The Science of Sake Aromas

One of the most appealing things about wine is its range of beautiful and complex aromas. Many echo the scents of our favorite fruits, vegetables, flowers and herbs. But they can sometimes be off-putting, too. You know, cat piss, nail polish, gasoline—things that no one really wants to inhale with their dinner, yet which can somehow please our noses and palates when they are part of a larger mix of aroma and food combinations.

Sake too, has its share of volatile aromas ranging from the fruity to the umami-laden, which have increased in number and complexity with the advent of ginjo sake and modern yeasts. I learned more about the science behind fragrances in a fascinating book, Nose Dive: A Field Guide to the World’s Smells, by the science and food writer Harold McGee.

McGee’s quest to map the aromas of the world began with a question: Why do certain aromas seem to echo throughout nature? “If oysters can smell like cucumbers, then which was the first to carry that particular molecule? And did something else carry it before either of them?” The sake lover might likewise ask, why does a Kameizumi junmai ginjo brewed with Cel-24 yeast burst with mouth-puckering green apple, melon and floral aromas and tastes, or a  Tedorigawa yamahai junmai with notes of yogurt and toasted cashews?

 Of course, seishu (清酒) or “clear sake,” as it is defined by Japanese liquor laws, does not contain any fruit, flowers, dairy products of nuts. Instead, these aromas emerge during the fermentation process, carried by aromatic volatiles that are close parallels to the families of molecules that are assembled in plant, animal or fungal metabolism.  

 The book’s most interesting revelation about volatile aromas is that the most basic of them are billions of years old, pre-dating the existence of earth, and the fruits of the natural world that we associate them with. They originated with the Big Bang, that massive explosion of energy that occurred nearly 14 billion years ago, which created matter out of non-matter. Of the 200 or so “interstellar” molecules that scientists have so far identified, only a couple dozen have aromas that we can discern. These “primordial” volatile molecules are made up of simple carbon chains, and can be grouped into different families: aldehydes, ketones, alcohol, fatty acid and esters, each of which contribute unique aromas, ranging from cooked eggs and vinegar to green apple, cocoa, nuts, or unflavored vodka.

“Lighter fluid or stove fuel, scorched oil, a vinegar dressing, a deviled egg, a just-unwrapped cheese, a sip of wine or rum: all offer distant echoes of the early cosmos, sensible traces of the inherent, relentless creativity with which matter explores its own possibilities,” McGee writes.

I checked in with Brandon Doughan, head brewer at Brooklyn Kura, because I know he’s both a trained biochemist and a talented brewer. I wanted to see what his thoughts on sake aromas are. “I am constantly in awe of the sake fermentation process,” he says. “That you can take rice, which arguably is odorless, combine it with different strains of koji and yeast, at different fermentation temperatures and get such widely different aromas is mind-blowing to me.” Noting that he is “in a perpetual exploring and learning state,” Brandon says rather than changing up koji-kin, he’s more interested right now in playing with combining several different yeasts in one brew. He’ll creates separate starters with each yeast then combine and ferment them, or create separate moromi (main mashes) using different yeasts, then press and then blend them together.

“Things can get complicated fairly quickly by adding variables to a ferment (no kidding; my mind is already spinning thinking of the possible permutations of all this combining) but it is exciting when you stumble across something unique,” Brandon adds. “It’s also interesting that different yeasts seem to have their own personalities. Some are strong fermenters, some need to be babied, some will only give certain aromas if the temperature and koji enzyme balance is kept very exact.” This gives you an idea of the lifetime of brewing it would take to master such nuances.

But back to Harold McGee and his book. As eons passed following the birth of those first, primordial, aromatic molecules, earth’s life forms grew in complexity. Photosynthesis, which evolved about three billion years ago, ushered in the miracle of plant life, which draws its energy from the sun. Biological life on earth evolved from single-celled organisms to multi-celled aquatic and then land creatures. As life grew in complexity, new volatile aromas were released into the air.

