The threat of continued global warming and climate change presents us with dire consequences for the state of the world as we know it. We’re faced with such tragedies as the ice caps melting, the disappearance of species as they struggle to adapt, and of course, the end of the global wine industry. As planet Earth’s temperatures slowly creep up, many of the worlds vineyards and wineries are starting to suffer the consequences.
There are two key things that you need to make wine: some sort of fruit and something to ferment it. Whilst winemaking is incredibly nuanced and technical from a scientific point of view, these two components are the bare minimum present in all fruit wines. The fruit most commonly used in wine is of course the grape, with different varieties of grapes being used to make different wines. Different grapes are found native to different regions of the world, which is part of what has allowed so many different and unique varieties of wine to exist throughout the world. As such, global warming poses a threat to these ecological niches that grape vines are grown in, with the prospect of removing some wine regions off the map entirely.
When the temperature increases, it is only natural for a plant to change its metabolism accordingly – that diverse and flexible metabolism is the very reason most plants can stay in one place their entire lives. Unfortunately, the shift in metabolism caused by a global temperature increase of a degree or two is enough to alter the grapes used for winemaking to the point where it is no longer possible to make wine out of them. As the temperature rises, grapes shift their metabolism to produce more sugar and less organic acids, whilst having a net drop in the pH of the grape and its juices. This can create big problems for the other key player in winemaking and the star of this article: the yeast.
The yeast in wine act to ferment the sugars in the grape to alcohol, as well as various other biological processes that differentiate wine from just an alcoholic grape juice. The increasing sugar content of grapes grown in warmer climates leads yeast to produce more alcohol – often putting wines over the legal limit to be sold, a disastrous prospect for a winery as an entire crop goes to waste. Worse still is that a higher sugar level means an increased osmotic potential, meaning the yeast may not be able to grow at all. This is compounded by the fact that as levels of organic acids and pH dips, the acidity level for yeast growth starts to deviate away from its optimum, meaning the slim hope of yeast growing and fermenting dwindles further.
But this isn’t an article about why we won’t be sat outside enjoying a glass of Pinot Grigio in the summer, or surprising your dinner guests by pairing liver and fava beans with a nice Chianti, this is a success story of the humble yeast living in wine fermentation tanks and casks the world over. If you haven’t noticed, our wines aren’t disappearing. The shelves of the wine aisle of your local supermarket are not at all bare, they’re just as varied as ever. This is because whilst plants are adapting to climate change to survive (completely oblivious about how it affects us), the yeast is also adapting – and it just so happens to be adapting to our benefit.
Researchers in Spain have been thinking long and hard about why our wine industry hasn’t taken the hit from climate change, and their results (which you should take a look at here) are a great example of how microbiology interacts with our everyday lives. The researchers present a thorough and comprehensive analysis of wineries that have observed a noticeable increase in temperature in recent years. They examine several different fermentation methods in wineries that use a variety of different grapes to produce different wines and the results all point to one thing: that the yeast is evolving to cope with the stresses introduced by global warming and climate change.
In the paper, the researchers explain how they isolated yeast strains from 6 different wineries in the Vinos de Madrid region in Spain – an area hit particularly hard by global warming – that use both organic and conventional methods to make their wine. Half of the wineries use ‘spontaneous’ fermentation, which relies on yeast that is residual from previous batches to ferment the wine, whilst the other half add one of several commercially available yeast.
In the study, 1557 strains of yeast were isolated, 713 of which were the expected S. cerevisiae which the researchers narrowed down to 93 different genotypes. Possibly one of the most interesting findings of this study was that of the wineries that added commercially available yeast, one showed no isolates (out of 81) that corresponded with the commercial yeast, and another showed it as one of five isolated genotypes, but it was not responsible for fermentation – meaning in these two wineries, the yeast they were adding was having no effect on the fermentation and the native yeast were doing all the work.
Whilst the data from yeast isolation was interesting in and of itself, the real meat of the paper focuses on how the different genotypes are showing adaptations to the increasing osmotic potential, increasing alcohol levels, and lowering pH. Using microarrays they were able to test the growth of all their yeast genotypes in all the above conditions. The resulting plethora of data shows some interesting trends, with quite a wide range in how the strains respond to different conditions. Amongst them, though, there are some that stand head and shoulders above the commercially available strains in terms of growth.
Growth in adverse conditions isn’t everything, however, so the research goes on to see how well these yeast isolates can actually ferment grape must (the juice and sometimes skins of grapes used in winemaking. White wine being made with just the juice, red with juice and skins, and rosé from juice that has been in contact with the skins for a short while before fermentation). Again a wide range of results came in for the different strains, but within all the data there are a few key gems – or germs – that are able to ferment the wine faster and with less acetic acid production (we like wine, not vinegar) than the commercial strains.
Now, if you’re anything like me, you’re probably sat there thinking this is all well and good, but what about the wine that these supposedly superior yeast are making? Surely, if the wine is made using different genotypes of yeast that have different characteristics, the wine is going to be different? Happily, the researchers in Spain thought this as well, so in a brilliant example of how microbiology impacts the real world, the paper concludes as all good papers should: with a taste test.
The researchers, with a view to potentially use these new isolates as a set of new commercially available yeast strains for the warming climate, performed microvinifications with single isolates to test the wine produced. For this, they used a sterilised must from grapes that had been grown in warmer temperatures to see if the yeast that had (according to their other data) adapted could really measure up when it comes to comparing it to the wines we know and love.
Now before you think to follow in these researchers’ footsteps and go writing grant applications to open a wine tasting section in your lab, the taste tests were carried out by an outside panel of seven judges from the IMIDRA institute – Spain’s Institution for Agriculture, Rural Development, and Food Research. This panel were specially trained in recognising what makes a good wine from its early aromas; many wines require aging to get their full flavour which is beyond the scope of a laboratory setting. This panel tried wines made from the 12 yeast strains predicted to make the best wine, alongside wine made with a control strain from the IMIDRA collection.
The results showed what we’d been hoping to hear since the start of this article: compared to the control strain, the adapted yeast produce a variety of wines which are just as good as the control. The taste test also reaffirms the idea that different yeasts produce different flavours in the wines they ferment – as with the exact same must the 12 different wines were all very different in terms of fruity vs floral flavours, as well as herbal notes and the overall intensity of flavour.
The implications of this result are good news for wine lovers: not only are the yeast in wineries adapting to climate change to keep producing wine for us (and, as a by-product, survive), but specific isolates have been characterised and may well soon be available to wineries worldwide to help them combat climate change too.
Whilst obviously this isn’t the correct attitude for dealing with climate change – tackling the symptoms rather than the cause – at least now we can be slightly reassured that whilst we spend long nights pondering on how best to fix our planet, we’ll be able to do so with a glass of red in hand.
Robert G Millar (University of Warwick)
Categories: Feature Articles