The new wine game:  animal, vegetable, mineral.

The term minerality is bandied around with gay abandon by winemakers and industry alike, who regularly struggle to define it precisely when probed. But “minerality in wine is difficult to define” said Kees van Leeuwen, Professor of Viticulture at ENITA – Bordeaux University, precisely “because it does not refer to a specific substance present in wine.”

This leaves us floundering with an imprecise language to describe the term. Among many, Andrew Jefford has described it as an “absence of fruit, animal, wood.” Others intone the chalky, flinty paradigm. So if it’s not animal, nor fruit nor vegetable, must it be mineral?

Minerality implies a quality innuendo

In trying to unravel minerality, we have to overcome ‘tasting by association’ which is trained into our understandings.  Professor Ulrich Fischer, at the department of viticulture and oenology at Neustadt in Germany said minerality is a “self fulfilling prophecy – you learn Chablis is flinty; Mosel is wet slate. You know you have heritage and you pick it up.”  But if you lick that flint or that piece of Mosel slate, there’s not a lot of direct flavour.

One thing’s for sure. It’s trendy. And there’s an implied quality innuendo when minerality is mentioned. So there is a responsibility not to abuse the term.

For analytical study, certain chemical compounds are attributed to certain aromas, for example the floral character of monoterpenes or the green pepper of methoxypyrazines. The chemical compound can be analysed to study how the character is formed. Yet no one compound has yet been attributed to mineral character, which explains why there is no consensus on its use.  

Sensory analysis

We move from analytical study to sensory study, where studies of sauvignon blanc by Dr. Wendy Parr, sensory scientist at Lincoln University in New Zealand, using experienced wine tasters and winemakers from both NZ and France identified “an aroma and flavour characteristic that they term ‘flinty’, ‘smoky’ (but not smoke ’smoky’), or ‘minerality’.” She added “French people also use the word ‘silex’ to describe this note.”

In an ongoing study of the terroir of riesling in the Mosel, Nahe, Rheinhessen and Pfalz, Fischer and his team “do descriptive analysis, evaluating wines on the intensity of ten aromas, such as citrus, pineapple and floral, and taste. People can perceive smell of mineral wine.  In order to be scientific we have to produce a standard, which is reproducible, so we took small stones, wet them, and we look for a smell which is reminiscent of wet slate, wet pebbles. For the taste we couldn’t yet find a standard, however.”

“The standard for minerality is wet pebbles, wet quartzite” Fischer added, “above all it is a smell. Also think about iodine smell at sea and maybe think about fresh oysters. Ozone is maybe coming close, it fits into the concept. “

The terroir connection

You can have terroir without minerality, but can you have minerality without terroir-expression?  Fischer thinks not, saying “minerality is appreciated by people because it relates to the character of the soil. Since the turn of the century, we’re wanting wines with more individuality . One way is to look for more specific terroir wines; another is to use more spontaneous fermentation. This is why wines are getting more mineral. Many wines are fermented warmer [above 18°C]. The fermentation esters are reduced, and other properties of wine are getting stronger, and one of these seems to be the mineral character.”

Parr concurs. “From our data, it is related to the wines from specific areas. All the wines in our studies are tasted blind in opaque glasses and yet the wines from Loire and Saint Bris, near Chablis, always show up with higher intensity ratings to the flinty notes.“

Another area that scientists so far agree that the root route does not exist, in that minerals taken into the plant are not replicated in the form or proportions they’re represented in the soil and bedrock.

And vines have pretty much the same requirements to photosynthesise wherever they are, and soil can be managed to provide these: liming an acid soil, adding drainage to soil in a region of high rainfall. Van Leewen said: “If wine quality was related to specific minerals such as potassium, phosphorus, iron, trace elements, then quality could be improved by addition of these elements. But viticultural practice shows that, except for the correction of severe deficiencies or the application of excessive fertilisation, wine quality is not easily manipulated in either way by these practices.”

The sulphide connection

Nonetheless, many nutrient-poor soils exist. Indeed the heritage of viticulture is on soils that were too poor or mountainous to grow other crops. An indirect relationship between poor soils, stressed vine growth, and winemaking may come into play, with winemaking accentuating or accessing a terroir effect.

Winemaking consultant Sam Harrop MW said “In Pouilly-Fumé, if you bang two bits of silex together, you get an aroma reminiscent of gunflint. Locals believe these flavours come through in the wine and I’ve tasted plenty of wines from this region with such aromas.  But a sulphide is responsible for this aroma, which occurs during fermentation, so the relationship of terroir and minerality is an indirect one. You can’t get the smell of silex banging together directly into the final wine.”

