What is an inert gas? How and why are inert gases used in winemaking?
An inert gas is any gas that does not tend to chemically interact with other things. The main use of inert gas in the wine industry is to take up the space of (i.e. displace) other gasses that would do harm to the wine, namely oxygen. Oxygen accounts for roughly one fifth of our atmosphere and is fairly reactive. Everyone is familiar with the rust that forms when a piece of metal is left outside for a period of time. In this case, oxygen chemically alters (oxidizes) the iron in the metal to form iron oxide. Wine that is exposed to air will also succumb to the ravages of oxidation, albeit more quickly. Many compounds in wine react with oxygen, but primarily the (ethyl) alcohol is oxidized and forms acetaldehyde. The sensory result is that the fresh fruit aromas become diminished and are replaced with dull, nutty ones. Sherry and Madeira are examples of intentionally oxidized wines, so of course one can expect oxidized aromas when enjoying these styles of wine. However, it is our intention to create vibrant, exciting wines that have 100% of their natural fruitiness and freshness preserved. So, what kind of gases can we use to displace oxygen and protect our precious Epoch wine? Let’s look closer at the composition of the air we breathe:
Nitrogen (N2), 78.1%
Oxygen (O2), 20.9%
Argon (Ar), 0.9%
Carbon Dioxide (CO2), 0.03%
Other Trace Gasses, 0.07%
Wow, nitrogen makes up 78.1% of our atmosphere, and in the form of N2 (meaning two nitrogen atoms are bonded to each other), it is quite inert. Being so abundant, it is relatively cheap to distill from the atmosphere and is therefore inexpensive to buy. This makes nitrogen the wine industry standard for inert gas. There is one problem, however. The density of N2 is actually slightly less than that of air. Why would this be a problem? Think of a hot air balloon. The hot air in the balloon is less dense than the air surrounding it and therefore the balloon wants to rise up. While the difference in density between nitrogen and air is not enough to carry a balloon up into the sky, it does mean that the nitrogen will want to slowly escape your tank/bottle/barrel if given the chance. Air will inevitably creep in to replace it. It would be better if we had an inert gas that was heavier (more dense) than air so that it would want to sit down right on the surface of the wine.
CO2 gets a bad rap these days, but it’s not all bad! After all, plants need it to survive and our little yeast friends produce quite a bit of it during their fermentation of grape must into wine. In fact, it is this naturally produced CO2 that keeps the must fresh during fermentation until it is pressed and put to barrel. Besides carbon dioxide gas being a great oxygen displacer, solidified CO2 (dry ice) has the added benefit of being extremely cold. Winemakers like to use dry ice to chill down their fruit when it arrives in the cellar which simultaneously displaces oxygen from the must during that vulnerable period just after crushing when the fermentation has yet to begin. CO2 is heavier than air so it likes to stay put in your container, and it is relatively cheap being a common byproduct of other industries. Then why isn’t it used extensively in the cellar beyond the crush season? Crack open a soda or beer to find the answer. Yes, carbon dioxide readily dissolves into liquids imparting that familiar fizz that we love so much. This sounds great if you are making a sparkling Blanc de Blanc, but not so much for crafting a fine Tempranillo.
Here it is folks, the ultimate gas for the wine cellar. I hold a special place in my heart for argon and I get a little choked up just thinking about it. For starters it is a “noble gas.” Remember that term from chemistry class? The noble gases (including helium and neon) have exactly the right number of electrons to fill their electron shells. In other words, these gases already have everything they need to be complete, so they don’t feel the need to react with other substances. They are the enlightened yogis of the periodic table. As such, they are some of the least reactive substances known to man. Furthermore, argon is much heavier than air. When properly deposited in a partially filled container of wine, it makes a perfect invisible blanket of protection on the surface that can last indefinitely. Of course, there is a downside. Comprising less than 1% of the atmosphere, argon is much more expensive to produce than nitrogen. It costs more than double to buy, but in my opinion it is worth every penny.
Using Inert Gas
So what do we do with our beloved argon? Everything! Anytime we want to move wine from one vessel to another, we pre-fill the receiving vessel with argon, be it a tank, a barrel, or even the bottles on the bottling line. If we ever have to leave a tank or a barrel partially filled for any period of time, we make sure that it has a thick layer of argon protecting it from oxygen at all times. When we top our barrels, we use argon to supply the “bulldog” (see previous post regarding the use of the bulldog) which ensures that even our topping wine is protected, too.
I hope you can now appreciate the subtle role inert gases play in the making of your favorite Epoch wine, even though you can’t see, hear, touch, taste or even smell them. Cheers!