GMO yeast in wine and how to find them

The vast majority of wine does not involve genetically modified organisms (GMOs). Let me repeat, the vast majority of wine does not involve GMOs. On to the rest of the story:

Whether wine contains genetically modified organisms (GMOs) is a question I’m asked often. In general, the answer is no. Genetically modified grapevines aren’t being used for commercial winemaking (though not for want of trying). Two genetically modified wine yeasts have crossed the commercial production threshold, but not worldwide. One, the un-charismatically named ECMo01, available only in the United States and Canada, has been engineered to produce an enzyme that degrades urea. That’s a useful property because urea in wine can become ethyl carbamate, which the World Health Organization thinks is probably carcinogenic enough to be worried about it.

The other, ML01 (which rolls off the tongue much more easily), is legal in the US and Canada as well as Moldova, and seems to have won more traction (though not, I dare say, because it’s available in Moldova). ML01 includes genes for two non-Saccharomyces cerevisiae proteins: a malate permease from fellow yeast Schizosaccharomyces pombe, and a malolactic gene from the lactic acid bacteria Oenococcus oeni. Together, those molecules allow ML01 to import malic acid into the cell and convert it into lactic acid, granting ML01 the rather magical ability to perform both alcoholic fermentation and malolactic fermentation simultaneously, all by itself. In addition to speed and convenience, this one-stop fermentation is advertised as a route to fewer wine headaches. Lactic acid bacteria can produce biogenic amines, which can produce headaches and other unpleasantries in sensitive people (I’m one of them); eliminating the need for those bacteria should eliminate the biogenic amines and those symptoms.

For reasons which are probably obvious, North American wineries using these GM yeasts don’t exactly go shouting that news from the rooftops, fewer headaches or not.

What if you wanted to identify whether or not any given wine was made with a genetically modified yeast? You’d go looking for the modified gene, right? This isn’t as simple as it sounds, and not just because genes are very small. The genes that distinguish ML01 and ECMo01 are also found in other common wine microorganisms; detecting ML01, for example, means ensuring that you’re not just detecting the presence of perfectly normal malolactic bacteria.

The authors of a recent paper in the International Journal of Food Microbiology handled these problems with a conceptually simple solution to identify ML01 in mixed microbial company. They used PCR – the polymerase chain reaction, or the standard means of “looking” for genes that constitutes the bread and butter of virtually every molecular biology lab these days. PCR amplifies a very specific DNA sequence, determined by “primers” that line up with the genetic sequence you’re looking for, so that even a tiny amount of that genetic sequence in a sample can be detected. By choosing those primers to line up with the joints at either end of the signature ML01 genes – the scars left over from its engineering procedure, essentially – they could target the engineered yeast to the exclusion of both O. oeni and unmodified S. cerevisiae. By using quantitative PCR, which adds some fancy fluorescent chemistry to the basic PCR process to provide a rough idea of how much of that specific genetic sequence is in a sample, they could distinguish between large quantities of ML01 indicating that it was used for primary fermentation versus small quantities suggesting accidental contamination

The goal, in this paper, was to offer a means of establishing whether GM yeasts are being used illicitly in countries where they’re illegal as well as a test against ML01 contamination in factories where it might be produced near non-GM strains.

That’s how to find GM yeast in wine if you’re a biologist. If you’re not, you’re left with less precise methods. One: exclude wine from outside North America and Moldova. Two: exclude organic wine and wine from companies which expressly declare themselves non-GM-users. Three: recognize that the general ethos of a winery probably gives you a good idea of how likely they are – or aren’t – likely to use ECMo01 or ML01. Four: invest in a PCR machine.

*See, for example, this Australian report from 2003, or this Cornell proposal from 1996, along with numerous research projects investigating the concept.

 

Carbonation and the pain of Champagne

Sparkling wine – or beer, or soda, or seltzer* – triggers an unmistakable set of sensations, addictive or repellent depending on your predilection. But is that sensation a taste? A physical sensation? Something else? Probably some combination of the above, though figuring all of that out is trickier than you might imagine.

