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Salt Butter, to Make
The common method of preserving butter is by salting it more or less. Salt is thoroughly worked into the butter, in the proportion of one or two ounces to the pound, according as the butter is required to be kept for a shorter or longer time. Dr. Anderson, in his "Recreations," recommends another method of curing butter, by which, he says, with ordinary care, it may be kept for years in this climate, or carried to the East Indies, if packed so as not to melt. "Mix two parts of the best salt, one of sugar, and one of saltpetre, and beat them into a fine powder: one ounce of this preparation is sufficient for a pound of butter. This should be thoroughly mixed with the butter as soon as it is separated from the whey, and it should then be put into a clean cask. It should be packed very well down, to exclude the air thoroughly, the top should be covered with a sprinkling of salt, and melted butter poured over it to fill up every crevice before the cover is fixed down. Butter cured in this manner does not taste well till it has stood at least a fort-night after being salted; but after that time it has a rich marrowy taste that no other butter ever acquires, and tastes so little salt that one would imagine it would not keep." Dr. Anderson had seen it perfectly sound when two years old in this climate.
This is a preserving formula rather than a dish, and the second method in particular belongs to the history of food preservation rather than to any current kitchen. The reasons are specific.
- The saltpetre is far out of rangeOne ounce of the mixture per pound of butter means roughly a quarter-ounce of saltpetre (potassium nitrate) per pound — on the order of 15,000 parts per million. Modern curing practice works in hundreds of ppm of nitrate or nitrite, and only in meats where the residual level is controlled and measured. There is no safe way to scale this by eye.
- Nitrate belongs in cured meat, not butterSaltpetre's preserving action depends on reduction to nitrite by bacteria in a meat cure. In butterfat it serves no comparable function, so the dose here delivers the hazard without the purpose.
- Raw cream, held for yearsThe butter is worked "as soon as it is separated from the whey" — unpasteurised, never heated, and then sealed in a cask at ambient temperature for months. Nothing in the process reaches a temperature that inactivates Listeria monocytogenes or the pathogens carried by raw milk.
- Sealing under melted butter is not a safe sealFilling the crevices with melted butter and clamping a lid excludes oxygen without excluding spores. Anaerobic storage of a low-acid food at room temperature is a condition under which Clostridium botulinum can be a concern, and nothing here is measured.
- The taste note is a warning, not a recommendationAnderson observes that the butter "tastes so little salt that one would imagine it would not keep." That is the point: the perceived saltiness gives no reading of the actual water-phase salt concentration, which is what determines whether anything is inhibited.
- The plain methodSalting at one to two ounces per pound — the opening of the entry — is simply salted butter, and is a real historical practice. The text specifies nothing about the provenance of the milk or the conditions of storage. For salted or cultured butter today, work from a current recipe with pasteurised cream and refrigerated storage.
Salt was among the few practical means of carrying butter through a winter or across an ocean, and the trade in barrelled salt butter — from Ireland, the Netherlands and the Baltic — was one of the great provisioning industries of the eighteenth and nineteenth centuries. The doctor cited here is James Anderson (1739-1808), the Scottish agricultural writer whose Recreations in Agriculture, Natural History, Arts, and Miscellaneous Literature appeared in six volumes from 1799; his sugar-and-saltpetre cure was widely reprinted through the following century and turns up almost verbatim in later household manuals. The mention of the East Indies indicates the purpose: butter that could survive a voyage round the Cape without rancidity was worth real money, and the sugar is generally taken to have softened the harshness of heavy salting. That such a compilation was still repeating a formula three-quarters of a century old says less about its merit than about how household books were assembled — each borrowing from the last, long after refrigeration and rail had made the problem it solved largely obsolete.