Teacher Background Information

This elaboration provides students with the opportunity to understand how First Nations Australians’ knowledges about changes between states of matter are used in many processes and practices. The scientific knowledges of applying or removing heat to produce changes in states of matter are evidenced in many long-held and ongoing First Nations Australian practices, including the extraction of oils, medicinal therapies and cooking practices.

Aboriginal and Torres Strait Islander Peoples have long demonstrated an understanding of the scientific principle that matter comes in the form of solids, liquids and gasses and that these various states of matter have different properties. The application or removal of heat is related to changes in states of matter and Aboriginal and Torres Strait Islander Peoples have long used temperature to change the state of matter of a substance for a desired purpose. The application or removal of heat is employed in many different circumstances, including the preparation of foods and medicines, to obtain a desired state of matter or utilise its observable properties.

Aboriginal and Torres Strait Islander Peoples have knowledge about which plant species contain important therapeutic oils and how to extract the oil. Some plant oils are highly volatile and can be vaporised at temperatures below the boiling point of the oil. The controlled application of heat to such plant material results in the therapeutic compound being released in the vapour (steam).

Prior to colonisation, the Wiradjuri People of central New South Wales treated colds by building steam pits that were heated by fires, lined with Eucalyptus spp. leaves and overlaid with possum-rugs. The Eucalyptus spp. oil is vaporised through this process and inhaled as a decongestant treatment for coughs and colds. Melaleuca spp. (tea tree) is a plant that also contains important medicinal oils. The Yaegl Peoples of the Coffs Harbour region of New South Wales heat tea tree leaves to release the oil in the vapour to treat respiratory conditions by inhalation. Products containing Eucalyptus spp. or Melaleuca spp. oil continue to be used in this manner today for the treatment of colds and respiratory conditions. The Anindilyakwa Peoples of Groote Eylandt and Bickerton Island in the Gulf of Carpentaria boiled the fresh leaves of a species of Calytrix and inhaled the vapours to unblock the sinuses and clear head colds. The Ngarrindjeri Peoples of the Murray River region in South Australia developed a sauna-like therapy utilising the steam released from wet plant material.

Many Aboriginal Peoples also use heat from fires to vaporise plant oils from foliage, bark and wood, to use as insect repellent. The Ngarrindjeri Peoples in South Australia use the green foliage of the daisy-bush for this purpose, while the Gugadja Peoples of the Western Desert use the conkerberry bush to repel insects. Steam from heating water or from fires is also useful in making wood more pliable and is used in the manufacture of canoes and wooden implements such as spears. The Warnindhilyagwa Peoples of Groote Eylandt use steam and fire to cure wood to complete the construction of dugout canoes.

Aboriginal and Torres Strait Islander Peoples also applied heat to liquefy fats into oils, a process known as rendering. The application of heat to the fat of an animal results in a change of state from solid to liquid. Rendered oils have many useful properties, making the process of liquefying fats an important practice and the extracted oils highly valuable. On the western Cape York Peninsula, the Anguthimri and the Awngthim Peoples rendered stingray fat by heating it in a large bailer shell. The liquid oil has long been used as a treatment in the manufacture and repair of wooden implements such as the spear-thrower. In the Torres Strait, the Mabuygiwgal People of Mabuaig Island today continue the long-held practice of boiling the fat of turtles, liquefying the solid turtle fat into oil, and collecting and storing the resulting oil. Similarly, the Quandamooka Peoples of Minjerribah (North Stradbroke Island) in Queensland boil down the fat of the dugong to a liquid state and use the oil medicinally to treat ailments such as colds, aches and pains.

