have the scientists done for us?
Advances in wine science over the last 20 years
article was originally written for the 100th edition of the Circle
of Wine Writers’ Update
a scientist, but—as Andrew Jefford so nicely put a few years back
when reviewing my wine science book—I’m not a scientific
fundamentalist. Science is just one of the lenses we can use to
examine wine with, and there’s still a great deal about wine that
science can’t really explain. Most of the world’s great wines
are not made by technicians, but by artisanal wine growers, working
empirically. They observe; they experiment; they understand.
still don’t have a good scientific explanation for why the wines
of, say, Domaine de La Romanée Conti’s Grand Cru vineyard sites
in Vosne-Romanée are so fabulous, while a few hundred yards away,
very similar-looking vineyards produce rather ordinary wine.
category of natural wine also creates problems for wine scientists:
all that we know about wine science suggests that wines made without
any addition of sulfur dioxide should be awful, but natural wines
are frequently thrilling. It’s a bit of a mystery.
what about biodynamics? Some of the world’s smartest wine domains
have improved their wine quality by farming this way, but science is
at a bit of a loss to explain how some of biodynamie’s
anti-scientific practices could be having much effect.
science is just one way of seeing the world, it is incredibly
powerful, if, as a tool for understanding, it is used effectively.
Some of the problems wine science has run into have been down to the
fact that the wrong sorts of questions have been asked by those who
don’t really understand interesting wine. In the right
hands—those of a curious, committed winegrower—science has the
power to help people make more interesting wines more consistently.
Sadly, it has largely been used to make cheap wine more consistent,
and more cheaply.
this article I’m going to pick some of the recent advances in wine
science, and try to explain why I think they have been so
significant. I’ll also be casting an eye to the future, to suggest
ways in which wine science might progress.
Post-bottling wine chemistry, and wine bottle closures
sounds really dull, doesn’t it? But it’s probably the single
biggest contributor to improvements in wine quality that have taken
place over recent decades.
years ago cork had pretty much a monopoly position as the wine
bottle closure. And cork was doing a really bad job. In particular,
the Australians were getting fed up with the quality of corks they
were being sold. Depending on who you talk to, up to 10% of their
wines were being spoiled by cork taint and/or early oxidation
because of problems with corks. The search for an alternative became
a serious one.
plastic corks were tried. The first-generation synthetics were
injection-moulded plugs that were much less effective than their
modern counterparts. Despite their drawbacks (one of which was that
they were quite hard to remove from the bottle), they achieved
limited success from the mid-1990s onwards. The other main contender
was the screwcap. Screwcaps had been tried in Australia in the
mid-1970s, but had failed to win over consumers.
made their comeback in 1999, when Orlando decided to bottle a
high-end Riesling under both cork and screwcap. The screwcapped
bottles outsold the cork sealed ones by far. Then in 2000, a bunch
of Clare Valley producers banded together and bottled their
Rieslings under screwcap, accompanying their launch with a big media
splash. New Zealand producers also rushed to bottle their fresh
Sauvignon Blancs under this new closure.
what of the science of closures? At this stage, everyone pretty much
assumed that the job of the closure was to seal the bottle, to stop
air coming in and wine getting out. What they didn’t realize was
the critical role played by the closure in allowing a very small
amount of oxygen transmission, and the potential impact this would
have on the wine. It was a pioneering study by the Australian Wine
Research Institute (AWRI), beginning in 1999, that opened
everyone’s eyes to the fascinations of post-bottling wine
study involved the same wine – a 1999 Clare Valley unoaked
Semillon made by Leasingham’s Kerri Thompson – sealed with 14
different closures. These bottles were sampled at regular intervals
and subjected to both chemical and sensory analysis. The long and
short of it is that the synthetic corks used in the AWRI study
allowed too much oxygen transmission, resulting in premature ageing
and then oxidation of the wine.
natural corks were better, but varied quite a bit and tainted some
of the wines. The technical corks were better than the natural corks
in terms of oxygen transmission – they were consistent and kept
the wines a bit fresher – but they too suffered from taint issues.
