As you know, the fermentation process (both the initial fermentation turning sugar into ethanol and the secondary malolactic fermentation) produces quite a lot of carbon dioxide gas. The majority of this escapes from the wine’s surface during and immediately after the fermentation itself, but quite a lot will be dissolved into the wine and will be retained in solution. Over time, most of the gas will naturally evolve out of the wine but depending on the storage temperature, age of the wine, and the wine’s individual chemistry, sometimes there’s more CO2 left than we desire.
Higher than desired levels of carbon dioxide gas can contribute to a sense of “hardness” and can make a wine taste overly acidic and even fizzy or spritzy if levels are too high. Often a winemaker will want to adjust the level of CO2 as a wine approaches bottling. Too little carbon dioxide, especially in white wines, can leave the wine feeling flat and flabby in the mouth. Too much, however, can make a smooth Chardonnay taste not like itself at all. Wines will naturally degas themselves with time, racking, and especially during time spent in barrel.
However, so many times we’ve got a white wine that we may want to bottle young, as you mention, or have to accelerate a wine along the way . . . small-scale folks degas, especially if the wine is very spritzy and young, by using a tool like the “Wine Whip” from Fermtech. It’s a slightly-angled plastic rod that fits on the end of a standard power drill and is inserted into the barrel or carboy and turned on briefly, ‘whipping’ up the wine and stirring up any carbon dioxide bubbles, underneath the surface of the wine. An alternative for home winemakers is to buy a purpose-built vacuum pump degassing system, usually sold with various stoppers and adapters for different fermenters. A simpler and less-invasive approach (especially good if the carbon dioxide levels are not too high in your wine) is just to rack from one container to another, or moving the contents from one container to another with a siphon hose. With either method, it’s really important to protect the wine from surface oxygen, especially if white, with a layer of argon gas as you go from one to the other. We don’t want any oxidation!
Commercial wineries with tanks far too large for a Wine Whip do it a couple of different ways, often involving sparging stones, nitrogen cylinders (which helps strip CO2 from wine), and pumps. (Take note — if you stuck a mixer into a tank with a lot of dissolved CO2, you’d blow the top off. There are some pretty spectacular videos on YouTube showing just that!) During cellar movements, like when going from tank to tank with a pump and hose setup, a winery will install a sparging stone (somewhat like those used to diffuse air into a fish tank, just much bigger and stronger) on the outlet side of the pump and meter in a gentle flow of nitrogen gas. As the wine passes by the nitrogen gas and sparging stone, the nitrogen will help the carbon dioxide come out of solution, and then the wine in the end tank will have less CO2 — both the nitrogen and CO2 will come out in the tank’s headspace.
It’s really hard to dissolve CO2 in a wine’s headspace back into a wine — though it will happen if the wine is cold enough and there’s enough time involved. I tell my home winemaker friends their best degassing bet is just plain old bulk storage in their barrels and carboys — the wine will naturally off-gas during the aging process. Time is your friend! Leave the whips for the cream and egg whites.