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The extraction of fragrant organic compounds from flowers

Extract your own flower scented oil
Some fragrant organic compounds in plants are sensitive to heat and so to extract them, we need to consider techniques other than steam distillation or microwaves. One of these is to use an organic solvent. Typically, a solvent like hexane is used to extract the organic compounds from the plant - the mixture made from the solvent extraction is called a concrete. It contains waxes and/or fats as well as the fragrant compounds from the plant - on evaporation of the hexane a semi-solid or solid material is left behind, ideal for making solid perfumes.
Fragrant oils are extracted from the concrete by mixing it with ethanol - evaporation of the ethanol gives a mixture called an absolute, which still contains a small amount of waxes and pigments, but mainly the fragrant low-boiling organic compounds. In this activity, rather than use hexane, we will use olive oil to extract the fragrant compounds from a flower of your choice. Olive oil is made by crushing olives and extracting the oil. The chief components in the oil are esters, called triglycerides, made from long chain fatty acids, principally oleic and linoleic acids. The smell of olive oil is an incredibly complex mixture of low-boiling organic compounds, including (E)-2-hexenal, which contains both alkene and aldehyde groups, and the ester ethyl 2-methylbutanoate.
As olive oil is a mixture of organic compounds, it can act be used to extract fragrant organic compounds from flowers. Flowers are placed into a sealed bottle containing olive oil - cram as much plant material as possible into the bottle and leave it to stand, in a cool, dark place for a couple of days, with occasional shaking. Then strain it and put the liquid in a dark, glass container. Now sniff your extract and describe its aroma, being as descriptive as possible. Is it floral, citrus, oriental, woody, green or mossy? Is it agreeable, exotic, faint, light, overpowering, pleasant, pungent, spicy, subtle or sweet?
As each of us has a unique perception of odour, irrespective of the words we use to describe it, it is likely that we will have different opinions on the same fragrance. Also, odour descriptors are concentration dependent, and we would like you to investigate the effect of varying concentration in this activity. So, as discussed in the accompanying information, add known amounts of olive oil to your extract and at each stage of the dilution, describe the aroma and record your findings. Post your results - it will be interesting to see what flowers you choose, and what effect changing the concentration has on the aroma. It will also be interesting for you to describe what you smell which is not always straightforward!
In this step you will be looking at the extraction of fragrant compounds from flowers through an activity where you will have the opportunity to make your own flower scented oil.
The following ingredients and items will be required:
  • Olive oil or a related oil (such as corn oil or sesame oil)
  • A bunch of flowers
  • Jars – with lids
  • Sieve
  • Measuring spoons/measuring cups.
Ensure that you read through all of the instructions before beginning the experiment to ensure that you understand exactly what will happen at each step.

Step one: select your flowers

Almost all flowers should provide a result, though, for some, it might be a very faint one. Feel free therefore to pick your favourite flower, try one of the ones that we attempted, or maybe even try a herb if flowers aren’t your thing!
Bunch of flowers
We attempted the experiment with three different types of flowers (roses, lilies and carnations) and found that the most intense and obvious smell came from the roses, which happened to be the least pungent at the start of the process; if your flowers don’t smell too floral when you pick them therefore, they should still work quite well.

Step two: pick off the petals

For this step, the important parts of the flower are the petals, so pull those off and use your fingers – or a pestle and mortar – to crush and bruise them before putting them into a jar (or anything that you can stopper to keep airtight).
Make sure that you cram as many flowers into the jar as you can.

Step three: add the oil

You now need to add a known volume of oil (we used extra virgin olive oil, but you could try other less pungent oils such as corn oil or sesame oil) to the petals, in order to be able make up known dilutions and observe how/if the concentration of flower oil changes the pleasantness of the smell.
We recommend a minimum of 50 mL of oil so that you have enough flowery oil to complete the required dilutions.
When you have added enough oil to cover all the petals – remember to accurately make a note of the volume of oil that you have used – stopper the bottle/jar and give it a good shake. You need to make sure that all the petals are covered in oil and that you have shaken the oil-flower mixture until is all properly mixed in together.
flowers in oil

Step four: leave your flower mixture for 24 hours

When your mixture is fully covered in oil, you need to seal the bottle and leave it somewhere dark for 24 hours. After this time, the scents from the flowers should have been fully absorbed by the oil and you should be able to smell something flowery… instead of just olive oil!
Flowers in Oil

Step five: drain your flowers and strain

After 24 hours have passed, you can remove your jars from the dark and take off the lids.
Use a strainer to drain the flower petals, collect the oil in another container, and then use a spoon to press down on the petals against the strainer so that you can collect as much of the flowery scented oil as possible.

Step six: record your results

When you have collected your flowery oil, don’t forget to record what you smell. For example, use words like:
  • Floral
  • Earthy
  • Fresh
  • Light
  • Etc….
In the next step, we will ask you to report back on your findings and observations, but if you want to share your experience of setting up the experiment in this step, we’d love to hear about how you undertook the process.
For your safety it is advised not to eat any part of the flower oil at any stage of the experiment. Dispose of the samples into a general waste bin and do not re-use the oil. Any jars, sieves or measuring instruments used should be washed before being used again in practical cooking.
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