Investigation of molecular changes in wine during storage in refrigerated cabinets
Authors: Renner Hannah , Richling Elke , Durner Dominik 
Published: June 2023

Wine is a complex chemical mixture that is bound to change over time. Most wines are produced for consumption within months. Some premium wines are meant to be maturated for several years or even decades after bottling. The post‐bottling evolution and the longevity of a wine depends on its initial chemical composition and the storage conditions. Temperature, exposure to light and the closure type are often mentioned as the most important storage influences. Especially elevated temperature is known to cause accelerated aging reactions in wine. Refrigerated wine storage cabinets promise to be the best storage option without the need of a wine cellar. They are available in different sizes and fit in every household. However, the influence of vibrations and low‐interval temperature fluctuations caused by compressors are parameters that have been neglected in literature. The aim of this thesis was to investigate if vibrations and low‐interval temperature fluctuations, which occur in refrigerated wine storage cabinets, have an influence on the post‐bottling evolution of a wine. The influence of both parameters was studied separately from each other.The impact of vibration on oxidation and gas uptake from the headspace of a wine bottle into the wine was investigated using a model wine with saturated O2 and different headspace volumes. The study revealed that vibration promotes the dissolution of O2 from the headspace of bottle into the wine resulting in a faster SO2 consumption. Furthermore, it was shown that horizontal bottle position accelerated the O2 uptake significantly. It was concluded that the increased surface size between headspace and wine accelerates the O2 dissolution in wine. Also, bigger headspace volumes caused an accelerated O2 uptake into the wine. An experiment without any headspace volume revealed that the factors vibration and bottle position did not accelerate the O2 consumption in wine. This proves that vibration and bottle position accelerate only the dissolution of O2 in wine, but not the chemical reaction of O2 with wine constituents.The influence of vibration on the volatile profile of wine was investigated using Riesling sparkling and still wines sealed with different closures that were subjected to vibration for six months. Vibration caused no CO2 losses, SO2 and color changes in all wines indicating that vibration caused by compressors has no impact on the gas permeability of the used closures. However, vibration affected the volatile profile of sparkling wine and Riesling still wine sealed with a screw cap. Similar to the model wine study described earlier, it was shown that the equilibrium of volatile substances between the wine and the headspace in a bottle was influenced by vibration. The gas‐liquid‐equilibrium of some volatile compounds was shifted towards wine, while others were shifted towards headspace. As a result of this, the concentration of volatile compounds in wine is changed. Besides this indirect influence of vibration, the results of this study also suggested that specific degradation and formation reactions of volatile compounds are directly influenced by vibration. These multiple effects of vibration most likely explain why increasing vibration intensities could not be proportionally related to the observed volatile changes. The investigation of different wine styles revealed that the impact of vibration depends strongly on the initial composition of wine, age, and packaging conditions. Especially, headspace volume, closure type and CO2 pressure are likely to influence the equilibrium of volatile substances between the wine and the headspace in a bottle.Another study investigated the impact of low‐interval temperature fluctuations on the volatile profile of wine. For this purpose, a Riesling wine was stored for two years under different temperature fluctuation patterns caused by compressors. Additionally, a model wine with nine volatile substances with known concentrations was stored for eight months under the same fluctuation patterns. The low‐ interval temperature fluctuations were compared to the mean value of the temperature fluctuations. Chemical and sensory analysis revealed that that low‐interval temperature fluctuations accelerate wine aging reactions like ester hydrolysis and monoterpene degradation. Even small temperature amplitudes showed a significant impact on wine aging. The observed effect was explained by the Arrhenius equation which states that reaction rates exponentially increase with rising temperatures. A pump effect of air through the closure was initially assumed but not observed in this study. Small deviations in wine temperature, such as those caused by door openings of a refrigerator were found to be negligible. It was concluded that low‐interval temperature fluctuations can accelerate wine aging reactions. The amplitude of the temperature fluctuations should be as small as possible during bottle storage of wine.This thesis showed that both parameters, vibration, and low‐interval temperature fluctuations, have been proven to influence the evolution of wine during bottle storage. Regarding storage conditions in a refrigerated wine storage cabinet, those parameters should be monitored. Wine connoisseurs should therefore consider good wine cabinets, since some manufacturers emphasize on the importance to minimize vibrations and temperature fluctuations in their devices. The development of technology should be advanced to reduce both vibration and temperature fluctuations in refrigerated wine storage cabinets. Future research should focus on specific wine compounds in model systems and realistic vibration conditions to reveal the relationship between vibration intensities and reaction rates. The impact of low‐interval temperature fluctuations on wine compositional changes should be investigated considering horizontal and vertical bottle positions. The calculated acceleration factors due to temperature fluctuations have to be verified by isotherm storage conditions at higher temperatures.