Posted On 26 March 2020
The first-time wine was stored in glass bottles for aging was around 1635-1640. That was the time when more and more glassmakers started to use coal furnaces instead of wood furnaces. Glass produced in wood furnaces was very weak and was usually light green or pale blue in colour. The colour came from using a lot of potash or soda (flux) during the making process. This was needed in order to lower the melting temperature of glass. On the other hand, coal furnaces did not need a lot of flux because they could reach higher temperatures thus allowing sand to melt faster. The end product was always coarser, darker, stronger and had a dark green colour.
This was realised by consumers, wine merchants and restaurant owners. Dark green colour soon became a symbol for high quality products. All wineries in France were using them and consequently it soon became part of the tradition. As you can see, the colour of the wine bottle wasn’t really a choice but simply a side-effect of the production method. Later, during the 19th century as technology improved the colour of a bottle didn’t really justify if it was stronger or not.
Green bottles in some areas are used for traditional reasons, but also in the case of red wine to hide any sediments produced during the aging process. The most important reason we use green bottles today is their ability to protect our wine from light. Not only the visible light but mostly the ultraviolet light. Wines exposed to a lot of natural or artificial light (mostly fluorescent light) develop aromas and flavours like cooked cabbage, wet dog and onion.
These wines have “light-struck” flavours. The flavours produced can’t be noticed by humans at very low concentrations, as low as TCA (cork taint), that’s 4ng/l (thousand-millionth of a gram)! The problem is bigger in wines that are lighter and sensitive such as Champagne, white and rose wines. Red wines are less affected because of their darker colour and high phenolic content. If you want to offer the highest protection to your wine you will use an amber bottle. They can block around 97% of the harmful ultraviolent light. On the other hand, green bottles can offer a 63% protection and the clear bottles just a 10% protection.
The reason is purely for marketing purposes. Consumers want to see the yellow-green colour of a Xinisteri and the salmon like colour of a Cypriot rose. These wines are at more risk but they are also consumed within a few months from bottling. The wines are also stored in carton boxes and are only exposed to light when they hit the shelf. For whites that can age for a few years we always use green bottles (usually chardonnay, oak aged sauvignon blanc…) while in whites which can age for 10+ years we use amber bottles (e.g high quality Rieslings). Red wines as mentioned above are somehow protected from light but they are the ones that will be exposed to light for many years. Thus, most red wines are stored in the nicer looking green bottle (intermediate protection) instead of the not so nice amber bottle.
We mentioned above that our wines when exposed to light release sulphurous compounds which have a very bad smell. At the start of this chemical reaction we find a trigger called riboflavin (B2) which reacts with the sulphur amino acids methionine and cysteine which then produce volatile compounds such as dimethylsulphide (cooked cabbage or asparagus aroma), dimethyldisulphide (onion aroma), and hydrogen sulphide(rotten eggs aroma)(Maujean A.1983).
According to Hartley (2008) “The riboflavin molecule was found to be temporarily placed in a more energetic (excited) state by UV and visible light at a wavelength of 375nm and 440nm respectively. Normal sunlight contains both these wavelengths and is therefore capable of exciting the riboflavin. When the excited riboflavin reverted back to its normal(unexcited) state it transferred its excess energy to other constituents of the wine, causing the amino acids to oxidise, degrade and produce the volatile sulphide compounds”.
Riboflavin is found in bigger concentrations in red wine because of the longer maceration process during its making. Besides that, red wines are affected less from light exposure. The main reason for this is the high concentration of phenolic compounds found in red wine which offer protection.
Emond (2001) in her research found that when the excited riboflavin reverts back to its normal state that excess energy absorbed easier by tannins and there is less production of damaging compounds.
Ronald, S, J. (2008). Wine science. Principles and applications, third edition. England. Elsevier.
Maujean, A. and Seguin. (1983). Sunlight flavours in Champagne wines. 3- Photochemical reactions responsible for sunlight flavours in Champagne wine.
Hartley, A. (2008). The Effect of Ultraviolet Light on Wine Quality.
Emond, S. (2001). Literature search on the effect of light on the quality of wine, Report No: PPD/REP/60772, CCFRA Technology LTD, Chipping Camping, UK.
Sally,E. (2009). Light-struck wines? Available from: http://www.winewisdom.com/articles/techie/light-struck-wines/.
by Fikardos Fikardos, assistant winemaker.
