Wednesday, September 2, 2009

Psychedelic Citrus

Above and top: spheres of citrus oil trapped
amongst the cells in orange peel x100

Vertical section through an oil gland in orange peel.
In the intact gland oil accumulates in the central cavity
and leaks out onto the surface of the fruit via a minute pore. Polarised light. x40
The shiny flash-shaped patches in the surface of the orange peel,above the white pith, are the oil glands full of intensely fragrant oil.

Pleasure from eating comes from a combination of the taste and smell of food , and when it comes to oranges these two factors are subtly different but complementary. The distinctive taste comes from the soft acidic flesh, which only has a relatively faint aroma compared with the intensely fragrant peel. To see what I mean sniff an orange segment, then compare its scent with the rind by holding a small piece of peel under your nose, surface towards you and squeezing the peel hard. You’ll feel the citrus oils that are squirted from the flesh against your top lip and will experience a very strong citrus smell. The citrus oils are concentrated in hundreds of microscopic glands under those tiny dimples that cover the orange skin. This lunchtime I cut a thin vertical sliver through the peel of my orange and took a look at it under polarised light, which creates the psychedelic interference colours that you can see in the top three images. The central cavity of the oil gland is where the citrus oil accumulates as the fruit grows, but it leaked away when I cut the sliver of peel with a razor blade. The top two pictures show the residual citrus oil droplets that were trapped in the peel sliver, looking like those globules in 1960s lava lamps. We throw the fragrant but inedible orange peel away, but citrus oils have many commercial applications, in food flavourings and in the fragrance industry. In nature, their role is probably as a defence against insects that might otherwise burrow into the fruit. You can read more about citrus oils at

1 comment:

  1. Another fascinating illustrated post Phil. I had always assumed that the smell came from the juice but now I know better.


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