But even the most complex of the volatile aromas—the terpenes of cannabis, the phenols of ale or the aldehydes of perfumes—are still quite simple in structure, between two and four carbon atoms long; heavier carbon chains would not be able to achieve lift-off, making it impossible for them to waft through the air and into our noses!

One of the subsets of volatile molecules most relevant to sake lovers are esters, because they are the largest and most important group among fruity-smelling volatiles. Esters are the result of the union between two short atom chains, an alcohol chain and an acid chain. They’re responsible for a lot of pleasing ginjo aromas: banana, strawberry, citrus, mango, passion fruit, pear and papaya. One ester subset, lactones, can produce coconut, peach and also dairy notes of cream and butter. A second subset, furanones, are responsible for pineapple and caramel.

In sake, we also hear a lot about the umami-rich qualities that amino acids (shoyu, cereal, miso notes, for example) bring to richer, sometimes even gamey, kimoto and yamahai styles of sake. In the world of volatile aromas, these come from a different class of molecules, the carbon chains that are associated with animal proteins.

The third important class of volatile molecules when it comes to sake are those produced by the fungus kingdom, which includes the mold aspergillus oryzae and sake yeasts, both of which are so key to sake fermentation. In addition to being crucial to the creation of soil, McGee writes, “fungi are virtuosic chemists, whose creations please, intoxicate, and cure us,” noting that alcohol, LSD, and penicillin are all fungus-derived products.

This book fits into my fascination with the microbiome and the huge but invisible role that microbial life plays in our lives and on all life on land and in the deep sea. For more on their importance in human and soil health I recommend science writer Ed Yong’s I Contain Multitudes and David R. Montgomery’s The Hidden Half of Nature. We humans and our favorite alcoholic beverages are shaped and controlled by key microbes, and we both emit our own special volatile aromatics.

Here’s a cool example from Nose Dive of how our microbiome serves to intensify the pleasure of eating and drinking: Certain microbes in our mouths have the ability, like a key fitting into a lock, of liberating certain volatiles molecules that would otherwise be unavailable to us.

It was the French wine chemist Émile Peynaud who noticed how our noses can pick up the Sauvignon Blanc wine grape’s “very specific smell floral, musky, smoky, with a slight raw herbaceousness suggesting bruised leaves,” McGee writes—but only very weakly. The juice of the grape too, Peynaud noted, has relatively little smell. But 20 to 30 seconds after swallowing the juice, “you suddenly experience a powerful aromatic rush at the back of the mouth as the Sauvignon fragrance returns.” What makes this intense echo effect possible?

In 2008, scientists at the Swiss flavor and fragrance company Firmenich (artificially manufacturing flavor and fragrance is a big business!) figured out the science behind this phenomenon: Holding Sauvignon Blanc juice in your mouth does release those smells Peynaud described, which are created by a six-carbon version of smaller sulfur molecules found in cat-pee. And it is microbes that provide the key to unlock this aromatic volatile in the mouth. This same mechanism also allows us to taste the flavors of green bell pepper and onion powder.

This post is getting long, but I’ll just mention one last thing about the mechanism of tasting sake or any other food or drink. It’s fascinating that the smells and taste of our world are all based on the earliest and tiniest building blocks of life, blocks that predate even earth itself. But equally fascinating is the indispensable role that our brains play in interpreting them. Smells, tastes and flavors are all products of our brain, McGee notes. And our brain is not just a passive recorder of incoming data: it “actively creates smells and taste and flavors by filling out those reports with many other kinds of available information, especially information from its database of past experiences.

This truth is one that Proust intuited with his famous madeleine: taste and aroma sensations—whether from a sake brewed using malolactic fermentation or a madeleine, can be the trigger for a rush of powerful memories and emotions, unlocking a door to our own past.

If you like this blog post, click here to sign up to receive future posts in your mailbox!