Wine Integrity

Wine integrity is probably the most important consideration to make when choosing between glass colors. One will need to choose between a clear bottle that displays the wine color or a dark bottle color that provides UV protection. Not only is wine sensitive to both sunlight and fluorescent light, but an hour of sunlight can change the flavor of a wine and produce off-flavors, which are sometimes called lightstruck flavors.

A photochemical reaction occurs in wine after exposure to light wavelengths between 350-500 nanometers (nm), and most damage happens when exposed to 370- 440 nm. Light wavelengths can pass through the glass of a wine bottle and stimulate the riboflavin that’s naturally present in wine. The wine contains about 0.4mg/liter of riboflavin; cysteine and methionine amino acids are present in wine at about 1-4 g/liter. Once riboflavin is stimulated, it reacts with the cysteine and methionine to form hydrogen sulphide and mercaptans or 3-methyl-2-butene-1-thiol (MBT). You want to avoid mercaptans because they have the unpleasant lightstruck flavors of rotting leaves, cooked cabbage, leek, onion, skunk, wet wool, soy etc. Since humans are flavor and aroma sensitive to mercaptans at about 4 ng/liter, these products are really overpowering, and winemakers try to minimize them by choosing colors of glass that offer different levels of UV protection.

Certain varieties of grape, certain wine styles, and wines that have more amino acids or hydrogen disulphide (H2S) are more at risk to develop off-flavors. Lees-aged sparkling wines may be more susceptible to developing lightstruck flavors because of the contribution from the lees and dead yeast cells. For this reason, sparkling wine is rarely bottled in clear glass. Since aromatic and neutral white wines are delicate, you can taste any off flavors more easily. A wine with a small amount of H2S in it at bottling can develop mercaptan in the bottle, too.