On 21 June, the longest day of the year, Plumpton College, organisers of the Champagne and Sparkling Wine World Championship (CSWWC) and Nyetimber launched the first light strike awareness day to bring the issue to everyone’s attention and to outline the simple steps that can be taken to prevent wine from being irreversibly damaged.

The famous Italian scientist Galileo Galilei is famously quoted as saying ‘wine is sunlight, held together by water’, but once grapes are picked, light becomes the enemy of wine. In the winery, wine is kept in the dark inside tanks, barrels and underground cellars, however, as soon as it is bottled light comes back into the equation.

Light strike taint can develop in less than an hour. It occurs when ultraviolet and visible light react with riboflavin (vitamin B2), naturally present in wine, which oxidises methionine, a sulphur-containing amino acid also present in wine, to form undesirable sulphur compounds such as dimethyl disulphide (aroma of rotting food, sewage) and methanethiol (smell of drains). Light may also react to form aldehydes (cooked vegetable odour) and degrade esters (fruit aromas).

“After seeing so many pictures on Instagram of wines in the sun I thought we needed to make people more aware of the issues,” said Tony Milonowski, lecturer in oenology at Plumpton College. “It isn’t always a fault people think about and I think producers would be shocked by the number of customers who wouldn’t drink their wine again because it has been damaged by light.”

To reduce the risk of damage, winemakers should install lighting that minimises damage in the winery, bottling and storage areas. Winemakers who move wine out of storage for even just half an hour are at risk and should ensure that bottles are kept covered at all times by using black shrink wrap on bins and stillages, or by placing bottled wine immediately into cardboard boxes.

Producers also need to move away from colourless and light coloured glass. Still and sparkling rosé wines are the most commonly affected as many winemakers want to showcase the pink colour of their wines. In the June edition of Vineyard, Matthew Jukes urged producers to move over to dark bottles as soon as possible.

At Nyetimber, winemaker Brad Greatrix is keen to raise awareness of light strike and all Nyetimber’s wines have been filled into dark amber bottles since the 2009 vintage to ensure they are protected.

“Every year a lot of perfectly good wine is spoiled because it is stored in clear bottles and exposed to sunlight or the wrong type of indoor lighting,” said Brad Greatrix. “Once one learns to recognise the sulphury smell of a light affected bottle, you’ll be amazed at how prevalent it is in wines filled into transparent packaging.”

At packaging company Bruni Erben, Mark Crumpton has noticed a positive trend among UK producers to get ahead of the curve and move away from clear bottles. One of Bruni Erben’s standard traditional method sparkling wine bottles is now produced with UVAG, a darker green glass, which refracts about 87% of damaging light.

“There is a slow awakening with winemakers and hopefully this is trickling down to retailers and customers,” said Mark Crumpton. “As the industry grows winemakers are becoming more professional and striving to make improvements, such as moving to darker bottles. Packaging is the last part of the race and you don’t want to be giving up at that point. In October, we are releasing a pure black glass bottle, which might be difficult for winemakers doing secondary fermentations, but we have quoted several customers for this already.”

While producers often blame the trade and the marketing people for demanding clear glass bottles, Tom Stevenson, founder of the CSWWC believes that for the sake of long-term reputation “no self-respecting producer should allow marketing to overrule quality control” and that they “should switch to dark glass bottles, tick the box and move on”.

For those who are determined to have their rosé wine in clear glass, Bruni Erben has developed a coating to satisfy both winemakers, with its technical performance, and marketers, with its ability to showcase pink wine.

“Flint bottles can be sprayed with a UV filter during manufacturing,” said Mark. “That coating acts as a barrier and helps to dissipate the damaging light rays. It is proving to be popular with spirit producers who are creating pink gins.”