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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Milk and Cream, to Preserve
Add one ounce of sugar to one pint of milk, and boil it down to one-half. Run it into small bottles, and put them in a pan of cold water placed on a good fire. Allow the water to boil for an hour, and then, while still hot, close the mouths of the bottles with very good and tight-fitting corks, and let the contents become cold. When cold, dip the corks and necks of the bottles in a ladle containing melted sealing-wax or common pitch, so as to render the corks perfectly air-tight. Cream is preserved by evaporating it down to a quarter of its previous bulk, without adding sugar, and then preserving it in bottles as directed for milk. The bottles containing it should, however, only be boiled for three-quarters of an hour.
This is a home-canning procedure for milk and cream, and it cannot be made safely by any adjustment of the method described. The notes below explain where it fails rather than how to fix it.
- Milk is a low-acid foodMilk sits around pH 6.7, well above the 4.6 threshold below which Clostridium botulinum cannot grow. Sealed airtight in a bottle, it is close to an ideal anaerobic culture medium, and the toxin produced is among the most lethal substances known.
- Boiling water cannot sterilise itAn hour in a pan of boiling water reaches only 212F (100C). Botulinum spores routinely survive that; destroying them reliably requires roughly 240-250F, which is only achieved under pressure. The three-quarter-hour bath for cream is weaker still.
- The sugar is not a preservative hereOne ounce of sugar to a pint of milk reduced by half comes nowhere near the sugar concentration of commercial sweetened condensed milk, where sugar is high enough to bind the available water and inhibit growth. At this level it flavours the milk and does nothing more.
- Cork and pitch are not a sealCork and pitch are not a reliable seal -- A driven cork dipped in sealing-wax or pitch gives no dependable hermetic closure, so spoilage organisms can enter if the seal fails as the bottle cools and contracts. It also gives no visual sign of failure: there is no lid to buckle or hiss.
- Botulism gives no warningToxin-contaminated milk need not smell, look or taste wrong. Tasting to check is not a safety test, and heating a suspect bottle is not a remedy a home cook should be relying on.
- Bottles in direct heatGlass bottles set in a pan on "a good fire" and then handled while still hot are a thermal-shock and scalding hazard quite apart from the microbiology.
- If you want the productBuy evaporated milk, which is heat-sterilised under pressure in the can, or sweetened condensed milk, which is preserved by its very high sugar concentration; or use a current USDA-tested recipe. Milk and cream are not among the foods home canning can handle.
Cassell's gave space to this because in the 1870s and 80s the problem of keeping milk was genuinely urgent: urban households bought from carts and dairies with no cold chain, and milk was both perishable and a notorious vehicle for disease. Reducing it over heat and sealing it in corked bottles was the domestic imitation of a commercial process then still new condans... condensing milk in vacuum pans is generally credited to Gail Borden in the 1850s, and factory-made tinned milk spread quickly in the decades after. What the household version lacked was the sealed tin and, more importantly, the temperature: the connection between anaerobic canned low-acid food and Clostridium botulinum was not established until the early twentieth century, and pressure canning only became standard home advice later still. The recipe is a fair record of what careful cooks believed sufficient, and a good illustration of how much of food safety is invisible to the senses the book relied on.