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Greening for Soups
Wash a handful of young spinach-leaves, pound them in a mortar, put the bruised leaves into muslin, and squeeze out as much juice as is required. The soup may be heated, but must not be brought to the boiling point after the juice is added, or the green will be converted into a dirty yellow.
This is a colouring preparation rather than a dish in itself — raw spinach juice used to green a soup or sauce at the last moment. It works, but only if the heat is kept under control.
- The hinge: never let it boilChlorophyll degrades to pheophytin once heat and acid get at it, turning the fresh green to olive-brown — the "dirty yellow" of the original. Add the juice off the heat, or with the pan barely steaming, and serve promptly; the colour fades within minutes of sitting hot.
- "A handful" and "as much as is required"Genuinely open-ended; the recipe gives no quantities at all. A generous handful of spinach yields only a small amount of juice — a tablespoon or two — and a little goes a long way in a pale soup. Add it a teaspoon at a time and judge by eye.
- Mortar and muslinA blender or food processor with a splash of water does the pounding faster; press the pulp through a fine sieve lined with muslin or a coffee filter, or wring it in a clean tea towel. The point of the muslin is to keep leaf fibre out of a clear soup.
- Use young leaves onlyMature spinach is more bitter and more oxalic; young leaves give a cleaner flavour as well as a brighter juice. Wash thoroughly — grit survives pounding perfectly well.
- The older "green butter" versionSome kitchens heated the juice gently until the chlorophyll coagulated, then skimmed off the green curd and worked it into butter for keeping. That paste is more stable than raw juice but has the same enemy: a rolling boil.
- Suitable soupsOnly for pale bases — veal, chicken, fish, pea or potato purées. On anything already brown or tomato-based the effect is invisible and the vegetal note simply muddies the flavour.
- Make it to orderThe juice oxidises and loses colour on standing, so it will not keep. Extract it while the soup is finishing.
Colouring food was routine work in the Victorian professional kitchen, and period manuals commonly list a set of standard tints: cochineal or beetroot for red, saffron or egg yolk for yellow, caramel for brown, and spinach for green. The French term for the preparation was vert d'épinards, and the technique of pounding leaves and pressing out the juice appears in French kitchen literature; a related beurre vert, in which the coagulated green is worked into butter, belongs to the same French repertoire. Appearance was treated as a technical matter on a par with seasoning, and a green soup that arrived at table looking khaki counted as a fault in the cook, not the ingredient.