Dr. Carien Coetzee
29 August 2021
Exposure to light can potentially induce major changes to a wine’s composition. This effect mainly occurs in bottled white and rosé wines exposed to light1 and is commonly referred to as the “light-struck taste”, “taste of light” or, in French, “goût de lumière”.
Light-strike wines typically have unpleasant aromas2–5 with “reductive”-type attributes described as “rotten egg”, “garlic”, “onion” and “boiled cabbage”. In some cases, the wine can also turn brown and develop a metallic taste1.
What causes Light-Strike in wine?
Light-induced changes in wine are mainly due to photochemical oxidation reactions which may affect many wine components resulting in changes in aroma and colour4,6–8. There is one compound that plays an integral role in light-induced reactions in wine. This compound is riboflavin (or vitamin B2).
Riboflavin is a highly photosensitive compound and serves as a photochemical activator when exposed to light. The key reaction causing Light-Strike is between such a photochemical activator and sulphur-containing amino acids, such as methionine and cysteine, all of which naturally occur in wine. Catalysed by ultraviolet radiation, these compounds react to form volatile compounds such as dimethylsulphide (DMS), dimethyldisulphide (DMDS), and hydrogen sulphide (H2S)9. These compounds are typically responsible for the unpleasant “reductive” aroma attributes mentioned earlier.
Other light-induced reactions that can also contribute to Light-Strike in wines include the formation of furfural (which has been positively correlated to the “cooked vegetable” aroma of white wines stored under oxidative conditions10,11) and the oxidation of ethanol producing acetaldehyde (effect reported in model wine)7. The interconversion of diethyl disulfide and ethanethiol in the presence of sulfites has also been reported12.
Riboflavin concentrations in wine
Riboflavin content in the grape berry is typically very low (3-60 μg/L)13,14. However, relatively higher concentrations in the grapes (e.g. 30-50 μg/L) can lead to higher riboflavin concentrations in the resulting wine.
The main source of riboflavin is the metabolic activity of Saccharomyces cerevisiae during alcoholic fermentation. Some yeast strains have the ability to produce high concentrations of riboflavin and the formation of more than 200 μg/L have been reported15 in finished wines. The highest concentration found in literature is 350 μg/L15,16.
Lower riboflavin concentrations (lower than 80-100 μg/L) could limit the risk of the development of the Light-Strike in wines14. When the riboflavin concentration in wine is greater than 100 μg/L, the wine is considered to have a high risk of presenting the taint16.
Yeast, nutrients and riboflavin
Yeast strains differ in their riboflavin forming capabilities. In a study14, 15 commercial yeast strains were used to ferment Chardonnay grape juice containing 5 μg/L riboflavin:
- 9 x Saccharomyces cerevisiae
- 5 x Saccharomyces bayanus
- 1 x Saccharomyces uvarum
Results showed that half of the tested yeasts produced low concentrations of riboflavin (less than 50 μg/L) and the other half produced more than 50 μg/L. Three of the strains produced more than 100 μg/L which could potentially lead to the development of Light-Strike in wines.
The riboflavin producing yeast strains have occasionally been found to be methionine producing as well, which may increase the risk of spoilage even further14. Low riboflavin producing yeast strains can thus be used as a tool to limit riboflavin formation and therefore minimize the risk of Light-Strike in wines.
Complex yeast nutrients (based on yeast extract) commonly used during winemaking usually contains vitamins, including riboflavin14 and can therefore potentially contribute significantly to the final riboflavin concentration in the finished wines. Results from a study performed using different yeast nutrients showed that nutrients based on yeast cell walls resulted in a wine with higher riboflavin content when compared to the use of inorganic nutrients based on diammonium phosphate (DAP)1. Higher riboflavin concentrations were also obtained by ageing wine on the yeast lees15. Care should be taken when choosing oenological products as certain preparations can support the release of riboflavin.
Testing your wine for Light-Strike
Exposure of wine to light at wavelengths between 370 and 450 nm (corresponding to the highest visible light absorption of riboflavin17) can serve as a test to determine if a wine is susceptible to Light-Strike. When performing this test, it is important to include a range of wavelengths as studies have shown that different light sources resulted in different volatile sulphur concentrations in white wine bottled in clear glass1.
EVER Solutions offer testing technology called “Light 7 stress” which is a unique tool equipped with LED technology that recreates the entire light spectrum to assess the effects of light stress on wine. This test will verify a wine’s predisposition to Light-Strike.
Light exposure can result in what is known as light-struck flavours and aromas in wines. These are produced by the initiation of chemical reactions, resulting in the formation of sulphurous compounds with an unpleasant smell and taste.
Part 1 of this blog series briefly discussed the effect of Light-Strike, the mechanism involved, the prevalence and formation of riboflavin in wines and options for testing wines for predisposition to Light-Strike. Part 2 of this series will discuss options for preventing Light-Strike and lowering the risk of Light-Strike from occurring by reducing the riboflavin concentration in wine.
