Distilling oils and hydrosols

Where can a question take you? For Sue Fergus and her students at Taranaki’s Toko School, questions about candle scents and what to do with lavender plants led to a Curious Minds Participatory Science Platform (PSP) application. Answers to these questions led to real-world science and maths opportunities and a business venture to produce plant-based cleaning products.

Distillation and hydrosols – scientific terms more often associated with curriculum levels 7 and 8 than ages 7 and 8 – became everyday words for the learners as they worked with scientist Jim Bennett of Still Valley, Liz Sinclair of Pihama Lavender and local gardener Sue Rine.

Connecting curiosity with local experts

A scented candle and the question, “How did people put the smell in the candle?” got the students wondering about essential oils. They’d already done some work with scents and lavender plants growing in the school grounds but felt they needed a bigger challenge than simply making lavender bags. Research introduced students to hydrosols – the liquid co-product created when distilling natural materials for essential oils. Sue and the students wanted to know more, so they turned to Venture Taranaki, which runs the Taranaki pilot of the PSP initiative.

PSP funding meant Toko School was able to purchase two stills and all of the associated equipment to make essential oils and hydrosols. A visit to Pihama Lavender introduced the students to steam distillation and uses for lavender oil and hydrosol. Jim Bennett of Still Valley also came on board with his expertise. Jim makes essential oils and hydrosols from native plants like mānuka and exotic plants like hinoki cypress, cedar and pine. He encouraged the students to explore a diverse range of plants for a diverse range of purposes. Toko School’s cleaner also played a role – she challenged the students to find a natural product that would help her clean the classrooms.

The process of steam distillation

Distillation separates a pure liquid from a mixture of liquids. The sequence of events begins with heating, then moves to evaporating, cooling and condensing.

• Water is heated to create steam.
• The steam moves through the plant material.
• Volatile and non-volatile compounds evaporate and rise with the steam.
• The steam (vapour) moves into a condenser – an area cooled by water.
• The steam condenses, returning to its liquid forms.
• The liquids are collected. The essential oil rises to the top or sinks to the bottom and is extracted.
• The remaining water is a hydrosol.

The science behind steam distillation

The science concepts involved with distillation are changes of states of matter and density.

With each distillation, students had first-hand experiences with observing water in its liquid, gaseous and solid forms. In addition to observing the evaporation and condensation processes, the students put the hydrosol in the freezer to separate the oil – this is called drying the oil. The water froze but the oil remained a liquid.

They were also able to compare the distillation process to the water cycle: heat causes water to become vapour, and cooling the vapour (via the condenser) turns the vapour back into a liquid – just like precipitation.

The students learned about density. Many essential oils are less dense than water, so the oil floats on the surface of the hydrosol. Other oils – like cinnamon leaf and clove – are denser, so the oil sinks below the water.

Working as scientists, mathematicians and entrepreneurs

Sue reported that the students learned a lot about measurement – recording temperatures, measuring liquids, comparing inputs to outputs and weighing plant matter.

Their maths has gone through the roof compared to before we started this project, and I think that’s because this is ‘real’ maths, rather than just being on paper.

Sue Fergus, teacher

The students also tested their products to determine their effectiveness as cleaners. They used lemon, lavender, bay laurel, mint, pine, rosemary and hinoki cypress to remove paint, crayon and glue residue from desks. Sue said that lemon and hinoki cypress seem most effective at cleaning. And as is often seen in the world of science, the next steps after discovery and testing are innovation and business start-up. The students hope that their cleaning products will fund a new series of investigations.

Learning impacts

The article Building science capital at Toko School looks at the multiple learning opportunities provided through this project, with video reflections from students, the teacher, the principal and a parent.