Reference point
Dig under the fallen leaves at the foot of a tree and smell the bottom layer.
Do this before you read on. An entry only works when you have just smelled the thing.
Damp, sweetly rotten, with a mushroom note and a dense layer of earth. Heavy and lasting, clinging to the hand for a long time.
This is the smell of decomposition in progress, and it contains both geosmin and the eight-carbon alcohols of fungi. In other words, it is first rain and straw mushroom added together, in concentrated form.
The top and bottom layers of leaves smell different. Freshly fallen leaves are dry and almost odourless; the deeper you go, the damper and stronger.
How to smell it
Choose the foot of a tree where leaves have lain for a long time. Clear the top layer and take a handful from the bottom where the leaves are dark and matted. Smell at once. Compare with dry leaves from the top.
Why this one is hard
Because the smell is associated with dirt and damp, so the first reaction is to avoid it. It is also easily described as a general forest smell without being taken apart.
Don’t confuse with
This entry
Leaf litter
Earthy family
Leaf litter is fungus and earth added together in concentrated form; straw mushroom is thinner, fishier and has a clear metallic note.
This entry
Leaf litter
Earthy family
Rotting wood is sweeter and less green, because lignin breaks down into different compounds from the cellulose in leaves.
Scientific note
Leaf litter is the product of fungi and bacteria breaking down cellulose and lignin. The process releases 1-octen-3-ol and geosmin, two compounds also found in mushrooms and in soil after rain. So the smell of leaf litter is not the smell of the leaves but of the organisms eating them.
In Vietnamese life
In traditional farming the smell of leaf litter is a sign that the soil is improving. Experienced gardeners judge compost by nose, and this is exactly the smell they look for.