In addition, he said, winemakers in the classic Loire sauvignon blanc regions “have a less interventionist approach – for example, spontaneous fermentation, extended lees contact, not using nutrient supplement – and working with more turbid juices, which offer a greater concentration of precursors for thiol production. All of these work towards greater sulphides some of which can be really positive, and others not quite so tasty. For example I see guava-like thiol expression from ferments of well-managed turbid musts.”  So thiols are terroir-originated, and expressed by a well-managed fermentation process.

Fischer agreed, adding minerality is “more related to terroir than winemaking, though winemaking has an impact.  It seems to be a reductive character, so keeping wine longer on lees enhances the mineral character.”

A thiol called benzenemethanethiol has been reported by Denis Dubourdieu and colleagues at the University of Bordeaux as one source of a mineral/flinty note in sauvignon blanc. Parr said: “It is assumed that these thiols develop their flavour characteristics during fermentation as the precursor compounds in the grape itself need yeast to produce the thiol and the volatile aspects.”   

While there’s a long way to go, minerality clearly does exist sensorially, though current industry usage of the term is highly individual, and without shared meaning. Until more is known, its use as a means of communication may advisedly be used only under caution.

The issue of ‘reduction under screwcap’ is taken out of the clutches of the closure camps, and the science laid bare.

Stink bombs and the grail of thiol

Oxidation is one thing.  But at the opposite end of the spectrum is ‘reduction’ and wine faults at this end of the continuum have just got trickier.

We’re all familiar with the reductive-state stink-bomb, rotten egg odour of hydrogen sulphide (H2S) and the garlicky, onion and rotten cabbage odours of mercaptans, These are expressions of faulty wines.   

Both of these groups of compounds are sulphur-containing off-odours. As we’ve started to understand more of the chemistry about these and other volatile sulphur compounds (VSCs), some are being implicated as positive flavour attributes in some wines.

Sulphur terminology:

• Sulphides: the sulphides and disulphides. (Though the term is loosely used to mean the off-odour VSCs)  
• Thiols:  A group of compounds previously known as mercaptans. These are susceptible to oxidation.
• H2S: hydrogen sulphide
• VSC or sulphur-like odours (SLOs): Any of the sulphur compounds which can contribute positively or cause reductive off-flavour in wine.

VSCs, and their management, are trendy, because they’re not all bad. Something like a bit of the devil you know does you good. There are some important issues for wine flavour and correctness to be understood:

1. VSCs are related to yeast fermentation, with aroma precursors in grapes
2. Winemaking can clear up some VSCs, but not all
3. There not all bad.  Some VSCs can be good, actively sought-after, complexing components in a wine
4. VSCs are thought to be more frequently seen under closures which have a negligible air ingress  

The Redox Potential

Wine contains sulphides.  The form that these take changes.  And that form is dependent on how much or how little oxygen is around. 

Think of the tightrope walker’s balancing pole.  At one end is ‘reduction’ and at the other is oxidation.

Balance is achievable somewhere along the middle section of the pole. With a bit of oxygen a wine may move a bit towards the oxidation end (high redox potential).  With less and less oxygen, a wines moves towards the reduction end (low redox potential).

Depending on various vineyard and winemaking circumstances, the balance may be tipped a little too much one way or the other, i.e. towards oxidation or reduction.

The lower the redox potential the greater the risk of reduction. The greater the opportunity to form VSCs – good ones and bad ones.

Adrian Coulter, senior oenologist at the AWRI, specialises in off-odour VSCs. He explains the basics part one – chemistry: “One of the ways mercaptans are thought to be formed is by reaction of H2S with wine components. Mercaptans can oxidise to disulphides. Disulphides can be reduced back to mercaptans”.

Dr Alan Limmer, owner of a PhD in chemistry and Stonecroft winery in New Zealand, explains the basics, part two – smell: “Mercaptans oxidise to disulphides. The sensory impact is very different. Disulphides are 20 to 40 times less smelly than mercaptans. So the sulphides have not gone away, with racking for example, just changed to disulphides which smell less. Disulphides can revert back to mercaptans (under reducing conditions). The smell profile changes as soon as you do this. Mercaptans and H2S stink.”

The reversibility of most redox reactions is where some of the problems arise. Non-smelly disulphides can be ‘reduced’ back to very smelly thiols.

