Mushroom Ketchup was being made before Tomato Ketchup.
You can still buy it today, made by George Watkins Co. in the UK. It’s much thinner than tomato ketchup, and more vinegary. You use it as you would a mushroom sauce. It’s great on meat pies and meatloaf.
The George Watkins brand contains vinegar, seasonings and mushroom powder.
Literature & Lore
To each peck of mushrooms 1/2 lb. of salt; to each quart of mushroom-liquor 1/4 oz. of cayenne, 1/2 oz. of allspice, 1/2 oz. of ginger, 2 blades of pounded mace.
Mode.—Choose full-grown mushroom-flaps, and take care they are perfectly fresh-gathered when the weather is tolerably dry; for, if they are picked during very heavy rain, the ketchup from which they are made is liable to get musty, and will not keep long. Put a layer of them in a deep pan, sprinkle salt over them, and then another layer of mushrooms, and so on alternately. Let them remain for a few hours, when break them up with the hand; put them in a nice cool place for 3 days, occasionally stirring and mashing them well, to extract from them as much juice as possible. Now measure the quantity of liquor without straining, and to each quart allow the above proportion of spices, &c. Put all into a stone jar, cover it up very closely, put it in a saucepan of boiling water, set it over the fire, and let it boil for 3 hours. Have ready a nice clean stewpan; turn into it the contents of the jar, and let the whole simmer very gently for 1/2 hour; pour it into a jug, where it should stand in a cool place till the next day; then pour it off into another jug, and strain it into very dry clean bottles, and do not squeeze the mushrooms. To each pint of ketchup add a few drops of brandy. Be careful not to shake the contents, but leave all the sediment behind in the jug; cork well, and either seal or rosin the cork, so as perfectly to exclude the air. When a very clear bright ketchup is wanted, the liquor must be strained through a very fine hair-sieve, or flannel bag, after it has been very gently poured off; if the operation is not successful, it must be repeated until you have quite a clear liquor. It should be examined occasionally, and if it is spoiling, should be reboiled with a few peppercorns. — Mrs Isabella Beeton. Book of Household Management. October, 1861. Recipe 472.