The screwcap performed best in terms of keeping the wine freshest
and most youthful, but allowed so little oxygen transmission that a
subtle reductive flint/rubber note appeared in the wines.
should be pointed out that with a screwcap, the oxygen transmission
rate is determined by the liner, and two are commonly used for
wines, with rather different properties. The trial here used one
with a metal layer in it – as in fact almost all the screwcaps
used in Australia and New Zealand have. This allows very little
oxygen transmission at all. The Saranex-only liner, the other one
commonly used, allows a bit more: less than a typical synthetic cork
but a bit more than a typical natural cork.
conclusion from the trial is that winemaking extends beyond
bottling. The oxygen transmission rate of the closure that you
choose will affect the sensory properties of your wine after
bottling. It is just not possible to freeze a wine in time by using
a hermetic (totally air-tight) seal such as sealing a wine in a
glass ampoule. The wine will always change after bottling, and the
key issue is to choose a closure with the oxygen transmission rate
that suits the wine (if you know the intended point of consumption).
of the approximately 18.3 billion bottles sealed each year,
alternative closures account for some 5.7 billion units. As a result
of the emergence of alternative closures, winemakers are now aware
of the importance of oxygen transmission through the closure, the
impact of oxygen at bottling, and the processes that occur
post-bottling in terms of wine chemistry. And cork manufacturers are
now trying hard to reduce the rates of taint in their products.
The science of sustainable viticulture
is a biggie. Think back 20 years. Most vineyards were clean
cultivated with herbicides, kept verdant green with chemical
fertilizers, and protected from disease by systemic fungicides. They
looked lovely. The concept behind this ‘old viticulture’ was to
see the vine – the crop plant – as the focus of all the
attention, with the soil viewed merely as an inert medium to supply
the necessary nutrients and water for vine growth.
welcome to the ‘new viticulture’. There has been a change in the
way that many of the more enlightened growers are seeing their
vineyards. They are now rightly viewed as agroecosystems, with many
organisms working together of which the vine is but one. In
particular, the rich microbial life of the soil is now appreciated
as being of great importance.
is not just the organic and biodynamic growers who realize that
these agroecosystems matter in their entirety, but also conventional
growers who are choosing to work more sustainably. The science of
integrated pest management/integrated farm management is now pretty
mainstream, and is informing the decisions of growers worldwide.
Vineyards are becoming much healthier places, with the life of the
soil respected, and elegant biological solutions to pest and disease
pressures preferred to ‘magic bullet’ chemical approaches.
really encouraging to see certified sustainable viticultural
programs roll out around the world. In New Zealand, the Sustainable
Viticulture program has a huge take up, and has resulted in massive
reductions in agrochemical use across the industry. In South Africa,
the Integrated Production of Wine program is beginning to take off.
has a sustainable wine certification program that brings together a
number of differing certifying bodies to make a message that is more
easily communicated to consumers. And Chile is currently working
towards developing an independently audited sustainability program.
‘Sustainable wine’ might not be as sexy as biodynamics, but it
has the potential to help the environment – and improve wine
quality as the result of better viticulture – on a much larger
Wine flavour chemistry and the perception of wine
understanding of wine flavour – in terms of both its perception by
humans, and also its basis in wine chemistry – has changed a great
deal in recent years. This is a hugely interesting area of study
that crosses disciplinary boundaries, and even takes in philosophy
is a complex chemical soup. Many of the chemicals in wine have
smells and tastes. But to unentangle which of these chemicals is
most significant is a complicated process, because they interact in
additive ways, there are masking effects, and subthreshold levels of
some chemicals affect the perception of others. The old fashioned
idea is that we can understand the flavour of wine by simply working
out which odour- or taste-active chemicals are present above their
threshold levels in a sort of additive fashion, but this isn’t the
very interesting recent set of studies involved taking the volatile
compounds out of a wine, leaving just the volatile matrix. Then the
volatile compounds can be added back leaving some out, to see what
impact these missing compounds have. This sort of approach is
throwing up some surprising results. In a twist on this theme,
researchers have shown that a wine made up of a red wine
non-volatile matrix and white wine volatiles smells like a red wine,
and vice versa. It’s fascinating stuff.
human perception of wine is really interesting, too. We now realize
that tasting wine involves multisensory perception, with
contributions from the tongue, nose, eyes and even ears. Touch is
another sense that plays a part. All this information is recombined
in the brain and by the time we are aware of it, a lot of processing
has already taken place. Our knowledge or previous experience also
shapes the actual perception of the wine that we have.
