As anyone who has been around wine for very long knows, proper storage conditions for wine is very important in terms of maintaining wine quality. If a wine is exposed to too much light or too high of temperatures, off colors and aromas can be created in that bottle of wine, ultimately damaging the quality of the wine. Even when the bottles are made from â€śanti-UVâ€ť glass, as little as 450nm of radiation is all that is needed to induce changes in the color and aroma of wine when exposed to light.
Studies have shown that the color of the glass affects the color and aroma of the wine within when exposed to light; specifically it was found that green bottles have a greater protective effect against light than lighter colored bottles whenheld at a constant temperature. Interestingly, other studies have found the exact opposite, so itâ€™s not completely clear what is going on inside those bottles when exposed to light.
The goal of the study presented today was to examine further the influence of light and temperature on color development in white wine, and to potentially determine a mechanism behind these changes. In addition to the effect of light on wine color, this study also briefly examined how oxygen and the surface of the glass influenced oxidation in the bottle of wine.
Bag-in-box Chardonnay wine was used for this experiment and was enriched with 100mg/L of (+)-catechin.
750mL Claret punted style wine bottles were used and included the following colors: Flint, Arctic Blue, French Green, and Antique Green.
The wine bottles were filled with 740mL of the Chardonnay wine that was enriched with (+)-catechin. After filling, the headspace was flushed with nitrogen for 2 minutes to displace any oxygen present. Bottles were sealed with a screw cap and laid in a wine bottle holder at a angle such that all bottles were exposed to the same amount of light. The wine bottles were kept in light boxes (holding up to 8 bottles of wine each) for the experiments.
The source of light in the light boxes was a MegaRayÂ® mercury vapor, self-ballasted flood lamp (160 watts; High UVA and UVB). The light source was positioned 40 cm above the wine bottles. The light source was set to expose the bottles to light equivalent to full midday sun. Temperature of the air in the light box as well as temperature of the surface of the bottles was measured.
To keep the temperature constant (38 +/- 3 deg C) at the surface of the bottles, an exhaust fan was used in the light boxes. Air inside the light boxes was 30 +/- 2 deg C. Light was set to a timer of 16 hours on and 8 hours off, in order to simulate day and night time conditions. This 24 hour cycle was performed for 18 days with daily aerating of the bottles occurring.
Light absorbance was measured using a UV/Vis Spectrophotometer as well as liquid chromatography.
Dissolved oxygen and headspace oxygen were measured in the wine bottles.
To determine dissolved oxygen decay, oxygen sensors were placed in some bottles (Flint and Arctic Blue) prior to filling with wine and left overnight. Chardonnay was then added to the bottles to a level just above the sensor, was removed after 30 minutes and then filled to the top with Chardonnay leaving no head space. Dissolved oxygen was measured at 10 min intervals for 110 minutes, then 30 minute intervals up to 320 minutes. The final measurement was taken 16 hours after the experiment began. Temperature was also recorded during this experiment.
To determine ascorbic acid decay, 100mg/L of ascorbic acid was added to model wine and then this solution was added to Flint, Arctic Blue, French Green, and Antique Green wine bottles (both heavy and light weight) and stored in the dark at room temperature. Ascorbic acid concentrations were measured 4 times over 6 days.
Exposure to light using controlled temperatures:
â€˘ The temperature inside the light box was 30 +/-2 deg C and the bottle surface temperature reached up to 38 +/- 3 deg C.
â€˘ Control bottles (kept in the dark) showed no change in color pigmentation compared with treatment bottles (note: they were stored at 25 deg C).
â€˘ Color intensity after the light exposure decreased in the following order: Flint > Arctic Blue > French Green > Antique Green (i.e. Flint = greatest color intensity and Antique Green = least color intensity).
â€˘ Comparing heavy and light Antique Green bottles as well as heavy and light French Green bottles, no differences in color intensity of the wine was noted.
â€˘ Comparing heavy and light Arctic Blue bottles, the wine in the lighter weight bottles showed greater color intensity than the wine in heavier weight bottles (after the 18 day experiment).
â€˘ Wine in Flint bottles showed the greatest color intensity.
â€˘ Bottle weight was not as important as bottle color in terms of changes in color intensity of the wine.
o Bottle weight did not matter for the darker two bottles (Antique Green and French Green) though it did matter for the lighter two bottles (Arctic Blue and Flint).
â€˘ Exposure to light altered the aroma of the wines to include acetaldehyde, caramel, almond, quince, and acetic acid.
â€˘ Red and yellow pigments increased in wines in the following order: Antique Green < French Green < Arctic Blue < Flint (i.e. wines in the Antique Green bottles were the least red and yellow, while wines in the Flint bottles showed the most red and yellow pigments after the experiment was complete).
â€˘ Xanthylium levels were highest in wines in the heavier Flint bottles, and lowest in the wines in the Antique Green bottles.
o Xanthylium levels were higher in the wines in lighter Arctic Blue bottles compared with the wines in the heavier Arctic Blue bottles.
Exposure to light without temperature control
â€˘ (Note: this experiment lasted for 3 days instead of the 18 days of the previous experiment).