Some of the more common VSCs

The good, the bad and the ugly

Generally thiols are both bad and ugly.  H2S and mercaptans definitely stink and cause problems in wine.  But, Limmer says: “The sensory effect of them changes markedly as we add on atoms. For example, figuratively speaking from sewer to lavender with a one-atom change. We get complex flavour compounds which have characters that we associate with being positive. Fresh cut hay for example.”

But there’s no way (yet) to keep the good ones and remove the bad ones.

So much for the bad and the ugly. Some thiols confer attributes we consider positive flavour aromas. Dimethyl sulphide  (DMS) is a case in point.  Coulter said: “At low concentrations, DMS has a blackcurrant aroma and might contribute toward the body of aged white wines. At higher concentrations it is generally regarded as a fault, with cooked corn, cooked tomato and molasses notes.”

A Rhône study into DMS in syrah and grenache showed DMS was released during bottle ageing, giving flavours of ‘truffle, undergrowth, black olive’ usually associated with maturing wines.

But it’s from sauvignon blanc, notably work done by Professor Denis Dubourdieu in Bordeaux, that much new understanding has arisen.  Sauvignon blanc would be nothing without VSCs, plus, of course, a healthy dollop of that defining green pepper note, methoxypyrazine.

VSCs and sauvignon blanc

Some of these VSCs, for example, 4MMP, 3MH and 3MHA, also play a role in the flavour of other grape varieties such as chenin blanc,  gewürztraminer, manseng, muscat and riesling. 

The grail of thiol – control and management

VSCs are in wine. Full stop. Yeast make H2S and other reductive odours. The amount of nitrogen during fermentation is a fundamental driver of VSC development.  Limmer said: “Throughout fermentation wines accumulate a range of sulphide compounds. What varies is the amounts of these compounds. And the pattern varies from wine to wine. If there is insufficient nitrogen, yeast use sulphur-containing amino acids as a nitrogen source. There also appears to be an underlying yeast genetic link to the sulphide profile.”  So nitrogen is just one of the determining components.   

Keeping yeast happily fed with nitrogen keeps down the volume of VSCs.  Aerating wine oxidises mercaptans to disulphides, and ‘blows off’ H2S, which is oxidised to elemental sulphur.  Regularly stirring lees avoids reducing conditions building up.  Leaving lees without stirring builds up reducing conditions.

Copper sulphate fining can remove H2S and, to a certain extent, mercaptans, but will not touch the disulphides. Coulter said: “You have to create reducing conditions to get disulphides back to mercaptans.  Then you can copper fine. If a wine is in barrel, put it in tank, add SO2, wait a week and do a copper trial.”

Additionally, copper sulphate fining doesn’t distinguish between the desirable thiols and the undesirable ones.  It takes them all.

Prevention is always better than cure.  Professor Dr Doris Rauhut, specialist in off flavours in wine at Geisenheim Research Centre said: “Bad thiols mask the good ones. If you can minimise the bad ones, the good ones are more noticeable. Positive thiols occur in precursors (in the grape) which are not volatile. They are released during yeast activity.  

“It’s often better to avoid the development of bad thiols early enough, then you don’t need further treatment in the wine” such as copper fining. This way the overall flavour of some varieties can be optimised. 

Rauhut is working on early detection systems so that with the right yeast strain and optimal initial nutrient composition the fermentation can be controlled early to prevent off flavour VSCs from forming. Leaving the good ones on centre stage.

Genie in the bottle

While aeration and copper sulphate fining are useful tools for bulk wine, once the wine is bottled chemical reactions don’t stop.  They are dependent on the redox potential – how much oxygen is available post bottling, or can ingress post bottling, for the oxidation of smelly thiol back to non-smelly disulphide.  They’re also dependent on the amount of reducing agent – free SO2.

In the opposite vein, if non-smelly disulphides are bottled these are then free to reduce back to smelly mercaptans. (under reducing conditions).  Changes keep going over time, which explains why some wines are clean and fresh, fine and dandy one moment, but 12 to 24 months later, under reducing conditions, smelly thiols have taken over the front seat.

It’s not just the aroma that’s affected. Limmer said: “The biggest effect of VSCs is on the palate. Sulphide components affect the palate more than the aroma. In whites, the palate is shortened, with a clunky, hard, bitter, finish. The wine doesn’t finish in accordance to expectation.

“In good reds there is a silky integration of structural tannin. When sulphides are on top of this, the tannins get hard, sometimes with a green tannin edge. When you take out the sulphur, the velvety texture of tannin comes through again, which is how the winemaker intended.”