addition, individuals differ in their sensitivity to various wine
flavour compounds. A good example is rotundone, a sesquiterpene that
has recently been identified as contributing the peppery flavour
found in red wines such as cool-climate Syrah. One fifth of people
simply can’t detect this at all. There is also work on taste,
showing that around a quarter of people are ‘hypertasters’,
exquisitely sensitive to bitter compounds in particular. Likewise, a
quarter of the population aren’t very sensitive at all to
of work has taken place on Sauvignon Blanc, which is in effect a
‘model system’ for wine. Researchers have shown that the
distinctive aroma of wines made from this variety is largely down to
the presence of two classes of ‘impact’ compound. First, there
are methoxypyrazines, which have green pepper/grassy flavours and
are present in the grapes at harvest, surviving fermentation intact.
there are three polyfunctional thiols, sulfur-containing compounds
formed during fermentation by precursors present in the must: 3MH,
3MHA and 4MMP. These contribute attractive passionfruit, grapefruit
and boxwood aromas. Other compounds involved in Sauvignon aroma
include the various fruity smelling esters, leafy smelling C6
aldehydes and alcohols, and terpenes. Work is underway to connect up
wine chemistry with viticultural and winemaking interventions.
It’s exciting to see this level of understanding emerge, with
contributions from sensory scientists, analytic chemists, molecular
biologists, microbiologists and plant physiologists, as well as the
wine industry itself.
Understanding the role of oxygen in wine
with a view to the future, I’m going to pick two fields that I
think will be particularly influential. The first is that of
understanding the role of oxygen in winemaking and beyond. This is
an area of intense current research, but lots remains to be
discovered. Advances in protecting wine from oxygen – reductive
winemaking – have already permitted winemakers to make wines that
a generation ago simply weren’t possible.
climate wine regions can now make whites and unoaked reds with
incredible freshness of purity of fruit, largely because of the
availability of refrigerated stainless steel tanks and inert gases.
But while protecting wines from oxygen has been a powerful tool for
shaping wine style, the appropriate exposure to oxygen is also
important for making some wines.
this has been achieved through the use of barrels. More recently,
microoxygenation coupled with the use of barrel alternatives has
attempted to replicate this. But microoxygenation is a bit of a dark
art, and the doses delivered are likely much higher than those
delivered by oak barrels, although they are delivered over a shorter
period. Could it be that it is not just the dose of oxygen
delivered, but also the rate, that is critical in terms of the
luminescence-based tools are now available for monitoring oxygen,
and the hope is that studies looking at the effects of different
oxygen regimes—both during winemaking and post-bottling—on a
range of wines, tracking both chemical and sensory targets, could
help reveal the optimal oxygen management techniques for different
styles of wines.
Genetic modification of yeasts and vines
second field for the future is the genetic modification of yeasts
and grapevines. This is highly controversial, of course: many
consumers simply won’t accept wines made from GM vines or yeasts.
As a scientist, I see GM as a very powerful tool, which can be used
for good or evil.
evil use is to produce pesticide and herbicide resistant vines, and
then nuke the vineyard with these chemicals to eradicate all other
life. The good use? Well, GM is the only way you can make existing
varieties (which we very much like) resistant to the ravages of
oidium and downy mildew, which make spraying necessary if a crop is
to be achieved.
vines could be much more environmentally friendly – there
certainly seem to be no safety issues. The problem with GM vines is
that they’d be expensive to produce, and therefore we could end up
with increasing focus on just a few varieties worldwide, which would
be bad news indeed. GM yeasts are already with us. There are
currently two of them being used in the USA. Most other countries
won’t allow them. One is a very low sulfide-producing strain that
also produces reduced levels of ethyl carbamate (although the
manufacturers claim that this is not technically a GM yeast); the
other does malolactic fermentation at the same time as alcoholic
of work is currently going on to produce a yeast that makes less
alcohol from the same amount of sugar in the must: now this would be
really useful. Whether we like it or not, the issue of GM organisms
in wine is not going to go away.
this is just a quick overview of some of the more important
contributions of science to wine. If I can be permitted to dream a
little, if I had a gazillion dollar research budget, I’d use it
for a number of related projects. I’d love to understand what
exactly it is about terroir and viticulture that makes great
vineyards capable of producing great wines. I’d like to know why
biodynamic winegrowers are having such effect. I’d love to know
why so many natural wine show brilliant elegance and complexity. And
I’d like to use this knowledge to help more growers do the same,
making thrilling wines at prices that even the modestly well off can
afford. A truly egalitarian vision of the wine world’s future!
the Australian Wine Research Institute
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