Important: Safety Warning
This page offers rules for telling edible mushrooms from poisonous ones. No such rules are reliable, and these identifications predate modern mycology. Deadly species closely resemble edible ones, and mistakes are regularly fatal. Never eat a wild mushroom on the strength of this text.
In addition, 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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Ketchup, Mushroom
Take large flap mushrooms, freshly gathered; put a layer in a deep earthen jar, then a layer of salt, and so on alternately. Let them remain two or three hours, then pound them well with the hands. Allow them to remain two days, stirring and mashing them well each day. Pour them into a stone jar, and to every quart add one ounce of whole black pepper. Stop the mouth of the jar, set it in a stewpan of hot water, and keep it boiling for two hours. Take out the jar, and pour the juice through a sieve, without squeezing the mushrooms, into a clean stewpan; let it boil gently for half an hour, then strain through a flannel. Add a table-spoonful of brandy to each pint of ket-chup; bottle, and, when cold, cork and seal. Keep in a dry cool place.
This is a genuine recipe — the salt-extracted mushroom liquor that stood behind most Victorian gravies — but as written it combines two hazards that cannot be engineered out with a tweak. The notes below explain the method and where it fails.
- Why it fails: foraged mushrooms"Large flap mushrooms, freshly gathered" means mature, open-capped field or horse mushrooms picked from pasture. Several deadly species, including members of Amanita, pass as field mushrooms to an untrained eye, and pounding them into an anonymous black liquor removes every chance of catching the error later.
- Why it fails: low-acid bottlingThe finished ketchup is a low-acid, salted vegetable extract sealed into corked bottles and stored at room temperature. The two hours in a stewpan of hot water reaches only boiling point, which does not destroy Clostridium botulinum spores; the sealed anaerobic bottle is exactly the environment in which they germinate and produce toxin.
- The brandy does nothingA tablespoon of brandy to a pint works out at roughly one per cent alcohol in the finished sauce. It was added for flavour and as a token preservative and has no antimicrobial effect at that dilution.
- The salt is unmeasured"A layer of salt" alternated with mushrooms gives no ratio, so there is no way to know whether the finished liquor is salty enough to inhibit anything. Nineteenth-century versions varied from lightly seasoned to brine-strong.
- What "flap" and "stone jar" meantA flap mushroom is simply a fully opened cap with exposed dark gills, prized for colour and depth of flavour. A stone jar is glazed stoneware; the recipe starts the mushrooms in an earthen jar and moves them to a stone one for the two hours of boiling.
- If you want mushroom ketchupUse a current recipe with measured acidification and refrigerated or frozen storage, or buy it — mushroom ketchup is still made commercially in Britain. Cultivated portobellos give the same dark, open-gilled liquor the original was after.
Mushroom ketchup is one of the older survivals of what "ketchup" originally meant: not a tomato sauce but a thin, dark, salty store sauce, the name generally traced to the Hokkien kê-tsiap, a fermented fish brine encountered by English traders in Southeast Asia in the seventeenth century. English cooks reproduced the idea with what they had — walnuts, oysters, anchovies and above all mushrooms — and by the eighteenth century mushroom ketchup was a common kitchen store, splashed into gravies, hashes and made dishes wherever a cook wanted savoury depth without more meat stock. It is an ingredient rather than a dish in its own right, the Victorian household's answer to what a modern kitchen gets from a bottle of Worcestershire sauce or a spoonful of soy. The salting-and-pounding stage is straightforward osmotic extraction, drawing the mushrooms' liquor out over two days before any heat is applied, which is why the yield is dark and concentrated rather than watery.