Desperately seeking VSCs

A number of Australian producers are looking to gain complexity in their wines by retaining some of these VSCs.  Steve Webber, manager and winemaker at De Bortoli said he’s looking for “minerality, texture and the right kind of mercaptans”.  He said it’s about “extracting the right phenolics from the stems and the skins – sulphur-containing amino acids.”

But get this wrong you lose mineral definition on the palate and you get bad mercaptans. “Good mercaptans” he said “highlight mineral, flinty, gunsmoke characters” in sauvignon blanc.  He also talked of the mealy, mineral characters he’s looking for in chardonnay. 

The six million dollar question – are screwcaps implicated? 

This is emotive and politically charged territory. The arguments currently revolve around air ingress, which is not necessarily a closure-specific aspect, and there is not yet a definitive answer.

Limmer said: “When the wine is bottled the compounds (disulphides) are still in there, you just can’t see them. Over time they break down and revert (reduce) to thiols.  There is an accumulation of smelly thiols in bottle.  And we’re seeing a difference under screwcap and cork. The same problem has been created under cork by sealing the top of the cork. Trials show the biggest problem is in wine sealed under ampoule.  It is suggested to be an oxygen ingress issue, but we don’t know this for certain.”

At the Geisenheim Research Centre in Germany, closure specialist Dr Rainer Jung said: “Our experience is that it hasn’t happened here.  We have used screwcaps since the 1970s for experimental wines and I never had the problem that wine with screwcap has a reductive character.”

Jung speculated why, saying: “In Germany few people put inert gas in the headspace so there is more oxygen in the headspace. In the first year of storage the loss of SO2 is little bit higher for screwcap-bottled wine because of the bigger headspace (in comparison to cork). Except if you add CO2 or nitrogen in the headspace. And it equalises after a time because screwcap is more dense.”

Coulter said: “Winemakers work hard to avoid sulphur off-odours, however, given that we don’t yet understand all the reactions that occur and the factors that influence them, the formation of these compounds is sometimes beyond winemakers’ control.”

In the end

VSCs are the new frontier of winemaking.  We don’t yet know how to keep the good ones and remove the bad ones. We don’t know how much oxygen is just the right amount, but it varies with grape variety, viticulture and winemaking. We don’t know what is a good closure.  And we don’t know how much VSC is a good thing or how to keep it at an optimum level in bottle.  It’s a little akin to the volatile acidity issue or the brett issue, where a little bit can add complexity and too much is a fault. And views on when one moves from good to bad vary with the individual.

Excess sulphur dioxide is not considered to be an off-odour VSC

• SO2 is an antimicrobial and antioxidant.
• SO2 is not a sulphide.
• Enough needs to be added to prevent the wine from oxidising, but not so much as to destroy flavour.
• Too much free SO2 smells sulphury, like burnt match, a sharp, acrid smell.
• However, being a reducing agent SO2 can help break down non-smelly disulphides to smelly thiols.

Light is well known to promote chemical changes in foodstuffs.

Brewers have know about the flavour impact of light on beer for many years.  It’s widely reported in the beer industry that beer goes ’skunky’ when it’s exposed to light, even just in the time it takes you to nurse your beer on a lazy summer’s afternoon. 

Beer off flavour in the presence of light was noted as long ago as 1875, which is why, until the marketeers got involved, pretty much all beer was bottled in dark glass, amber having been found to be the best at filtering out most of the harming wavelengths.  

For wines, it is much more of an issue for whites and rosés. In reds the high tannin content offers a protective veil, binding riboflavin (more below).  And the issue can pretty much be avoided by using amber bottles, but with the marketing of any product, many considerations are important, not least the packaging, and we are seeing an increasing number of packaging options including clear glass, in both the beer and wine aisles.

A photochemical reaction occurs in both beer and wine. The responsible light wavelengths are between 350-500 nm, but activity is noted to peak at 370 and 440 nm, so in the near-ultraviolet and part of the visible wavelengths. Amber bottles filter out 97-98% of these wavelengths, which is why they’re the best. Dark green glass filters out just 63% of these critical wavelengths, while white flint (clear) glass filters a meagre 10%, so it’s only when we put beer and wine into clear glass (either bottles for the shop or pints/wine glasses for the garden) that the light degradation issue arises.

Light penetrating the glass excites riboflavin (vitamin B2, present in beer in concentrations around 1mg/litre, and in wine at concentrations at 0.4mg/litre), which acts as a catalyst, cleaving the compounds responsible for the classic bitter flavours in beer.

