Sweet versus Bitter Almonds

I had an interesting call this morning. A woman wanted to know whether Hall’s Hardy variety of almonds had to be processed to remove the cyanide to make them safe for eating. I knew apple, cherry, peach and nectarine seeds (all in the same family as almonds) have cyanide in them, but never gave any thought to whether almonds did. Rarely would we eat enough seeds of apples or peaches to get a toxic amount of cyanide. However, we often eat almonds in quantity without getting sick.

Could almonds be poisonous? I asked our Cooperative Extension nutrition and food safety specialist about this. She called the American Almond Board for information. Turns out there are sweet almonds and bitter almonds. The person at the Almond Board looked up Hall’s Hardy variety and couldn’t find it in any of their lists of sweet almonds. He suspects it must be a bitter almond rather than a sweet almond. Sweet domesticated almonds are grown commercially and due to a genetic variation from their bitter cousins, they do not contain the toxic chemical glycoside amygdalin, the precursor to hydrogen cyanide (prussic acid) that occurs in the bitter almond. Sweet almonds require very little processing to eat; although since 2007, there is a law in the U.S. that commercial almonds grown in the U.S., including those labeled “raw”, must be pasteurized to eliminate the risk of salmonella.

In bitter or wild almonds, the chemical compound becomes toxic hydrogen cyanide when the almond is crushed, chewed or injured with mechanical handling. Approximately 100-200 milligrams of cyanide when eaten can kill an average-sized person within minutes. Each raw bitter almond can produce 4 to 9 milligrams of hydrogen cyanide (Shragg et al, 1982. Western Journal of Medicine). Just a few handfuls of bitter almonds can kill a person; lesser amounts can cause serious health problems such as kidney failure.

Even with the danger, some people still grow bitter almonds for the almond extract oil used in sweets or cooking. Reducing the hydrogen cyanide requires crushing the seeds, drying the crushed seed powder into a cake, soaking it in water to break it up and then distilling the product. Yet, just 7.5 milliliters of bitter almond oil has resulted in death.

When I was unable to find anything definite on Hall’s Hardy, the caller checked with the nursery where she purchased the plant and was told it is an edible variety.