QI

For the past few weeks there has been an unusual and appealing smell in the Cottage Garden. Many visitors have asked us why there is a tantalising aroma of toffee wafting around as they walk along the small paths. The answer lies with an elegant tree growing in the corner; Cercidiphyllum japonicum. More commonly known as the Katsura tree, it is a native of Japan and China but has been grown in Britain since 1881. Our tree is now about 30 feet high and has a mature and stately presence with pale, deeply fissured bark and elegant, slightly drooping branches.

The leaves are a rather lovely heart shape, not just a loose heart but a proper one with a sharp ‘v’ indentation at the top and a pointed end. In autumn, they turn a rich buttery yellow and it is the leaves that produce the delicious smell. As they break down, the leaves produce an organic compound called maltol which is precisely the same compound present in toffee and caramel. It’s also found in the bark of larch, pine needles and roasted malt, hence the name, maltol. The food industry use it as a flavour enhancer where it’s known as 636 but the actual molecular formula is C6H6O3. For those of you who like chemistry, there’s an interesting podcast by Oxford University about how the toffee smell can be scientifically identified using gas chromatography and mass spectrometry. For the rest of us, the next time we stroll past a Katsura tree we can now casually inform our companions that the smell is caused by the compound maltol and enjoy their amazement at our brilliance. A little knowledge can go a long way.

The perfect heart-shaped leaf

The perfect heart-shaped leaf

Link to the podcast:
http://podcasts.ox.ac.uk/series/botanic-garden-chemistry-audio-tour.

Helen Champion

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