In wine, riboflavin, found naturally in must, reacts with cysteine and methionine (amino acids). Wine naturally contains 1-4g/l of amino acids. This reaction forms hydrogen sulphide and mercaptans, notably 3-methyl-2-butene-1-thiol (MBT).  MBT is the skunky thiol (mercaptan), smelling pungently of leek, onion, cooked cabbage, wet wool, soy etc. It is highly flavour and aroma active, and humans can smell it at concentrations similar to TCA, namely about 4 ng/l. In pale beer concentrations as low as 1ng/l can make the beer unpalatable. 

Paul Hegarty, head of communications for Coors brewers, has 15 years technical experience for brewers where ’sunstruck’ was high on the agenda. He was prosaic about the issue for beer, saying ”light struck has a skunky character, and rubbery – the flavour of beer when you’re sitting in the garden on a sunny afternoon.  Experts might define it as a fault, but consumers might quite like it.  It reminds them of sunny holidays.”  

Dr Ellen Norman, head of  analytical development and Brewing Research International said: “Research has suggested that consumers do not agree on whether they view lightstruck as a negative flavour in beer – some actually prefer it. We have also seen studies where consumers are unable to pick up differences between a beer before and after the beer has sat in the light.”

However, hop cones can be extracted using supercritical CO2 (of late renowned in the wine industry for reducing TCA levels in cork granules). The MBT-forming compounds undergo another process to make them light-stable, enabling the resulting beer to be stored safely in clear glass.  It is thought the number of brands produced using these processed hop products is relatively low.

Wine’s propensity to reductive flavours

But wine never got that ’skunky’ aroma. Peter Godden, group manager of industry development and support, at AWRI, said: “the formation of lightstruck flavour is exacerbated by low oxygen in both beer and wine, where the wine already has a propensity to develop reductive characters, but the reasons for this are different for beer and wine, because the compounds thought to be responsible in beer do not exist in wine.  However, lees-aged sparkling wine may be an exception, containing more methionine, and other compounds, than other wines, and so may therefore be susceptible to formation of lightstruck flavour through a mechanism that is similar to that in beer.”

We know some grape varieties and wine styles are more susceptible to reductive characters than others. Not every wine reacts the same way.  It also depends on how the wine is made, and how many amino acids it contains. Given the right (or wrong) light conditions, mercaptans develop. Gerd Stepp, who was winemaker for Marks and Spencer at the time (now consulting to them), explained: “mercapans are relevant in winemaking.  A lot of the precursor in wine is hydrogen disulphide (H2S). H2S has a high threshold, but it can continue to mercaptans, and these have a low threshold [4 ng/l].  So tiny amounts of H2S, almost undetectable, [can go into the bottle] but once the bottle is closed, the wine can develop hints of mercaptan.”

In the case of lightstruck cysteine and methionine amino acids come from yeast autolysis, the time spent on lees. Thus it is not so common to find champagne in clear glass. For wine with low amino acid content, so without lees contact, the chance for wine  to get lightstruck is much smaller. But, Stepp added: “You taste it much more easily in aromatic or neutral white wine, onion flavours come through.  With red wines there is more air, oak, open rackings, so H2S is lower.”

Paolo Bisol of Ruggeri said: “Our rosé has been in clear glass since 1950, but pinot bianco and pinot nero are less sensitive.  It might be better in dark glass, but you can see the colour. However, it is important for prosecco to be in dark glass because prosecco is sensitive to light.  It is light, fresh, young and fruity.” 

Sparklers

Wines such as traditional method sparklers, with their long lees ageing and consequently high amino acid content are susceptible to light struck.  Jean-Baptiste Lécaillon, director of vineyards and wines, and chef de caves at Champagne Louis Roederer said: “amino-acids such as cysteine are very important in wine as they are responsible for aromatic structure of the wines. In the case of sparkling, a large part of the aromatic profile is due to autolysis of yeast proteins. During the autolysis, some enzymatic reactions separate the proteins into thousands of amino-acids that are aromatic and responsible for the “yeasty”, “nutty” characters.”

He offered a number of solutions.  “Our only focus is to protect the wine from UV. You can do it by using green bottles that filter 92% of the UV, which is enough to protect the wine during a reasonable sun exposure. A strong sun exposure would be bad for any compounds of the wine…. so it is to be avoided.  For Cristal we protect the clear bottles with coloured cellophane. This cellophane is specially designed to filter 98% of the UV, which means, if the bottles stay wrapped, it is better protected than a green bottle. This is why we add in all our cases of Cristal a leaflet which recommends keeping the cellophane until the last moment.”  Of course this doesn’t mean the retailer or consumer will keep the cellophane on. The bottle looks pretty stylish without the foil, even with a warning note.

