Cleaning seeds

Seeds are dispersed from their parent plants in a wide variety of ways and some germinate years later and great distances away. Some seeds are carried into the air in winged fruits or are blown great distances at the end of a feathery parachute. Many seeds may set out on their journey within a brightly-coloured wet fruit that is eaten by birds. Other seeds develop inside hooked fruits that are whisked from the maternal plants and onto the fur of passing mammals.

This diversity of dispersal systems poses a challenge for collectors and seed bank curators. Clean seed is sometimes collected in the field, for instance where the seeds are shed directly from a dry fruit capsule into the waiting seed bag. However, seed is usually collected when still within its fruit.

More information on seed cleaning (pdf)

Seed cleaning machines

A zig-zag aspirator

Once at Kew’s Millennium Seed Bank seed is cleaned to reduce bulk and the risk of disease. Releasing the seed unharmed from the diversity of fruit types requires great care and expertise. To limit damage, much of the work is done by hand using sieves. However, equipment such as an aspirator is used to winnow the debris from the heavier, filled seeds.

The role of a zig-zag aspirator

A zig-zag aspirator employs a similar technique to the ancient method of winnowing. Millennium Seed Bank curation staff use the aspirator to remove light material, such as debris and empty seeds from the collection.

The seed material is placed in a hopper at the top of the machine and falls into an airflow, which can be adjusted according to the size and weight of the seeds. Healthy seeds with full contents will be sorted into the ‘heavy fraction’. The ‘light fraction’ is checked for the presence of good seed before it is discarded.