Is too much sunshine ruining your picnics and barbeques?

The famous Italian scientist Galileo Galilei is quoted as saying “Wine is sunlight, held together by water”, but, once the grapes are picked, light becomes the enemy. Winemakers keep it in the dark: inside tanks, barrels and underground cellars. Only once the wine is bottled does it come back into the light, and this can ruin wine in less than an hour.

Summer solstice is the longest day of the year, but as we enjoy our socially-distanced picnics, barbeques and other outdoor events, is this sunshine ruining the wines?

Plumpton Wine Division, (UK’s centre of Excellence in wine education, research and training), The Champagne & Sparkling Wine World Championships (CSWWC), and Brad Greatrix, winemaker at Nyetimber, have once again joined forces to raise and drive the awareness of the dangers of Light Strike, particularly for wines bottled in clear glass.

With the support of Wine GB (as part of English Wine Week), Plumpton Wine Division, CSWWC and Brad Greatrix, are urging winemakers, wine merchants and customers to take action.

“At Plumpton College, the UK centre of excellence in wine education, training and research, light strike has been on the syllabus for many years and a number of research projects have been conducted. All wine graduates have a clear understanding of the risks involved”, commented Dr Greg Dunn, Head of Plumpton Wine Division. “However, many in the broader wine trade and general public remain oblivious to this problem. So, we are using the summer solstice as Light Strike Awareness Day, the aim of which is to highlight the problem of light strike to as far and as wide as possible, and to outline the simple steps that can be taken to prevent wine from being irreversibly damaged.”

Plumpton Wine Estate recently took the final steps to move their sparkling Rose into green glass.

Light strike taint or Goût de Lumière occurs when ultraviolet and certain visible light wavelengths react with the wine within in as little as 60 minutes to produce unpleasant sulphur compounds.

“Light strike taints can start to develop as soon as the wine bottle is removed from its cardboard box.” commented Tom Stevenson, the UK sparkling wine expert, founder of the CSWWC, and the first person to demonstrate to a live audience (ISWS 2013) the progressively foul light strike aromas in the same bottled in different coloured glass. He states “Clear glass is most commonly used for Rosé and Blanc de Blancs styles. Producers always blame the marketing people for demanding clear glass bottles and whereas this might be true, it is a fundamentally a quality control issue, and for the sake of longterm reputation, no self-respecting producer should allow marketing to overrule quality control. They should switch to dark glass bottles, tick the box and move on. English sparkling wine is ahead of the game, as is Trentodoc, but Champagne lags behind. All the clear glass bottles in my cellar have always been double-bagged in black plastic and since I introduced this safeguard at the CSWWC in 2015, the instance of faulty bottles has dropped by 94%”

Brad Greatrix, winemaker for Nyetimber is hugely passionate about the topic of light strike.

“I do as much as I can to raise awareness of light strike. 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. At Nyetimber we’ve been filling our wines into dark amber bottles since the 2009 vintage to protect against these exposures. 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!”

Still and sparkling rosé wines are the most commonly affected, as many winemakers still choose to showcase the pink colour of their wines through colourless glass.

The team have put together the following aids to support each group:

Winemakers

  • Should package their wines in dark glass bottles (coloured wrapping and individual cardboard containers are band-aids quickly pulled off by consumers).
  • Until you stop using clear glass bottles, ensure bottles are kept covered at all times in the winery, by using opaque shrink wrap on bins and stillages, or by placing wine immediately into cardboard boxes.
  • Installing lighting that minimises damage to wine in the winery, bottling and storage areas (even green bottles offer only 50% protection).

Wine merchants, bars and restaurants

  • Keep stock at risk of light strike away from direct light, including window displays.
  • Change damaging lighting such as fluorescents tubes to more wine-friendly low energy bulbs.
  • Stock wines from wineries who package their wine in dark glass.

Customers

  • Keep wine at home in cardboard boxes and in cool dark locations.
  • When enjoying wine outside, keep the wine away from direct light, or even better, wrap the bottle in aluminium foil.
  • Choose wines packaged in dark glass.

Light strike: the facts

Most susceptible wine styles:

  • Sparkling white and rosé, due to extended lees ageing
  • Still white and rosé wine

Most damaging light             

  • Wavelengths below 510 nm, particularly between 370nm (UV) and 442nm (blue).
  • Direct sunlight
  • Fluorescent tubes, xenon and metal halide lamps in close proximity to wine

Most susceptible glass bottles:

  • Colourless or flint glass
  • Blue coloured bottles
  • Light green coloured bottle

Glass bottles providing greater protections

  • Bottles with opaque coverings
  • Dark brown bottles
  • Amber bottles
  • Dark green bottles

Key reactions                   

Light reacts with riboflavin (vitamin B2), naturally present in wine, which photo-oxidises methionine (a sulphur-containing amino acid also present in wine) and to form undesirable sulphur compounds such as dimethyldisulphide or DMDS (onions, cooked cabbage), dimethylsulphide or DMS (stale cabbage), hydrogen sulphide or H2S (rotten eggs), methanethiol or MT (halitosis, stagnant water), and ethyl methyl sulphide or EMS (wet wool). Initially the smell can be just off or not clean, but put all these compounds together and they will build into the smell of rotting flesh and sewage. Light may also bleach or yellow the colour of a wine and degrade the fruity aromas of esters.