Degassing with a 7cfm vacuum pump question

[Takuie]

Being in the HVAC field, I have a 7cfm vacuum pump and had seen and read a lot about using these to degas wine as well as the dangers. The question I have is that after letting mine run for almost an hour, I am still getting bubbles. My concern is if I keep degassing will I not be "boiling off" the alchohol at this point?

When I first started I got the tiny little bubbles, then after about 10 mins they got significantly larger. After nearly an hour, the bubbles were very large but still continuiosly bubbling up. I know that we use these in HVAC systems to not only remove oxygen from systems but to remove other non condensables from a system like moisture because under a vacuum, water boils off and is removed. So would this apply to the alchohol in wine as well?

Using my manifold gauge, I kept the vacuum pressure around 21-24. Should I keep going until I get zero bubbles?

 

[DoctorCAD]

According to this chart http://tables4ethanol.webs.com/boilingpoint.htm (assuming 29.92 = your zero point) at 21 inches mercury (vacuum), (29.92-21 = 8.92) alcohols boiling point is about 120 degrees F. and at 24 inches mercury (vacuum), (29.92-24 = 5.92) alcohols boiling point is about 110 degrees F.

To get down to room temp, you would need somewhere around 26.6 to 27.9 inches mercury (vacuum). Although the chart states that vacuum distillation occurs between 20.58 and 8.87, I'd bet that the amount is so small as to not even be detectable at room temperature.

 

[sour_grapes]

Wow, 7 cfm is a pretty large pump. I'll take a stab at some of your questions.

You certainly do NOT want to keep going until you get no bubbles at all. One thing to realize is that one of the later bubbles does not have as much gas in it as one of the earlier bubbles (due to the lower pressure). What I have taken to doing is to monitor the amount of gas exiting the pump. (I attached a hose to the outlet, and can roughly judge the rate of gas egress by putting the hose in a glass of water, for example.) The amount of gas coming out in these latter stages is quite small. Besides, your goal is not to remove all of the gas; your goal is to remove enough gas that your wine is not "gassy." A flat beer probably contains more CO2 than a glass of water does -- but it is still flat!

The issue of "boiling" the alcohol out is complicated. Yes, you can remove both water and alcohol by pumping on it. Pure alcohol has a vapor pressure of 45 mmHg at room temp, while pure water has a vapor pressure of 17 mmHg. You will preferentially remove alcohol from a solution of the two, but it is not so simple; the chemical interaction between the water and alcohol changes vapor pressure of the alcohol.

The procedure I find best is to have a half-empty carboy, pump on it, and then agitate (shake) it. This gets a lot of gas out quickly. After 15 or 20 min of this, I switch to the other half-empty carboy, and repeat. As I said, I monitor the exiting gas, so I have rough idea when to stop.

 

[Takuie]

Thank you both for your replies. Definitely helps