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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Preserved Mushrooms
Choose the largest button-mushrooms and wash them in vinegar, place them on a fine sieve, sprinkle with a small quantity of salt, and allow them to drain. Then place them in a deep dish in a cool oven, and in about an hour's time drain them again. Pour all the juice that ran from them into a lined stewpan, mix with a blade or two of mace, and then boil until reduced to half its original quantity; move it from the fire and let it get cold. Put the mushrooms into large earthenware jars, and pour the cold liquor over them. Melt some suet in a stewpan, and pour a layer of it on each jar; when cold and hardened cover the jars with bladder, tie them down, and keep them in a dry store-cupboard.
This is a nineteenth-century larder method: low-acid vegetables sealed under fat and stored at room temperature for months. It is the textbook set of conditions for Clostridium botulinum, and no adjustment of times or quantities in the original makes it sound.
- Why this one failsMushrooms are a low-acid food, around pH 6. The brief wash in vinegar does not acidify the flesh, and the concentrated cooking liquor is not an acid brine. Nothing here brings the contents to a temperature or acidity that destroys spores.
- The suet seal is the hazard, not the protectionA hardened layer of rendered fat excludes air, which is exactly the condition botulinum spores need in order to germinate and produce toxin. The seal that made the jars look sound is the thing that makes them dangerous. Botulinum toxin may give no smell, no swelling and no off taste, so a jar like this cannot be judged safe by inspection.
- A cool oven does not preserveThe recipe says only 'cool oven', which in period usage means a low, slack heat well below any sterilising temperature. It is used here to draw the juice out over an hour, and the mushrooms are then covered cold with cold liquor.
- BladderThe cover is a piece of cleaned animal bladder, softened in water, stretched over the jar mouth and tied; it shrinks tight as it dries. It has no modern equivalent and no reliable seal integrity.
- Button-mushroomsBy 1896 these would commonly have been cultivated Agaricus, close to a modern supermarket white mushroom, though wild-gathered field mushrooms were also sold as mushrooms. Identification adds a further unknown to any attempt at reconstruction.
- MaceA 'blade' of mace is one dried piece of the lacy aril surrounding a nutmeg seed. It is a flavouring only and contributes nothing preservative.
- If you want preserved mushroomsUse a current tested recipe from a food-safety authority: either a properly acidified vinegar pickle for the refrigerator, or freezing after cooking. Shelf-stable mushrooms require pressure canning to a validated schedule.
Potting under fat was the standard English answer to a glut before reliable canning, and it was applied to everything from shrimps and beef to mushrooms; the same shelf held mushroom ketchup, made from a related salted mushroom liquor, though typically spiced and usually vinegared. Oscar Tschirky's The Cook Book by "Oscar" of the Waldorf (1896) is enormous and encyclopaedic rather than tightly edited, and it carries a good deal of inherited English household material of this kind alongside the hotel's own restaurant cookery. Entries like this one belong to a kitchen that had a cool dry store-cupboard, a butcher supplying suet by the pound, and no refrigeration to speak of. Botulism had been described as a food hazard by Kerner from sausage poisoning in the 1820s, and the organism itself was identified by Van Ermengem in the 1890s, but its link to home-preserved low-acid foods was not widely understood for decades after this book appeared, which is why a cook of Oscar's standing could set it down without hesitation.