Faults, Flaws & Taints
This page, which regularly changes, provides discussion of various faults, flaws and taints that may affect wine. The current topic is lightstrike.
Lightstrike may affect wines bottled in clear glass (flint) bottles. The fault, which can haveserious organoleptic impacts, is most likely to affect sparkling wines and white and rosé wines - red wines have a higher degree of protection due to their higher levels of phenols.
Lightstrike also affects milk, and beers - thankfully most ales or bottled in brown glass - and brewers have to adjust hopping regimes if the marketing departments insist that they are bottled in clear bottles. Whilst there can be little doubt that white and rosé wines can look tempting when bottled in clear glass, there is no doubt whatsoever that this can be hugely damaging to the product. The photo taken in a supermarket in France, shows two bottles of Sauternes from the same property and same vintage. The bottle on the left has been taken from the shelf and is the victim of lightstrike, the bottle on the right is newly removed from the carton.
Louis Roederer Cristal, regarded by many as a particularly fine 'de-luxe cuvée' Champagne, is bottled in clear glass, but this is wrapped in orange coloured cellophane, which filters up to 98% of UV light. Interestingly, Louis Roederer was the first major Champagne house to switch to brown (amber) bottles (for wines other than Cristal) in 2010; since then, several other houses have followed suit including Piper-Heidsieck and Drapier, so it would seem that at last the Champagne industry is beginning to take the problem seriously.
How to detect affected wines:
How to detect affected wines: On the appearance, there is a deepening of colour, sometimes considerably so. The nose may exude odours of sulfur, skunk, garlic, or cooked cabbage. There can also be aromas of 'marmite', wet wool, or wet cardboard. However, wet cardboard aromas can also result from poor filtration, and wet wool aromas are sometimes associated with the Chenin Blanc grape variety.
Causes of the Fault:
The Transmission of UV Light Through Clear Glass Bottles Lightstrike is found in wines that have been exposed to UV light and visible light at low wavelengths. The severity of the fault may depend upon the following:
- The spectrum of the light source
- The intensity of the light
- The irradiation duration
- The optical properties of the bottle
- The light absorbing species and composition of the wine
With regard to the spectrum of the light source, the most damaging wavelengths to wine are below 520nm, especially in the range of 325-450 nm.
The Role of Riboflavin, Sulfur-Containing Amino Acids, and Iron Tartrate
Certain Volatile Sulfur Compounds are produced from riboflavin and amino acids by a photochemical reaction with light. Riboflavin (vitamin B2) is a very photosensitive compound and has strong absorption of UV light. It occurs naturally in grapes, at a concentration of approximately around 50-70 μg/l, and further amounts are produced during the fermentation by yeast and
released during autolysis. Following fermentation, the level may reach 110-250 μg/l. If the wine is aged on the lees, the level will increase further. An average level in white wines is perhaps 100 μg/l. A level of riboflavin below 80-100 μg/l could limit the development of lightstrike.
Treatment
There is no treatment. The fault is irreversible. More information on this topic is contained in my new book: Wine Faults and Flaws: A Practical Guide | Wiley