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: Tomatoes
Stewed Tomatoes. - These keep very easily even in the common screwtop jar. Hence such jars may be set aside for tomatoes and the more modern styles used for canning other vegetables. In this case observe that the tops and rubbers must first be sterilized by placing them in cold water. Bring to a boil and boil for ten minutes. Handle as little as possible, especially the inside of the top or inner edge of the rubber.
Fill the jar with the cooked tomatoes while steaming hot, put on the rubber, screw the top down firmly, invert it and let it stand in that position until cold. To prepare the tomatoes, wash and plunge them in boiling water for five minutes. Now dip for a moment in cold water, pare, slice and place them in a preserving kettle over an iron ring or tripod. Heat slowly and stir frequently from the bottom. Bring to a boil and then boil thirty minutes. Put in sterilized jars and seal.
Whole Tomatoes. - Use 8 quarts of medium sized whole tomatoes and 4 quarts of sliced tomatoes. Prepare the sliced tomatoes as for stewed tomatoes. Boil twenty minutes, rub through a strainer and return to the fire. Now pare the whole tomatoes and put them in sterilized jars. Pour over them the stewed and strained tomatoes until the jar is full. Put the uncovered jars in a moderate oven on a pad of asbestos, or in a shallow pan of hot water and cook for half an hour. Remove, fill to overflowing with boiling hot strained tomatoes and seal. Any strained tomatoes left over may be canned for sauces.
How to Open a Jar.-Run a thin knife blade under the rubber next to the jar and press against the jar firmly. If this does not let in enough air to release the pressure on the top, place the jar in a deep saucepan of water, bring to a boil and keep boiling a few minutes. It will then open easily.
This page gives two open-kettle canning methods for tomatoes, plus an oven-processing step. Neither approach meets any current standard, and the reasons are specific rather than general.
- Open-kettle sealing is the central failureFilling hot jars, screwing the lid down and inverting them relies on the cooling contents to pull a vacuum. Nothing sterilizes the headspace, the jar rim or the air trapped inside, and the boiling point of the tomatoes never exceeds 212F. That is well below the 240F needed to destroy Clostridium botulinum spores in a low-acid pack.
- Tomatoes are not reliably acidicTomatoes sit near pH 4.6, the line below which botulinum cannot grow, and some varieties, along with any overripe or frost-touched fruit, can test above it. Current guidelines require added bottled lemon juice or citric acid in measured amounts before a timed water-bath or pressure process; this recipe adds no acid and specifies no process temperature.
- Oven canningThe "moderate oven" step for whole tomatoes (roughly 350F by period usage) heats jars through dry air, which conducts heat poorly and unevenly. The contents may never reach boiling while the glass is stressed enough to crack or burst. Oven processing has been advised against for decades.
- The asbestos pad"A pad of asbestos" was sold as heat-diffusing equipment in kitchens of the period, and appears here without comment. Asbestos fibre is a known carcinogen and any surviving pad or mat should be treated as hazardous material, not put under a jar.
- Zinc screw tops and rubber ringsThe "common screwtop jar" of this period used a zinc cap over a rubber gasket, reused season after season. Old rubbers take a set and stop sealing, and the seal cannot be checked by the flat-lid button test used with modern two-piece closures. These jars are collectibles, not equipment.
- Toxin is invisibleBotulinum toxin produces no off smell, no cloudiness and no gas in many cases, so a jar that looks and smells sound is not evidence of safety. It also survives refrigeration; only sustained boiling degrades it, and no one should be relying on that.
- If you want canned tomatoesUse a current USDA or extension-service recipe with specified acidification, jar size, headspace and process time. The historical text is worth reading for what it shows about period practice, not for use.
Tomatoes were a mainstay of nineteenth-century American home canning, and this passage shows why: they were cheap, arrived all at once in enormous quantity, and were believed to be acidic enough to keep in whatever jars were on hand. That belief is exactly what makes the entry dangerous now. The self-sealing glass fruit jar with a threaded neck is generally credited to John Landis Mason in the 1850s, and by the time Household Discoveries was compiled such jars were so ordinary that the author can casually recommend setting the older, less trustworthy ones aside for tomatoes and saving the "more modern styles" for other vegetables. Botulism from home-canned produce was not understood as a distinct hazard until well into the twentieth century, and the systematic laboratory work behind pressure canning and acidification schedules came later still, which is why a careful, methodical writer of the period could describe a procedure that no extension office would sanction today.