I’ve almost completed reading Nose Dive, the compendium describing molecules that give rise to the diverse smells that we humans experience. Given Harold McGee’s expertise in the chemistry of food, I was not surprised to read plenty of examples in these areas. Today I will highlight just two little bits related to foods I enjoy. I love eating mushrooms (perhaps I have some Hobbit genes) and I love the smell of buttery puff pastry. In homage to chapter titles in Tolkien’s Lord of the Rings, today’s blog post is a play on “Of Herbs and Stewed Rabbit” where chef Samwise Gamgee plays a starring role; there’s also “A Shortcut to Mushrooms” so let’s get to it!
The smell of mushrooms is brought to you by the number eight. Fungi produce a range of eight-carbon volatiles with names such as octanol, octanal, octanol, octenal, octanone, octenone, (note the tiny name differences) and well, you get the idea. I’ll now quote McGee: “The most common and characteristically mushroomy molecule, sometimes called the mushroom alcohol is an octenol. It’s toxic to microbes and repels the slugs that commonly prowl the forest floor.” Since I’m a chemist, let’s get very specific. Technically this is (R)-1-octen-3-ol. This specific name tells you the location of the double bond, the alcohol, and which stereoisomer you’re dealing with.
While this octenol is present in a wide range of mushrooms, specific varieties have specific other smells. The typical white/brown mushroom includes octanone and several benzyl derivatives. The straw mushroom also has octanol, octadienol, and interestingly, limonene, which is often associated with citrusy smells. The shiitake mushroom has octanone, but when it is dried, several sulfurous compounds emerge including the very interesting lenthionine and several other di-, tri-, and tetra-sulfur containing compounds. I’ve been cooking with these varieties for a long time, but about five years ago, I discovered the joy of king oyster mushrooms (the big ones!) which when cooked release sotolon, a lactone associated with the smell of fenugreek or curry. I think of it as “meaty”, far too vague a term for a pro like McGee.
Oddly, I’m not a big fan of truffles. I will eat them when present in a meal, but I don’t think they taste spectacular, nor will I go out of my way to get them. Truffles stay below the surface. They don’t make stalks and caps like other “fruiting” mushrooms that sprout up so that their “seed” can be dispersed. Instead they release strong volatiles, plenty of stinky (to us) sulfides to attract other creatures to dig them up. I’ve heard someone describe the smell as “hog’s heaven” which may explain why pigs are good at digging up truffles.
But let’s get to a smell that I particularly enjoy – the wafting buttery aromas of puff pastry! Puff pastry is brought to you by the numbers ten and four. The standard puff pastry made with margarine releases some ten-carbon aldehydes such as epoxy decenal and decadienal. Other volatiles include nine-carbon nonenal, and two smaller ring structures: strawberry smelling furaneol, and 2-acetyl-1-pyrroline often associated with freshly baked bread and fragrant rices. Buttery puff pastry has all these but also includes four-carbon butyric acid (and its derivatives) and the key molecule diacetyl – which as a chemist I would call butanedione or dioxobutanone.
I also enjoy butter cookies. From Nose Dive, I learned that the Germanic word “cookie” means “little cake”. What do you add to the butter? Sugar, eggs, flour. Now you have something more complex allowing for “more extensive caramelization reactions and browning reactions… [and from egg yolk] long fragmental fat chains and related molecules.” I also enjoy eggs and eat them regularly. But that’s another story!
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