When I started using the vac pump did a little research. What I found was that ethanol vaporizes at 172 degrees F at sea level, at 25 in Hg it will vaporize at 79 degrees F. My wine is in the 64 - 66 degrees F range so no matter how long the degas process (at this temperature) the alcohol content should not be affected. At least that is the assumption I've been going on!
* A good assumption, you will not be able to measure a decrease in alcohol in solution , , , but if we had a university lab the actual decrease would be a few ppm.
GAS THEORY
* Water will dissolve 1.7 gram per liter of CO2 at 20C (room temp/ 1 atmosphere pressure) As the temperature decreases more CO2 will dissolve (roughly a log function) and as temp increases less will dissolve. As the CO2 comes out of solution it absorbes heat from the liquid which means that the solubility of the gas in your wine has increased ie the rate at which it comes out will decrease.
* We are pulling a vacuum which has the effect of increasing the rate at which the gas comes out, in this case it is linear to what is called the partial pressure. This is made up of the percent of CO2 in the headspace times the pressure in the headspace ie as bubbles start to come out the headspace will become enriched with CO2 and the rate decreases as we pull a gas out.
* The CO2 in the wine has reacted with water to create carbonic acid which reacts with the wine acids/ salts, drops the pH and technically is no longer a dissolved gas. All this works to come to equilibrium changing the chemistry as we try to degas our wine.
* As car-boy noted with his hardware / 25 inchesHg vacuum (0.16 atmosphere, ie 16% of normal pressure) it will take an hour to an hour and a half to get to the point where there isn’t an obvious release of gas bubbles. I am not surprised. All the equilibriums are being whacked out of balance and the 5 gallon mass will slow things down.
We have a fast way to do degassing when we vacuum transfer or a slow gentle way just by pulling a vacuum and even a more gentle way if we let it volitalize naturally at one atmosphere.
* All in all how anxious are we? , , The risk from racking/ transferring is that in the process we are exposing the wine to a new atmosphere which contains oxygen. This will follow the gas law like CO2 and some will dissolve. As with losing some alcohol we know it does happen , , but we probably wouldn’t be able to saturate the wine with oxygen, , just religiously added sulphites to take care of this, , and try to not over do the racking treatment.
