Have we domesticated yeast? Yes.

Common sense says that winemakers – and beer brewers, and bread bakers – were developing specialized Saccharomyces cerevisiae yeasts a good long while before Red Star marketed its first dried and packaged commercial product to the industry in 1965. Winemakers weren’t inoculating ferments with an aluminum foil packet they bought at the store, but that doesn’t mean they weren’t inoculating, maybe with a little bit of an already-active ferment, maybe just by having a conducive winery environment where the right kinds of yeast were happy to make a home. Either way, the yeast you’d find in any given winery or brewery weren’t the same as the yeast you’d pick up off the street, or the same as what you’d find in the next alcoholic beverage factory down the road.

Plenty of evidence, old and new, supports that story. But did those yeast become different simply because they were isolated from each other, like Darwin’s famous Galapagos finches? Or did they change because they became domesticated, because brewers and winemakers cultivated and selected them? In other words, what kind of difference did the humans make to the yeasts’ evolution?

The theory basically goes like this. If yeast populations developed in different ways just because they were physically separated, then their genomes should look like what you expect from “wild” yeast. If humans domesticated them, they should be less genetically fit, because they’ve grown accustomed to being specially cared for and protected by humans and have lost some of their capacity to live on their own.

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The neurophysiological shape of wine expertise (and why reports that somms are Alzheimer’s-resistant are wrong)

Even if you think of your brain as a muscle, you probably don’t think about it literally bulking up as a result of exercise. It does, at least in some cases. Master sommeliers – professionals who we assume (and sure hope) have intensively developed senses of smell – have more white matter in regions of the brain associated with olfaction, according to new research (open-access) comparing images of master somm’s brains with those of randomly wine inexpert university students. Very similar patterns of brain-buffness have been found in the heads of professional perfumers.

There’s a funny paradox at play here. On the one hand, smell is probably the least understood of the senses – at least if we’re only counting the canonical ones. On the other, in part because it’s so little understood, smell is a favorite subject for this kind of study. You might suspect that smell is also useful for being simple and isolated from other elements of mental function. It’s not.

One reason for being interested in the brain’s anatomy of smell is to test the limits of neuroplasticity – how much our brains can change after we become adults. (How much can it change? A lot more than previous models of human development allowed.) At least in the United States, most wine experts will have learned their craft as adults. Another reason for smell-focused research is that olfactory regions are among the first to deteriorate in Alzheimer’s and Parkinson’s, to the extent that smell impairment is being considered an early warning sign of those diseases. That link is especially interesting in light of the mountain of scientific and lay-person evidence linking smell with memory.

I’m still waiting for the study investigating whether well-trained oenophiles have better memories or are less prone to Alzheimer’s. Which, contrary to reports by writers who actually earn salaries for their work, is not what this study did. This is observational research about neuroplasticity and developing expertise, about the capacity of the adult brain to change shape with training. No one investigated rates of Alzheimer’s amongst aging sommeliers. No one gave them memory tests. Certainly no one sat around and watched the somms who took part in this study into their retirement years to check up on their mental acuity. Even if they had, too few sommeliers were involved to make any kind of statistically significant judgment even about a disease that the US National Institute on Aging calls the sixth leading cause of death in the United States.

We can say that the effects of intensive sensory training are apparent on an MRI. We can’t say that becoming an expert wine-sniffer prevents Alzheimer’s. Not yet.

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.