Aboriginal and Torres Strait Islander Peoples used the technique of cold-pressing to release oils from nuts. This process uses heat generated through friction to extract a liquid oil from a solid seed or nut. Prior to colonisation, the Miriam People of Mer Island in the Torres Strait extracted coconut oil through a process of scraping and straining. Candlenut oil was extracted by the Dingaal People of the Cape York Peninsula region and has long been used as a fixative for pigments on wooden implements. In the southwest of Western Australia, the Wiilman Peoples of the Noongar Nation pounded the seeds of sandalwood into oil for rubbing onto skin. The application of heat by Aboriginal and Torres Strait Islander Peoples to change solid animal fats into liquid oils demonstrates the long-held understanding of the properties of solids and liquids.

Other means of preparing and cooking food also utilised heat to change water into steam. Aboriginal and Torres Strait Islander Peoples understand that all foods contain water and the application of heat to food changes the state of water from liquid into gas. This knowledge is applied by Aboriginal and Torres Strait Islander Peoples in the preparation and preservation of food. For millennia, food has often been cooked through a process of steaming, either in ground ovens or by wrapping food in leaves to retain the moisture when cooking. Such processes demonstrate Aboriginal and Torres Strait Islander Peoples’ understanding that the water within the food will evaporate into gas when heated. This steam remains within the oven or wrapping to provide moisture in the cooking process.

Over millennia, the Barindji Peoples of south central New South Wales have cooked large animals in a ground oven into which hot stones were placed. The animal was then placed into the oven, covered with grass, more hot stones placed on top, and completely enclosed with earth. At various cooking intervals a hole was made in the oven and water was poured in to steam the food. The addition of water to the oven demonstrates the knowledge that the steaming process requires water, as a liquid to generate steam for cooking. The Bindal and Wulgurukaba Peoples of far North Queensland also cooked meats in dug out ovens using hot stones and covering the entire ground oven with earth. If an opening was noticed it was immediately covered to keep the steam trapped and the heat and moisture within. The Luritja People of the Central Desert use a species of Zygophyllum as a source of moisture to generate steam for cooking cress and other plant foods. To cook plants, the Zygophullum sp. is placed on hot rocks in the sand with the plants to be cooked sandwiched between another layer of Zygophullum sp. More hot stones are placed on top and the whole oven covered with wet sand. When the surface of the sand cracks the plants are recovered for consumption and the Zygophullum sp. is discarded. Alternatively, food may be wrapped in leaves, such as banana leaves or leaves of native ginger, or moistened paperbark, to steam on hot coals or ash. This ensures that the water content from the food remains contained during the cooking process, and that the steam is not lost to the atmosphere.

Aboriginal and Torres Strait Islander Peoples also use the knowledge of water evaporation to preserve foods. Prior to colonisation, the Mabuygiwgal Peoples of Mabuaig Island in the Torres Strait prepared strips of dugong in the dry season by dehydrating the meat in the sun. Cooked strips of turtle meat were elevated on sticks so that the heat of the sun could remove the water content through evaporation and preserve the meat. This supply of preserved food was then available in the north-west monsoon season or while travelling. The Gunditjmara Peoples of south west Victoria preserved eels and fish by smoking them in special hollowed out trees. This process uses heat from a fire set underneath hanging fish to evaporate water from the fish, to preserve them for trade or storage. In Central Australia, the Pitta Pitta Peoples desiccated (removed all water from) pituri, a narcotic sourced from the plant Dubosia hopwoodii. This was done by hanging the tops of the plant to dry in the heat of the sun, sweating the leaves beneath a layer of fine sand, and powdering the dried leaves in preparation for transport. Such long and enduring practices demonstrate how Aboriginal and Torres Strait Islander Peoples have used knowledge of states of matter to evaporate water from food and other resources.

This elaboration provides the opportunity for students to understand changes in state of matter through Aboriginal and Torres Strait Islander contexts. Aboriginal and Torres Strait Islander Peoples have long used temperature to change the state of a particular material for a desired purpose or to exploit the observable properties of matter. This elaboration provides students with the opportunity to learn how Aboriginal and Torres Strait Islander Peoples have long used, and continue to use, heat to change state for medicinal purposes, insect repellents, the preparation and preservation of food resources, and engineering wooden vessels and implements.