There are two main species of the Almond plant. One form called “sweet almonds” is by far the most common form of almonds eaten today. The other specie of almond is called a “bitter almond”. The bitter almond is rather broader and shorter than the sweet almond and has an astringent, bitter flavor. It is open to conjecture but some researchers believe the early form of almond was more closely related to the bitter form and it has been by selective breeding that the sweet form has become the most common form of almond consumed today. It is the presence of the soluble glycoside Amygdalin in bitter almonds that differentiates the two forms of almond.
Bitter almonds contain approx 2%-4% of the soluble glycoside Amygdalin which in the presence of water and the enzyme beta glycosidase (Emulsin) releases glucose, hydrocyanic acid (Prussic acid) and benzaldehyde. Bitter almonds may yield from 4–9mg of Hydrogen Cyanide per almond. It is the Benzaldehyde is responsible for the bitter astringent taste while the Hydrogen Cyanide is responsible for the almond aroma. See our information on cyanide poisoning.
Amygdalin → Benzaldehyde + Hydrocyanic acid + Glucose
As early almonds may have been more closely related to bitter almonds it was found that boiling (blanching) and roasting the almonds made them more palatable and pleasant to eat. Early records describe how deaths sometime occurred in children when they ate bitter almonds. Today we know that these two treatments denatures the enzymes beta glycosidase (Emulsin) which is required for the production of the hydrogen cyanide and benzaldehyde and with these products not being produced the almonds had a milder non bitter taste and did not cause illness from cyanide poisoning. It is also possible that green almonds may also possess some Amygdalin but the amount produced appears to decrease as the almond matures. The actual mechanism for this reaction pathway is not readily understood.
Amygdalin ↛ Benzaldehyde + Hydrocyanic acid + Glucose
No reaction as enzyme has been denatured and is unable to react with the Amygdalin substrate. See practical Sheet “Test for HCN in Almonds” .