If there’s been a theme to the wine microbiology research of the past few years, it’s been microbial communities. Don’t just study one yeast or bacteria at once; look at an environment’s microbial population. And if there’s been a supporting theme, it’s been non-Saccharomyces yeast. Don’t just look at Saccharomyces cerevisiae; pay attention to at least some of the other, marginalized members of the microbial community, and ask what they can do for you.
Those two themes are obviously related. Studying microbial communities means noticing all of the auxiliary players in the environment. Noticing those players usually leads to asking what they’re doing and then to asking how you can exploit them. In another way, though, those two themes don’t overlap half often enough. Plenty of studies of non-Saccharomyces organisms keep on plodding on in the old microbiology tradition of poking and prodding at one or a few species as though they’ll work alone outside the lab.
Very forgivable in one sense. When we don’t know much about an organism in the first place, sussing out its individual characteristics before querying how it behaves in mixed company doesn’t seem unreasonable. It’s also fair to say that plenty of winemaking involves making an effort to kill all existing microbes before inoculating one selected S. cerevisiae strain that’s supposed to work alone. Then again, single-microbe studies remind me of studies of individual primates held in solitary captivity, which are not only deeply unethical but not very useful. What primate, humans included, is going to behave normally when held in solitary confinement? I’m not claiming that solitary microbe studies are unethical, or that they do harm to the microbes involved, but we have plenty of evidence that microbes are social.* Data from solitary confinement studies is limited.
So a new study on Schizosaccharomyces pombe is heading in an interesting direction, but yields data with some limitations for winemaking.
Is S. pombe a spoilage organism? That’s like asking whether dandelions are weeds: yes, in the lawns of a golf course; no, when you’re growing them for salad greens. S. pombe produces unpleasant quantities of acetic acid. It also efficiently (and even completely) metabolizes malic acid. Scott Labs sells S. pombe “teabags” that can be dropped into overly acidic tanks or barrels and then fished back out again, after malic acid has been degraded but before volatile acidity gets out of hand. New research (open-access article) has considered whether some S. pombe strains, carefully selected for low acetic acid production, might be suitable as primary fermentation organisms to be used instead of S. cerevisiae rather than afterwards. The team was able to find several low acetic-producers, able to ferment a must to dryness (albeit they tested final alcohol concentrations in the 12-12.5% range), and still able to simultaneously metabolize malic acid. Their perfunctory sensory testing, however, pretty much only judged for major faults: acidity, reduction, acceptable aroma. So when the researchers conclude that these strains might be a good option for high-acidity musts instead of malolactic fermentation, they’ve yet to account for whether that solution produces a delicious product or merely an acceptable one. Still, these strains might be incredibly useful in combination, or when a vat of something undrinkably acidic needs to be made inoffensive enough to be blended away into something else. But how do these microbes behave in company, when asked to cooperate on the job of making a drinkable wine?
I hope that this project steps forward in two directions. One: better sensory analysis. Two: what happens when S. pombe and S. cerevisiae (and perhaps some other bugs) are asked to play together.
*The Foster Lab at Oxford is up to interesting research on cooperation between microbes and other species. Here’s another (albeit dated; 2007) excellent resource on microbial sociability, from Annual Reviews in Ecology, Evolution, and Systematics. Unfortunately, it’s also behind an academic publisher’s paywall.