Buried in the bookseller's description of an anonymous Regency-era English manuscript receipt book is a small, telling detail about what early-19th-century households kept in their pantries:

"Cowslip seems to have been a favourite, and there are multiple receipts for Noyeau. There is Lethe (probably an aptly named concoction, with prices given for the ingredients, lemons, brandy and sugar), Everton Toffee, and Transparent Pudding."

The book itself is a hand-written collection of recipes ("receipts" in period English) compiled in several female hands between roughly 1802 and 1849, on paper watermarked 1802, bound in purple half roan over marbled boards. It is mostly culinary, with a smattering of medical and household entries — exactly the kind of working-document that real households cooked from.

What jumps out is Noyeau (modern spelling: noyau, French for "kernel" or "stone"). The fact that an ordinary English household had multiple recipes for it tells us this was as routine as keeping a few vermouth recipes today. And what was noyau? A sweet cordial made by steeping the cracked kernels of apricots, peaches, cherries, or bitter almonds in brandy and sugar.

Here is the forgotten part: those kernels contain amygdalin, which the body metabolizes into hydrogen cyanide. The same compound that gives marzipan and amaretto their distinctive bitter-almond flavor is, in higher doses, lethal. A glass or two of properly diluted noyau was harmless and pleasant. A heavy hand with the kernels could send you to bed permanently.

Regency cooks knew this empirically. Recipes from the period typically specified small numbers of kernels per quart of brandy, long maceration times, and careful straining. The knowledge of how much was too much was passed mother-to-daughter, written in books exactly like this one.

• By the late 19th century, public-health concerns and the rise of commercial liqueurs pushed homemade noyau out of the kitchen.
• Today, the FDA warns against apricot-kernel supplements (sold dubiously as "Vitamin B17" cancer cures) because people have died from cyanide poisoning following the dosages on the package.
• Crème de Noyaux survives as a niche bar ingredient — most modern brands now use artificial almond flavoring rather than real kernels, precisely to sidestep the cyanide problem.

The closest thing a modern drinker has tasted is probably the bitter-almond note in an Aviation cocktail, or the marzipan in stollen at Christmas. Both are pale echoes of a once-common home liqueur that required genuine craft knowledge to produce safely.

It is striking how casually the description treats it: "multiple receipts for Noyeau," as ordinary as multiple recipes for chocolate-chip cookies would be in a modern recipe binder. The technique was so commonplace it warranted no special warning. When it fell out of practice, it took with it a small body of dose-empirical knowledge that the FDA is now, two centuries later, trying to re-establish in the form of warning labels.