves buffer the acid, so the actual pH of any given jar is unknown.
- Corn, beans and peas are the worst casesThese are among the lowest-acid, densest-packing vegetables in the domestic kitchen, and heat penetrates a tight pack of cut corn very slowly. The recipe's two hours for beans and corn (peas get only one) does not compensate for being 28 degrees short of the required temperature.
- Intermittent processing does not workThe closing remark that the acid may be omitted if there are "two or three repeated heatings" describes the old fractional or tyndallisation method. Repeated boiling kills vegetative cells but leaves surviving spores in a warm, sealed, low-acid, anaerobic jar between heatings — close to ideal conditions for toxin production.
- Sealing after processingScrewing lids down or applying wax after the heat is finished can expose the headspace to kitchen air at the moment of closure — sealing boiling hot limits this, but there is no subsequent heat step. Modern practice seals before processing.
- There is nothing to taste or smellBotulinum toxin gives no reliable warning — a spoiled-looking jar is a mercy, an ordinary-looking one is not evidence of safety. This is why the confident line "a thoroughly safe and satisfactory way" is the most dangerous sentence on the page.
- What to use insteadFor canning any vegetable other than properly acidified pickles or tomatoes, follow a current USDA or extension-service tested process with a pressure canner. Freezing is the straightforward alternative for peas, beans, corn and squash.
Wash-boiler canning belongs to the American home-preserving campaigns of the early twentieth century, when extension agents, canning clubs and wartime food-conservation drives encouraged households to put up their own vegetables with whatever equipment they already owned — hence the improvised false bottom of wire netting or wooden grating, which kept jars off the hot metal base of the family laundry boiler. The acidified-brine method in step 3 appears to reflect period thinking: acid foods were known to keep safely in a boiling-water bath, and adding lemon juice or vinegar was reasoned to bring beans and corn into the same category, without any practical way for a home cook to verify the resulting pH. Botulism was described in the nineteenth century and the organism identified in the 1890s, but its link to under-processed home-canned vegetables was only being worked out in the years around the First World War, and pressure canners did not become standard domestic equipment for decades. Take that as a marker of how fast the science moved, not of carelessness on the author's part.