â€˘ Bottle surface temperatures reached up to 80 deg C during the 3 day experiment.
â€˘ Pigments changes were easily noticed after just 3 days.
â€˘ The greatest increase in color intensity was in the wines stored in the Antique Green bottles.
o Color intensity decreased in the following pattern: Antique Green > French Green > Arctic Blue > Flint (i.e. wines in Antique Green bottles had the highest color intensity while wines in the Flint bottles had the lowest color intensity).
â€˘ Xanthylium was not present in any of the wine samples.
â€˘ Aromatic changes to the wines included increases in acetaldehyde, honey, and kerosene aromas.
â€˘ Wines in the Antique Green bottles showed the greatest red and yellow pigment increases.
â€˘ When the light was switched on, the bottle surface temperature increased at the same rate for all bottles, though the high temperature for the Antique Green bottles was 5oC greater than the high temperature for the Flint bottles.
Influence of oxygen on pigmentation changes after light exposure
â€˘ (Note: this experiment utilized the Flint glass only).
â€˘ Bottles with low headspace decreased in dissolved oxygen to negligible amounts after 8 days, while bottles with high headspace first increased dissolved oxygen slightly then decreased to negligible levels after 13 days.
â€˘ For wines that were intentionally aerated throughout the experiment, headspace oxygen levels remained high and constant, while dissolved oxygen levels decreased to near negligible levels after 8 days.
â€˘ Wines intentionally aerated showed the greatest color pigmentation changes between days 10 and 17.
o The authors suggested that dissolved oxygen may play only a minor role in color pigment changes (i.e. perhaps simply initiation), as color intensity changed the most when dissolved oxygen levels were at their lowest.
â€˘ More catechin reacted in the aerated wines than the non-aerated wines.
â€˘ Xanthylium was only present in aerated wines.
â€˘ There was no effect of bottle color on the degradation of dissolved oxygen or in the oxidative loss of ascorbic acid in the experimental wines.
The results of this study were interesting in that they confirm the importance of storing wine at appropriate temperatures and under appropriate light conditions. While darker bottles showed less color change than lighter bottles when held at a constant ambient temperature of 30 deg C (38 deg C bottle surface temperature), comparing them with the control bottles left completely in the dark showed that even the darkest bottles do undergo some color changes when exposed to cycles of daylight.
If the bottles are not kept at a controlled temperature, however, and are just left out to fend for themselves in the sunlight during the day, it was interesting to see that the color intensity changes were the exact opposite as they were under controlled conditions. When temperature was held constant at 30 deg C (38 deg C bottle surface temperature), the darkest bottles (Antique Green) gave thegreatest protection against color intensity changes when exposed to 8 hours of light for 18 days, however, when temperature was not controlled, and it rocketed up to 80 deg C, the Antique Green bottles were the worst performers in terms of protecting the wine against color and aroma changes. I agree with the authors conclusions that this may be because the darker bottle absorbs and holds the heat for longer than the lighter bottles do, thus when exposed to extremely high temperatures, the darker the bottle the greater the color intensity changes.
In terms of the role of dissolved oxygen in color intensity changes of wine when exposed to light, I think a lot more work needs to be done. This study showed that dissolved oxygen may only play a minor role in color intensity changes of wine exposed to light, as color intensity seemed to change the most when dissolved oxygen levels were at its lowest. The initial results are certainly fascinating; however, I think more work needs to be done in this department.
I think the presence and absence of Xanthylium needs to be examined more, as these results were a little perplexing to me. Under temperature controlled conditions, Xanthylium levels were greatest in Flint colored bottles, whereas when temperature was not controlled, Xanthylium was not present. Finally, Xanthylium was only found to be present in aerated wines compared with non-aerated wines. What exactly does this mean? There may be some sort of interaction with dissolved oxygen, but itâ€™s not clear to me from the results and Iâ€™d be interested in seeing a separate study performed on this phenomenon.
Overall, I thought this was an interesting study and showed that temperature control is extremely important in terms of preserving the quality of your wines (at least with Chardonnay!–should be tested with more types of wine). Ideally, you should keep your wines under temperature control under complete darkness, but if thatâ€™s not possible, itâ€™s important to try and keep the wine bottle surface temperature from increasing too much, and to keep the wine away from direct sunlight for too long a period of time (Iâ€™m thinking the bottom of a dark closet if you donâ€™t have any way to control light or temperature otherwise).
In terms of bottle color, I canâ€™t really say which the ideal color is without knowing the storage conditions of that bottle. If you donâ€™t have temperature control, it may be better to use lighter colored bottles, as they wonâ€™t absorb and hold on to the heat as much as a darker bottle would. However, if you do have temperature control, a darker bottle would be best for protecting the wine against any light that may be exposed to the wine inside.
What do you all think of this study? Please feel free to leave comments or share your personal experiences!
Source: Dias, D.A., Clark, A.C., Smith, T.A., Ghiggino, K.I., and Scollary, G.R. 2013. Wine bottle colour and oxidative spoilage: Whole bottle light exposure experiments under controlled and uncontrolled temperature conditions. Food Chemistry 138: 2451: 2459.