Marks & Spencer

Marks & Spencer use no clear glass at all for their wine range.  Five or six years ago all the wines were moved to green or amber glass. Stepp said: “If wine is in a presentation box then it might be in clear glass e.g. champagne, but the box protects the wine.”

But it’s not always  easy to get the most protective colour of glass. Stepp said: “UVAG green [a type of bottle colour] has a higher UV protective quality, they use a different oxide for colouring. But it is limited by availability, so we have to see if we can find it on the local market, and if not we go with the normal green.” He said it costs too much to transport empty UVAG bottles to the country of bottling.

The M&S policy makes it difficult to draw attention to their rosé wines, which many other retailers and brand owners market in clear glass to draw attention to their attractive colour and mood suggestions.  The M&S technical team insist on green glass to protect the wine, and this outweighs any marketing considerations. To signify rosé to consumers, the bottles all have overtly pink labels and distinctive pink capsules of the same hue to illustrate the wine’s tint.

Stepp said: “Commercially and presentationally it is quite a challenge. The rosé wine colour is less visible, and the colour of rosé is one of the key features of selling a rosé. Green glass is less attractive.”

Clear glass coating

There has been some experimentation with coatings over clear glass which filter the UV and allow the presentational benefits of clear glass. Godden said: “In 2001 we conducted a trial using a clear plasticised coating for the outer surface of clear glass bottles. Its purpose was to block UV light from damaging wine. A chardonnay wine was packaged in coated bottles, and also in the same bottle without the coating. The bottles were then exposed to UV light (approximately 50 cm from the light source of approximately 360 nm) for 21 days.

“During sensory evaluation the wine in the coated bottles was rated higher for freshness and for fruit characters, and lower for a whole range of reductive descriptors (reduced sulphur, smoky, burnt rubber, bacon, burnt match, gunsmoke etc.). The results were highly statistically significant – the coating appeared to work extremely well.”

Stepp explained why M&S had not pursued this option.  “A UV protective coating can be applied once the bottle is finished.. The coating has to be completely transparent on clear glass, otherwise it defeats the purpose. But if the coating is 100% clear, its protection only goes to 400nm. So the 440nm peak was not covered.  And to get protection over 400nm, the protective coating becomes coloured.”

Greater UV protective capabilities give a cloudy quality to the film, which may explain a lack of progression with this technology. Stepp suggested this avenue may still be worth exploring if there is some kind of bottle coating that is an improvement on what’s currently avail in the industry. 

The in-store environment

In a store environment under some types of fluorescent lighting wine in clear glass can develop noticeable degradation flavours after just a few hours.  Stepp said: “Green glass protection is not 100%, so store lighting is also important, as is stock rotation.  It doesn’t take long for mercaptans to form.  Generally the degradation of quality on shelf in clear glass would be quite high. Rosé is slightly more unstable because colour can turn. We’ve done a lot of work in store lighting, we’ve done tests with filters on certain light. We are using lights now that are better. And this is also relevant for other products, chocolate sensitive to light. 

Howard Winn, who was quality manager for beers, wines and spirits at Sainsbury’s, said: “We have a few wines in flint glass, mainly the usual suspects, rosé, sweet Bordeaux. It is an ongoing project to move away from fluorescent lighting, reducing the lighting in the BWS [beers, wines and spirits] aisles and moving to lower energy lights positioned away from the fixtures.  Deeper steel shelves have also helped reduce the exposure of bottles to light.  Our lighter sherry styles have recently been moved to different glass which offers higher UV protection.  Similarly our rosé Champagne moved to green glass a couple of years ago.  It’s all about protecting the wine.

Lecaillon was optimistic about the trade’s level of knowledge: “there is the question of bottle shops and fridges, It is obvious that if the wine is under full light for a while, there is an important risk of light struck, but I believe the trade is aware of that problem and take all necessary measures to protect the wine.”

With all the right precautions, light struck need not be a big issue, but the creative tension between brand image and positioning, and technical precision, means the issue is still relevant.  Stepp offers yet another option, saying: “There is quite a bit of work from our side on the wine making.  If we did progress on clear glass with rosé we would want to make the wines in a way that they are less prone to mercaptans, for example, have less of the amino acids cysteine and methionine; have a slightly faster fermentation, focusing on fresh fruit flavours with less lees contact. Our experiments are ongoing.”