Degassing is a complex process, and one at the heart of efficient wine kit production. Unless you can ensure that carbon dioxide generated by fermentation has been removed from the wine can alter the flavour and mouth feel.
Vigorous stirring (using a drill-mounted wine-whip, I hope!) and careful attention to proper fermentation times and temperatures are the keys to effective degassing, but how can you actually tell if you’ve gotten all the gas? Sometimes stirring and generate a lot of foam in a wine, and telling the difference between foam and fizz isn’t always easy.
The best way to check for remaining gas is to do a “puff” test. Fill a hydrometer jar about half-way with a sample of the wine being degassed. Very carefully cover the top of the hydrometer jar with the palm of your hand, pressing lightly to seal it, and give it several, sharp shakes. Slowly release your palm from the top of the jar while simultaneously listening for a “puff” of escaping gas and checking for the sensation of released pressure against the palm.
That’s all there is to it, except for discarding the wine afterwards (it’s less than 100 ml, so unless you can guarantee that you’ve got sterile plams, don’t pour it back in the carboy). Article from Tim Vandergrift, Technical Services Manager, Winexpert Inc.