| The short answer is that light can definitely affect | | | | reaction. |
| wine, but we need to take a closer look at the | | | | Research has shown that wavelengths in the |
| physics and chemistry of it all to understand why | | | | 375-440 nm range-that is, the high end of the |
| and how in what is called light-strike reactions, | | | | UVA range and the blue (low) end of the visible |
| which can impart off-odors to wine, what the | | | | light range-are most damaging to wine. The |
| French call goût de lumière. | | | | amount of radiation absorbed by wine in this |
| Wine is sensitive to the damaging rays of light, | | | | range is directly proportional to opacity; therefore, |
| particularly ultraviolet (UV) rays from sunlight and | | | | red wine absorbs the most, and is most affected, |
| fluorescent lighting; that's why wine (and beer) is | | | | while white wine absorbs the least-rosé |
| packaged in dark bottles-the best example is Port | | | | wine is in the middle. As such, for marketing |
| in those familiar, dark, opaque bottles. Wines | | | | purpose where displaying color is important, white |
| packaged in clear glass bottles are meant for | | | | wine can be stored in clear glass, although not for |
| quick consumption and should be stored in carton | | | | extended periods of time; that's why premium |
| boxes until such a time. | | | | whites, such as age-worthy Chablis wines come in |
| All forms of radiation, including visible light | | | | dead-leaf-colored glass, a golden-yellow color that |
| ultraviolet (UV) rays and X-rays, have energy | | | | provides better protection than green. |
| that is directly proportional to their frequencies or | | | | Opaque, deeply colored, rich reds absorb almost all |
| inversely proportional to their wavelengths-that is, | | | | radiation; however, these have the highest |
| high-frequency waves have short wavelengths, | | | | concentration of effect-inhibiting tannins, which |
| and vice versa. And the greater the energy, the | | | | provide protection. But if the concentration is low |
| greater the catalytic effect of chemical reactions | | | | or the extent of exposure is long, unpleasant and |
| in wine. | | | | off-putting aromas and flavors can develop. |
| Of concern in wine are visible light and the sun's | | | | Specifically, red wine has sulfur-containing amino |
| UVA rays-yes, UVA rays because research has | | | | acids, namely, containing methionine and cysteine, |
| proven that even a short exposure of wine to | | | | which have a thiol (sulfur-hydrogen) side chain in |
| sun (UVB and UVC are absorbed by the | | | | their structures. These then react with naturally |
| atmosphere), in the order of hours, can have | | | | occurring vitamins, such as riboflavin (vitamin B2) |
| detrimental effects. That's because UVA rays lie | | | | and pantothenic acid (vitamin B5)-water-soluble |
| in the 315-400 nanometer (nm) range of the | | | | vitamins that are easily destroyed by heat, |
| electromagnetic spectrum and therefore has | | | | oxygen and, that's right, UV light. The products of |
| more energy than visible light, which lies in the | | | | this reaction are sulfur compounds such as |
| 400-700 nm range. | | | | hydrogen sulfide, dimethyl sulfide (DMS), and |
| Glass acts as a filter, but clear glass offers no | | | | dimethyl disulfide (DMDS), responsible for imparting |
| protection against UVA and visible light. Green | | | | a range of foul smells from rotten eggs to |
| glass offers some protection, but only half as | | | | cabbage and wet dog. |
| good as amber; dark-amber glass offers almost | | | | Interesting science. |
| complete protection. So why is so much wine, | | | | And now I'm left to wonder if my precious |
| particularly many of the ultra-premium wines of | | | | magnum of 1991 Château d'Yquem, in a |
| the world, packaged in green glass? This is likely | | | | clear-glass bottle, which I bought for my son born |
| for historical reasons when making green-colored | | | | that same year, was affected by X-rays on its |
| glass was easiest and the effect of radiation on | | | | travel from the U.S. It was pre-9/11, however, |
| wine was unknown. | | | | the unyielding airport security guard simply couldn't |
| But glass is only half the story. We must now | | | | be convinced not to X-ray my precious bottle. I |
| consider the optical properties of wine to then | | | | guess he was not a fine-wine aficionado. |
| determine how radiation effects any chemical | | | | |