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Preserved Green-Corn
Select very full ears of tender corn, remove the husk and silks, cut the corn from the cob with the back of a knife, pack it in glass jars, filling them and pressing the corn down, and then close them with rubber and porcelain-lined covers. Place some laths across the bottom of a large boiler, and fill it with jars of corn, laying a little straw or hay against each to prevent them from knocking against one another during the boiling. Pour in sufficient cold water to cover the jars to half their height, place the boiler over the fire with a cloth, and the cover over it, and boil the corn continually for three hours, being careful to see that there is water enough to furnish a full volume of steam. Take up the jars and screw the covers as tightly as possible. When the jars are cold again screw the covers, and keep the corn in a cool, dark place. Mango, Preserved Put a hundred or so medium-sized green mangoes into a bowl of cold water to steep; grate off the outer coat very fine, cut them lengthwise in order to remove the stones, and throw them into weak lime-water. Put them into a preserving-pan with enough water to cover, parboil, skimming frequently; then turn them out onto a sieve and drain. Have ready a sufficient quantity of syrup, made of eight pounds of sugar, put in the mangoes and let them simmer in this, removing all the scum, until the sugar commences to crystallize; then remove the pan from the fire, allow the contents to cool, put the mangoes and syrup into wide-mouthed bottles or jars, and cork down when quite cold. Let them remain for two or three days, and should the syrup be getting thin, reboil it, adding the mangoes for a few minutes at the end of the boiling, and bottling again. This process should be repeated until there is no further sign of fermentation, corking down when quite cold. This preserve will remain good for a number of years if kept in a cool dry place. Enough syrup should be prepared at first, so that on the completion of the boiling there will be enough to cover the mangoes.
Two preserves are run together here, and the first of them is the reason this page carries a warning. Sweet corn is the classic low-acid vegetable, and the method given cannot make it safe.
- Why the corn failsCorn has a pH around 6.5 and is dense enough to trap air. Clostridium botulinum spores survive hours at 212F, which is the highest temperature this water bath reaches, and the sealed jar then gives them the oxygen-free, low-acid, room-temperature conditions they need to produce toxin. Three hours of boiling only softens the corn; it does not sterilise it.
- Half-submerged jarsThe jars sit in water to half their height and are cooked partly in steam under a cloth-covered boiler. Heat penetration into a packed jar of corn under those conditions is uneven and unmeasured, so even the 212F ceiling is not reliably reached throughout the jar.
- Tightening after processingScrewing the covers down after the jars come out of the boiler, then again when cold, is what this recipe directs and it appears in other manuals of the period; it is now understood to be a way of producing a false seal that looks sound and is not. Botulinum toxin may give no smell, no gas and no off taste in corn.
- If you want canned cornHome-canned corn requires a pressure canner at 240-250F for a tested time, with a current tested procedure from a food-safety authority. Use one of those, not this.
- The vessels described"Laths" are thin wooden strips used as a rack to keep glass off the hot metal bottom; a "boiler" is the large lidded wash boiler that sat across two stove holes. "Porcelain-lined covers" are zinc screw caps with a white glass liner, sealed against a separate rubber ring.
- Cutting corn with the back of a knifeScraping with the back of the blade presses the milky interior out of the kernels while leaving much of the tough hull on the cob, which would give a dense, creamy pack rather than whole kernels.
- The mango preserveThis is a different proposition: green mangoes simmered in a syrup made from eight pounds of sugar, reboiled whenever the syrup thins. Preserves heavy in sugar keep far better than low-acid vegetables, and the repeated reboiling concentrates the syrup as water is driven off. A hundred mangoes is a very large batch; scale by keeping enough syrup to cover the fruit.
- Lime-water for the mangoesThe weak lime-water is a firming bath -- calcium hydroxide sets the pectin so the slices hold their shape through long simmering. Pickling lime is still sold for this purpose; the recipe parboils and drains the fruit rather than rinsing it, though modern practice is to rinse thoroughly.
Oscar Tschirky's 1896 book was written for a hotel kitchen that still preserved its own summer produce, and the green-corn entry is a straightforward copy of the domestic practice of the day: pack, boil for hours, tighten, hope. Corn was one of the two foods -- with home-canned string beans -- that would go on to account for a large share of American household botulism cases once bacteriologists began tracing outbreaks in the 1910s and 1920s, and it was that work that produced the tested processing schedule and the push to use pressure canning. The mango preserve beside it points the other way, toward tropical fruits, put up by repeated boiling in heavy sugar until nothing can ferment.