Bitter almond

Bitter almond trees look almost identical to sweet almond trees, with pink-white spring blossom and a fuzzy, green, leathery fruit that splits to reveal the stone. The kernel is a little shorter and broader than the sweet almond, but the main difference is flavour.

When chewed, bitter almond tastes intensely bitter and has the sharp, sweet-cherry aroma used in marzipan. That flavour arises when amygdalin in the seed is broken down and releases benzaldehyde, and also hydrogen cyanide.

Raw kernels are not sold as a food in many countries. Commercial products include flavoured extract, essential oil with cyanide removed, and apricot kernels as a substitute.

The almond is native to the Middle East and Central Asia, from Turkey and Iran to the mountains of Central Asia, and it was among the earliest tree crops domesticated, more than four thousand years ago. Wild almonds are naturally bitter, and the sweet form arose from a mutation that lowered amygdalin production.

Bitter almonds are therefore the older, ancestral type, and bitter trees remain in orchards at low frequency, since the characteristic is controlled by a single gene.

The name almond is from Old French almande, from Latin amygdala, itself from Greek. Amygdalin, the compound responsible for the bitterness, is named after the same word.

Bitter almonds have been valued for flavour and feared for toxicity for a very long time. Ancient Egyptian, Greek and Roman writers recorded their use in perfumes, cosmetics and medicine, and also noted their poisonous effect on animals and people.

In medieval and Renaissance Europe, bitter almonds were used in marzipan, sweets and sauces, with the small proportion of bitter kernels blended with sweet to give flavour. The Italian liqueur amaretto and amaretti biscuits traditionally depend on bitter almond or apricot kernel.

By the 19th century, chemists had isolated amygdalin, and bitter almond oil became an important flavouring and a component in perfumery, until safer synthetic benzaldehyde replaced it.

Regulation today commonly restricts the sale of raw bitter almonds. European and other authorities set limits on the cyanide in foods, and many producers use debittered kernels, apricot kernel extracts or synthetic flavour in marzipan and amaretto.

Small amounts of bitter almonds or their extract have traditionally been combined with sweet almonds in marzipan, macaroons, amaretti biscuits and almond liqueurs such as amaretto. Their aroma is the origin of the classic almond essence.

Debittered or heat-treated kernels are sometimes used in baking, and cold-pressed bitter almond oil with cyanide removed is used in cosmetics and massage.

In traditional Middle Eastern and South Asian medicine, almond oil from bitter kernels was used externally and, rarely, internally in tiny quantities.

There is no reliable evidence for health benefits of eating raw bitter almonds, and the risks outweigh any suggested value. The kernels are a source of the glycoside amygdalin, which is sometimes marketed as laetrile or vitamin B17, a substance that has not been shown to treat cancer and has been linked to cyanide poisoning.

Sweet almonds, in contrast, are well studied as a source of unsaturated fat, protein, vitamin E and fibre.