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OYSTERS, KETCHUP OF (another way)
Take half a pint of freshly-shelled oysters, clean them well, carefully removing the beard and the gut, and pound them in a mortar to a smooth paste. Add half a pint of sherry, and a salt-spoonful of powdered mace, a salt-spoonful of pepper, and half an ounce of salt, and boil all gently together for twenty minutes. Strain the liquid, and mix with it a tea-spoonful of brandy, then bottle the ketchup, and resin the corks. Probable cost of oysters, 1s. 6d. to 3s. per dozen.
This is a bottled shellfish preserve, and that is the problem with it. The notes below explain the vocabulary and the costings, and then why the method cannot be followed.
- Why it fails: anaerobic seafood at room temperaturePounded oysters sealed under a corked, resin-capped stopper and kept on a shelf is a textbook environment for Clostridium botulinum, which grows without oxygen and produces a toxin that is not detectable by smell or taste. Twenty minutes at a gentle boil kills vegetative bacteria but does not destroy the spores, and nothing here reliably prevents them germinating afterwards.
- Why it fails: no measured aciditySafe shelf-stable preserving of a low-acid food depends on either a measured pH at or below 4.6 or a pressure-canning schedule. This recipe has neither. The mace, pepper and brandy contribute nothing to acidity, and there is no vinegar or lemon in it at all.
- Why it fails: the salt and alcohol are not enoughHalf an ounce of salt in roughly a pint of finished liquid is about 3 per cent by weight, well under the level that inhibits botulinum. The sherry starts at around 17 per cent alcohol, but it is halved by the oyster pulp and driven off further by twenty minutes of boiling. A teaspoon of brandy at the end is flavouring, not preservation.
- "Resin the corks"The bottle was corked and the cork end dipped in melted resin or sealing wax to exclude air. The contents were boiled, but twenty minutes at a gentle boil is not a sterilising process, so an airtight seal over a low-acid food is precisely the wrong combination. If you want an oyster sauce, use a current recipe with a stated shelf life and refrigeration.
- Beard and gutThe "beard" is the frilled mantle edge and gills; the "gut" is the dark digestive sac. The recipe does not say why they are taken out, and picking them out of half a pint of shucked oysters is fiddly work.
- The measures, for referenceHalf a pint imperial is ten fluid ounces, about 284 ml, or roughly a cup and a quarter in American measure. A salt-spoon is about a quarter teaspoon. Half an ounce of salt is roughly 14 g, or two and a half level teaspoons of fine salt.
- The costingOne shilling and sixpence to three shillings a dozen was the pre-decimal price of oysters at the fishmonger.
Ketchup in the nineteenth century meant a thin, dark, strongly savoury bottled liquid used to season made dishes, sauces and gravies, not the sweet tomato condiment that later took the name. The word is generally traced to a fermented fish or soy brine of Southeast Asia, borrowed into English in the late seventeenth century and applied to a whole family of English keeping sauces: mushroom, walnut, cucumber, anchovy and oyster among them. Cassell's gives several versions of each because a well-run Victorian kitchen expected a rank of such bottles on the store shelf, made in season when the ingredient was cheap and drawn on all year to give depth to a sauce or a stew. Oysters suited the purpose because they were abundant and inexpensive through most of the century, before overfishing and disease reduced the English beds and turned the oyster from a working household staple into a luxury.