It is this time of year where you can sit outside in the evenings to hang out with friends. Throughout this time many bottles of wine are shared and enjoyed. During such an evening with several bottles of red wine, me and some friends noticed that the taste of one particular red wine became better the later the evening got. This was not because we were getting more and more drunk, but rather due to a process called ”breathing” or ”aeration”.

Breathing refers to chemical reactions taking place between the wine and the oxygen in air that start once the bottle is opened. Generally, two processes occur during breathing, these are evaporation and oxidation which cause the wine to release new aromas and flavors.

Evaporation is the transition from the liquid to the gas phase and some volatile compounds easily evaporate in contact with air. Examples are sulphur containing substances formed by sulphites in the wine. Sulphites are added to wine to protect it from bacteria. The second process, oxidation, is in this case the reaction of wine compounds with the oxygen in air, a similar process to the rusting of iron  (where iron reacts with the oxygen in air). Substances in wine sensitive to oxidation are various poly-aromatic compounds like catechins and anthocyanins. They are the flavor-rich, dark pigment molecules that give red whine its color.

It is worth mentioning that the production of flavor-rich, dark pigment molecules like anthocyanins and other poly-aromatic compounds in grapes stops at temperatures that remain constantly around 30 degrees Celsuis. This leads to a decrease of flavor-rich compounds and is one of many reasons why climate change is threatening to ruin the global wine production.

Additionally, ethanol, in other words alcohol, is sensitive to oxidation as well if a wine bottle is opened too long, for example over several days. During the oxidation of alcohol acetaldehyde and acetic acid are formed. Acetic acid is the main compound in vinegar and the reason wine turns sour after having been opened too long.

The last example shows that unlimited breathing is not good for wine either. In addition, not all wines benefit from breathing. Especially, older wines can deteriorate very quickly when in contact with air. Young, red wines, on the other hand, like the one my friends and me had, benefit a lot from breathing. White wines normally lack the dark pigment molecules that change during oxidation. For this reason breathing does mostly not alter the taste or white wines.

So, how long do you need to let a red wine breathe? Generally, you should taste a wine before deciding if it needs breathing at all. As bottle necks are quite narrow, they do not provide a lot of contact with air and the wine will need at least 30 to 60 minutes to breathe on its own. However, there are ways to speed up the process. For example, you could pour the wine into a decanter, a vessel with a neck for pouring and a very broad bottle body to provide a large surface area for the wine to breathe. You could also pour the wine back and forth between two vessels or just swirl your glass before drinking the wine.

I hope the weather is nice were you are, so you can enjoy a glass outside with friends tonight.