Quote from my latest wine kit "To determine if your wine is fully degassed, fill your hydrometer test jar halfway with wine and seal it with a bung or the palm of your (clean) hand. Shake the test jar vigorously while maintaining a tight seal. Stop and release the seal. If the jar releases pressure, or a "puff" of gas, you must continue to stir. Double check to make sure your wine is at 72-75 deg, or it will require much longer stirring. If the wine foams in the test jar, but does not release pressure, your degassing has succeeded."