Human intervention increases yeast biodiversity? Sort of.

A new article in PLOS ONE (which, being open-access, you can read for yourself) headlines with the promising title “Yeast Biodiversity in Vineyard Environments is Increased by Human Intervention.” Unfortunately, the paper probably doesn’t mean what you’re thinking it means.

The authors collected yeast from vineyards across the Azores, an archipelago off the shore of Portugal where, following the usual story, viticulture arrived with European settlers in the 15th century. The article says that more than 85% of vineyard acreage has recently been abandoned in the course of “social and economic change,” creating an array of cultivated and abandoned vineyards geographically isolated from each other and the rest of the world. This sounds like a fantastic research setting, even if you don’t take into account “doing fieldwork” meaning “walking around vineyards in the Azores.”*

As advertised, the authors took samples across these vineyards and found that the cultivated vineyards harbor higher numbers of individually distinct yeast strains than vineyards that have been abandoned for at least five years. What that means, however, is a little tricky.

The scientists picked bunches of grapes directly from vines into sterile plastic bags, crushed the grapes inside those bags, and then spread the juice onto what microbiologists call rich media** in Petri dishes, and then used DNA sequencing to identify (some of the) yeast colonies that grew on the surface of the media (jello, essentially) in the dishes. So:

  • We’re only looking at yeast on grapes, not in the soil or “in the environment” more generally. A different, maybe more interesting picture of “vineyard diversity” might have come from microbes in the soil.
  • We’re only looking at yeast willing to grow into visible colonies in two days under standard lab conditions (and the scientists also only sequenced some of those colonies). Most yeast will be happy to oblige, but not all yeast cells present in the environment will become visible colonies in dishes (and some will grow slowly. A lot of microbiology research these days side-steps that problem by sequencing all of the DNA present in a sample, but that option is, as one might expect, more expensive and more difficult. These techniques don’t mean that the older grow-in-a-dish options are completely not-useful or wholly obsolete, but they’re a good reminder that growth-in-a-dish always gives us a limited picture of a microbial world.
  • We’re not comparing cultivated vineyards with the untrammelled wilderness. We’re comparing cultivated vineyards with previously cultivated vineyards that are no longer being maintained as such. We don’t actually know anything about environments on this island where human cultivation hasn’t happened.

The authors are right: this study works against the idea that human activity always decreases ecosystem diversity. And it does say something interesting: that (at least in this setting), human maintenance increases the number of yeast species on grapes. This study continues to support the hypothesis that humans and/or their equipment are a source of vineyard yeast. It’s a good reminder, too, that “human intervention” (you could also say “humans living and working as part of the environment,” if you felt like being contrary) isn’t necessarily detrimental. Though it’s also worth remembering that increased biodiversity isn’t necessarily either “natural” or universally beneficial, either. If humans intervened to increase species diversity in the Arctic tundra, would that be a good thing? We might work on finding better ways of listening to environments telling us how they’re feeling. In the meantime, I suppose that this is a start. 


*Part of it is also a UNESCO World Heritage site.

**Rich media = lots of nutrients = easy for most yeast to grow.

The objectivity of subjectivity in wine tasting and UC Davis’s first enology professor

Dr. Steve Shapin is a professor of the history of science at Harvard and a distinguished senior scholar. He’s also an oenophile. Sometimes these things mix, especially when he’s talking about the difference between subjectivity and objectivity. When they do, I end up with five or six emails from friends and colleagues saying, “Hey, Erika, did you see that wine article in [title of the most eminent academic journal in our field]?”

Yes, I did. And since you can’t, unless you belong to an institution that subscribes to Social Studies of Science, here are Dr. Shapin’s main points:

  • Maynard Amerine and the sensory science movement he engineered as the University of California Davis’s first enology professor were “objectivity engines” that turned uselessly soft subjective experience into reliably hard objective knowledge…
  • BECAUSE (at least in part) Amerine needed tools to help producers improve California’s wine quality, and then needed to be able to convince Francophilic American wine consumers that Californian wine was really, objectively, good wine
  • BUT: subjective and objective assessments are essentially dependent on each other, with the “objective” tools the product of documenting one or a group of individuals’ subjective experiences and asserting that everyone should use their terms…
  • AND: what counts as objective and subjective in any context depends on that context, and a bunch of what counts in the 20th c. Amerine/Davis tradition as Objective Wine Sensory Information would be called a subjective judgment somewhere else.

In short, the capitalist (and egos or, if you’d rather, a man with a dream) had a lot to do with why we’re now all talking about raspberry and asparagus flavors instead of about elegance and finesse. Alright: some of us still use elegance and finesse, but Amerine wouldn’t have approved. Shapin, who spent time in the archive of Amerine’s papers, says that Amerine also didn’t approve of “flinty,” “petrol,” or “terroir;” the first two were characteristics he said he’d never found in wine, and the third was just the result of dirty winemaking. With very few exceptions, his terms didn’t refer to specific chemical compounds in wine (those came later, and Amerine was skeptical about explaining sensory impressions in terms of specific chemicals); they were about choosing terms that had some kind of “real” referent in sensory experience. According to his system, you could find raspberry in wine, but you couldn’t find elegance.

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Nutrition labels for wine bottles: A good rationale, and a better one

Talking about nutrition labeling for wine is useful. But a new study (open-access article) assessing consumers’ interest in nutrition info on wine bottles limits its usefulness from the first sentence. The introduction begins, “Alcohol misuse…” Yes, alcohol is misused. But framing research in a way that says that alcohol is important because it is misused colors everything that follows: alcohol is going to be treated as a social evil; alcohol is going to be treated as a drug; alcohol is going to be treated as something that needs to be controlled and restrained; wine is going to be treated as alcohol. Those assumptions are especially out of place when we’re talking about nutrition labels, things usually used for food.

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