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Cochineal Colouring
Boil fifteen grains of powdered cochineal in half a pint of water, with a piece of alum about the size of a nut, and half a tea-spoonful of cream of tartar. Let the ingredients boil very slowly for half an hour; strain the liquid, and bottle it closely. Keep it in a cool place. It will keep better if three or four lumps of sugar are boiled with it. Sufficient for nearly half a pint.
A working stock of red food colour, made the way a Victorian kitchen made one: extract the dye from dried insects, fix it with a mordant, bottle it. It behaves like a homemade tincture rather than a modern bottled colour, so treat it accordingly.
- The weights, in modern termsFifteen grains is just under 1 gram of powdered cochineal. The book's half pint is an imperial half pint, about 285 ml; the yield of "nearly half a pint" allows for evaporation over the half-hour boil.
- "A piece of alum about the size of a nut"Genuinely ambiguous — anything from a hazelnut to a walnut, so roughly 3 to 10 g. Alum here is potassium aluminium sulphate, acting with the cream of tartar as a mordant to draw out and fix the colour, not as a flavouring.
- The hinge: slow, not hard, boilingHalf an hour at the barest simmer is what pulls the carminic acid out of the ground insect. A rolling boil drives off the water fast and concentrates the alum, which may leave a harsher, duller liquid.
- Strain properlyA sieve will not hold back the fine insect powder, which settles as grit and clouds anything you tint. Use a coffee filter or several layers of muslin, and expect it to run slowly.
- KeepingThis is an unpreserved water extract. "A cool place" meant a larder; refrigerate it, in a small, well-filled bottle, and reckon on a few weeks. The sugar lumps help a little by raising the solids, but discard at any sign of cloudiness, film or mould.
- How much to useThe original gives no guidance. It is strong: start with a few drops per pint of blancmange, jelly or icing and build up, judging the colour in the finished, set preparation rather than in the hot mixture.
- Cochineal todaySold as carmine or E120, still made from the same dried scale insects and still used commercially. Bottled carmine extract is more consistent and more stable than this; note also that carmine is a recognised allergen for a small number of people and is not vegetarian.
- Acid and alkali shift the colourCarminic acid is orange-red in acid and turns bluish-crimson as the pH rises. Added to a batter containing baking soda it will drift purple, which is why it suits cold jellies, creams and icings better than chemically raised cakes.
Cochineal is the dried body of Dactylopius coccus, a scale insect farmed on prickly pear in Mexico and Central America; the Spanish brought it to Europe in the sixteenth century, and for three hundred years it was often said to be among the most valuable cargoes crossing the Atlantic, prized first by dyers and only later by cooks. The alum-and-cream-of-tartar method here is straight out of the dyehouse, where those two mordants had long been used to fix reds on wool, and the kitchen simply borrowed the chemistry at a smaller scale. It belongs to a moment when shop-bought colours were under real suspicion — analyses had turned up genuinely poisonous mineral pigments in confectionery, and a jar of cochineal you had boiled yourself was the safe option.