First, the bubbles in sparkling wine are carbon dioxide, either the product of yeast fermenting a last little bit of sugar in the bottle or mechanical carbonation with a tank of pressurized gas. Carbon dioxide plus water makes carbonic acid: CO2 + H2O ⇌ H2CO3 . Acids, by definition, are molecules with hydrogens which can and do pop on and off when dissolved in water. If the hydrogens tend to disassociate themselves easily, you’re dealing with a strong acid (e.g. hydrochloric or sulfuric) best used for cleaning glassware or dissolving an inconvenient corpse. If only a small number of hydrogens hop off at any one time, you’re dealing with a weak acid. Carbonic acid, needless to say, is a weak acid, or else seltzer water would be an industrial solvent rather than a cocktail mixer. Chemists were associating the perception of sourness with those free hydrogen ions back at the turn of the twentieth century, but they’re not sufficient to explain sourness alone, and twenty-first century chemists are still trying to work out the remainder. The ongoing search for a complete explanation of sourness is one of those excellent examples of how very simple daily phenomena can end up being unexpectedly complicated when scientists try to explain them in terms of chemistry and biology.

Second, the bubbles in sparkling wine are mechanical stimulation. If you stick your hand into a glass of sparkling water, you’ll feel the “prickle” of bubbles bursting along your skin, and your tongue and the interior of your mouth receives the same sensation. That’s not surprising.

A third component of how we sense carbonation is surprising, or at least it’s surprising to me as a carbonated beverage-lover. Carbonation appears to trigger nociceptors, the specialized receptors we have for sensing pain. Carbonation is, physiologically speaking, irritating.

Maybe it’s not surprising to find that Champagne belongs on the list of painful foods along with super-spicy cuisines and overly hot tea. Or, rather, a goodly number of people seem to find Champagne painful for numerous different reasons. Drinking Champagne and enjoying it is a social skill, but everyone seems to know at least someone who really doesn’t like the stuff. Some are folks who don’t enjoy wine or alcoholic beverages at all, and some are surely like me in liking sparkling wine but having mainstream Champagne sullied by thoughts of what other, more interesting wines could have been purchased for the same $40. Perhaps some of them are also troubled by unusually high sensitivity to the negative sides of carbonation. A recent study of how consumers perceive small differences in degree of sparkling wine carbonation attests that individual tasters have different thresholds for feeling – and maybe feeling discomfort from – carbonation. Occam’s razor still says that “Champagne”**-haters are more likely suffering from a combination of low-quality bubbly, ill-advisedly sweet food pairings, and excess consumption. But heck; the simplest answer isn’t always the correct one. Just look at the sensation of sparkling.

As for me, I’m strongly in the pro-carbonation camp. I also eat 100% unsweetened chocolate straight-up, take strong tea and coffee black, and eat bitter greens for breakfast all of which, I’m told, are rather painful suggestions to many people. Perhaps these statements are not unrelated?

 

For more on sparkling wine physics: http://palatepress.com/2012/12/wine/champagne-physics-or-what-science-can-tell-you-about-drinking-your-bubbly/

For more on Nobel prize-winning sparkling wine microbiology: http://palatepress.com/2012/11/wine/yeast-martyrdom-toasty-flavors-in-your-sparkling/ and http://palatepress.com/2016/10/wine/nobel-winning-research-also-explains-the-taste-of-champagne/

 

*Or carbonated foods. This soup? Fermenting kimchi? Pop rocks?

**In quotes only because people who object to “Champagne” may be reacting to negative experiences of other non-Champagne sparkling wines and I’m not interested in picking a fight with the CIVC.

When microbiology is a data problem: Putting science together to make better pictures of yeast

Short: A Portuguese-based group is suggesting that winemakers could have more useful information about choosing a yeast strain if scientists did a better job of putting together data from different kinds of experiments.

Longer:

Scientific research generates a lot of different shapes and sizes of data. How does anyone make it work together?

Contemporary scientific research has a lot of big challenges, but here are three: funding, replicability, and integration. Funding is a great big gory topic for another day.

Replicability has seen a lot of attention in recent science news: scientists across disciplines have been reporting difficulty duplicating their colleagues’ results when they try to repeat the same experiments. This is worrisome. (Most) science is supposed to be about making observations about the world that remain the same independent of who is making the observations. Two careful people should be able to do the same experiment in two different places and obtain the same results. Well-trained scientists, however, are finding themselves unable to replicate the results described in scientific papers, and the community isn’t sure what to do about it.

Integration – how to fit together large amounts of lots of different kinds of data – looks like a separate kind of problem. Scientists (microbiologists, biochemists, systems biologists, geneticists, physicists…) study a thing – yeast, say – in many, many different ways. They generate data in many different shapes and sizes, using all manner of different kinds of instruments to make numbers that don’t just tidily line up with each other. But, at least in theory, all of those data are about the same thing – the same yeast – and so finding ways to integrate data from different kinds of experiments should massively improve our understanding of how yeast works as a whole.

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