Herbaceous plant originally from the Middle East, but today widespread
throughout the world because of the large consumption of
the edible bulb, the only part used. The stalk can reach approximately
1 m (39 in.) in height. The bulb consists of several concentric
tunics. Onion has a strong, pungent, lasting odor and a
characteristic onion flavor.
The essential oil is obtained by distillation of the bulbs with yields
of about 0.02%. The physical-chemical constants vary widely,
depending on the origin of the plant. The oil is a yellowish liquid
with a characteristic onion odor. Main constituents of the oil are
d-n-propyl disulfide and methyl-n-propyl disulfide.
The derivatives are oleoresin, fluid concentrated water extract, and
the fluid extract. The first two derivatives are obtained by special
manufacturing processes from thermally pretreated bulbs in order
to enhance some flavor top notes, as well as the flavoring strength.
