Winnowing and yandying: separating seed from husk and sand

The idea

First Nations Australians separate seed from husk by winnowing (air carries off the lighter husk) and from sand by yandying (shaking a tilted dish sends small dense grains to the bottom), each technique exploiting a difference in density and particle size.

What you need

• a shallow, curved wooden or plastic dish about 40 cm long to stand in for a yandy (a real coolamon only on loan and with the permission of the community that made it)
• two mixtures per group, weighed: 25.0 g of clean seed (bushfood wattle seed or dried lentils) with 20.0 g of husk or bran for winnowing, and 25.0 g of the same seed with 30.0 g of fine dry sand for yandying
• desk fan on its lowest setting or an outdoor breeze, a large tray or sheet to catch what falls, two containers
• balance reading to 0.1 g, sieve with holes smaller than the seed, eye protection

How to do it

1. Before the lesson, the teacher seeks advice from the local Aboriginal Education Consultative Group or school Aboriginal Education Officer about how the techniques and their names are presented.
2. Calculate the starting purity of each mixture (mass of seed divided by total mass).
3. Winnowing: pour the seed-and-husk mixture slowly from about 30 cm into a container on the tray, with the fan blowing across the falling stream. Pour from container to container three times, then weigh the product.
4. Yandying: put the seed-and-sand mixture in the dish, tilt one end up slightly and shake gently back and forth for 2 minutes. Scoop the seed from the upper layer into a second container and weigh it.
5. Sieve out the remaining sand and pick out the remaining husk from each product, and weigh the clean seed.
6. Calculate the final purity (mass of clean seed divided by mass of product) and the recovery (mass of clean seed divided by 25.0 g) for each technique, and name the property each one depends on.

What you should see

The starting purities are 55.6 percent seed for the winnowing mixture and 45.5 percent for the yandying mixture. Winnowing: the husk, light for its size, is carried downwind onto the tray while the seed falls nearly straight down, so the product is far purer than the start. Yandying: the fine, dense sand works down to the lowest part of the dish and the larger seed rides on top where it can be scooped off. The learner knows it worked when both final purities are well above the starting purities, most of the 25.0 g of seed is recovered, and the learner can say which property (the air resistance of the husk for its mass, the size and density of the sand grains) each technique uses.

What changes

What you change

separation applied (none, winnowing, yandying)

What you measure

purity and recovery of the seed

What you keep the same

• starting mass of each component
• fan setting and pouring height
• number of pours and shaking time
• same dish

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• Heavier things always fall faster, so the wind cannot separate seed from husk.
• Traditional techniques are not science because they were not written down.
• Shaking a mixture always mixes it more rather than separating it.

Safety card

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Science 7–10 Syllabus (2023)SC4-SOL-01SC4-WS-04
• Australian Curriculum v9AC9S7U06AC9S7H02

Sources

The pages the author read to write this activity.

1. curriculum.nsw.edu.au/learning-areas/science/science-7-10-2023/outcomes
2. www.australiancurriculum.edu.au/support-resources/background-information/science_teacher_background_information_AC9S7U06_E6
3. curriculum.nsw.edu.au/learning-areas/science/science-7-10-2023/content/stage-4/fa8f5a0412