© iStock/W. Blake Gray

The brettanomyces aroma wheel ranges from roses to wet dog

The University of California, Davis, took a major step last week in the official academic overview of wine that smells like excrement.

"Fecal," "wet dog" and "rotting fish" are three descriptors from a new aroma wheel, designed to help describe characteristics imparted by brettanomyces – a yeast which creates two volatile phenols that have distinctive odors: 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG).

The wheel might help explain why some wine smells like sauerkraut or sour milk. But not all the smells on the wheel are bad. There's also rose, cola, Chinese five-spice, mocha and a host of other aromas that have long been used as praise.

And that shows a major philosophical shift at UC Davis, which is the world's foremost university for teaching clean, technical winemaking. While some winemakers in France have argued that brett can impart positive characteristics, UC Davis has been steadfast in leading the argument that brett equals bad. Its professors have always described brett as a "spoilage organism."

Not anymore. "There's no denying that brett is part of many wines' regional character," said UC Davis professor Linda Bisson at a brettanomyces conference.

Bisson and UC Davis colleague Lucy Joseph confirmed what many winemakers have long speculated: that there are many kinds of brett, and some give characteristics that are mostly perceived as positive. Out of 83 strains of brett that UC Davis tested, aroma panelists regarded 17 of them positively.

But Joseph added that none of the positive judgments was universal; it just meant that more panelists liked those aromas than not.

"What you're smelling is not what the person next to you is smelling," she said. "Everything you perceive is based on your genetic makeup and your background."

For example, older Americans compare the compound 4EP to "Band Aids" because bandages once used a similar compound as an antiseptic. In China, different antiseptics were used.

"Chinese tasters thought the 'Band-Aid' character was Chinese 5-spice, and they liked it," explained Joseph.

In addition to adding aromatic complexity, brett also affects mouthfeel – and not always negatively. Brett can create glutamates, which add umami to wine. But it can also make a wine's mouthfeel thinner. Bisson said she would like to research brett's impact on mouthfeel, but so far her organoleptic research has focused on its aroma.

© W. Blake Gray

UC Davis researchers Lucy Joseph and Linda Bisson

Because of its genetic structure, brett evolves to thrive in certain specific environments. This means that certain vineyards may have "positive" strains, as has long been speculated.

However, Bisson cautioned that unlike saccharomyces, brett is unpredictable. The same strain might give floral aromas in one vintage, and sewer-gas aromas the next.

"There's a lot of interest in identifying brett strains that will always be good," she said. "We've almost given up on the search. You think you have one, and then you put it in the next wine and it goes crazy. Bottom line: Brettanomyces cannot be trusted metabolically."

Bisson stressed that if historical winery experience was positive, positive characteristics may recur. However, "it's like having a tiger in your winery, whereas saccharomyces is a cocker spaniel. The tiger might be beautiful, a great pet for 10 years, and then you lose an arm."

That said, Bisson doesn't deny liking brett, which is a novelty for a UC Davis professor.

"615 is one of my favorite strains because it doesn't give you a lot of vinyl characteristics, but it will grow just fine in white wine," she said. "I think it gives you an interesting white wine. I'm in the minority on that one."

The latest research was revealed at a conference where UC Davis had convened a panel of winemakers to talk about brett. Nick Goldschmidt, who worked for both Constellation and Allied Domecq, said brett had spread around the world as wineries bought used barrels.

"I don't remember brett in Australia in the '80s," Goldschmidt said. "But by the '90s, it was everywhere and it was rampant. In Argentina we're just starting to see brett and I don't think people are aware of it."

Goldschmidt is strongly anti-brett, saying, "I don't think brett has a home in wine." But Chris Howell, general manager and winemaker at Cain in Napa Valley, disagrees.

"I'm in love with brett," Howell said. "Brett has a home in my wine. It's always been there.

"Clearly there's two sides to this. The history of a certain smell and the way it's perceived is a question of cultural context. The French recognize brett and were taught it was good."

In his view, that is not the case at UC Davis.

He compared the teaching of information about brettanomyces with learning to make cheese: "[At] a university of food science you learn to make Velveeta. Here at Davis I'm not sure they teach the things that they do at [artisanal] Cowgirl Creamery."