(1) María Mislata, A.; Puxeu, M.; Mestres, M.; Ferrer-Gallego, R. The Light Struck Taste of Wines. In Grapes and Wine; IntechOpen, 2021. https://doi.org/10.5772/intechopen.99279.
(2) Haye, B.; Maujean, A.; Jacquemin, C.; Feuillat, M. Contribution a l’étude Des “Goûts de Lumière” Dans Le Vin de Champagne. I. Aspects Analytiques. Dosage Des Mercaptans et Des Thiols Dans Les Vins. Connaissance de la Vigne et du Vin 1977, 11, 243–254.
(3) Dias, D. A.; Clark, A. C.; Smith, T. A.; Ghiggino, K. P.; Scollary, G. R. Wine Bottle Colour and Oxidative Spoilage: Whole Bottle Light Exposure Experiments under Controlled and Uncontrolled Temperature Conditions. Food Chemistry 2013, 138 (4), 2451–2459. https://doi.org/10.1016/j.foodchem.2012.12.024.
(4) Dias, D. A.; Smith, T. A.; Ghiggino, K. P.; Scollary, G. R. The Role of Light, Temperature and Wine Bottle Colour on Pigment Enhancement in White Wine. Food Chemistry 2012, 135 (4), 2934–2941. https://doi.org/10.1016/j.foodchem.2012.07.068.
(5) Pripi-Nicolau, L.; De Revel, G.; Bertrand, A.; Maujean, A. Formation of Flavor Components by the Reaction of Amino Acid and Carbonyl Compounds in Mild Conditions. Journal of Agricultural and Food Chemistry 2000, 48 (9), 3761–3766. https://doi.org/10.1021/jf991024w.
(6) Andrés-Lacueva, C.; Mattivi, F.; Tonon, D. Determination of Riboflavin, Flavin Mononucleotide and Flavin-Adenine Dinucleotide in Wine and Other Beverages by High-Performance Liquid Chromatography with Fluorescence Detection. Journal of Chromatography A 1998, 823 (1–2), 355–363. https://doi.org/10.1016/S0021-9673(98)00585-8.
(7) CLARK, A.; PRENZLER, P.; SCOLLARY, G. Impact of the Condition of Storage of Tartaric Acid Solutions on the Production and Stability of Glyoxylic Acid. Food Chemistry 2007, 102 (3), 905–916. https://doi.org/10.1016/j.foodchem.2006.06.029.
(8) Clark, A. C.; Dias, D. A.; Smith, T. A.; Ghiggino, K. P.; Scollary, G. R. Iron(III) Tartrate as a Potential Precursor of Light-Induced Oxidative Degradation of White Wine: Studies in a Model Wine System. Journal of Agricultural and Food Chemistry 2011, 59 (8), 3575–3581. https://doi.org/10.1021/jf104897z.
(9) Hartley, A. The Effect of Ultraviolet Light on Wine Quality. WRAP.org.uk 2008.
(10) Escudero, A.; Hernández-Orte, P.; Cacho, J.; Ferreira, V. Clues about the Role of Methional As Character Impact Odorant of Some Oxidized Wines. Journal of Agricultural and Food Chemistry 2000, 48 (9), 4268–4272. https://doi.org/10.1021/jf991177j.
(11) Escudero, A.; Asencio, E.; Cacho, J.; Ferreira, V. Sensory and Chemical Changes of Young White Wines Stored under Oxygen. An Assessment of the Role Played by Aldehydes and Some Other Important Odorants. Food Chemistry 2002, 77 (3), 325–331.
(12) Bobet, R. A.; Noble, A. C.; Boulton, R. B. Kinetics of the Ethanethiol and Diethyl Disulfide Interconversion in Wine-like Solutions. Journal of Agricultural and Food Chemistry 1990, 38 (2), 449–452. https://doi.org/10.1021/jf00092a025.
(13) Ribereau-Gayon, P.; Boidron, J. N.; Terrier, a. Aroma of Muscat Grape Varieties. Journal of Agricultural and Food Chemistry 1975, 23 (6), 1042–1047. https://doi.org/10.1021/jf60202a050.
(14) Fracassetti, D.; Gabrielli, M.; Encinas, J.; Manara, M.; Pellegrino, I.; Tirelli, A.; Sciences, N.; Gildo, D. C. Approaches to Prevent the Light-Struck Taste in White Wine. 2012. https://doi.org/10.1111/ajgw.12295.
(15) Ournac, A. Riboflavine Pendant La Fermentation Du Jus de Raisin et La Conservation Du Vin Sur Lies. Annales de Technologie Agricole 1968, 17.
(16) Pichler, U. Analisi Della Riboflavina Nei Vini Bianchi e Influenza Della Sua Concentrazione. L’Enotecnico 1996, 32, 57–62.
(17) Maujean, A.; Seguin, N. Contribution à l’étude Des Goûts de Lumière Dans Les Vins de Champagne. 3. Les Réactions Photochimiques Responsables Des Goûts de Lumière Dans Le Vin de Champagne. Sciences des Aliments 1983, 3, 589– 601
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