Degassing with a vacuum pump

I just got a medical grade vacuum pump off ebay and am amazed at how many bubbles I am getting during degassing. I have some questions:

The batch I just finished was at its degassing step, I had already used a whip on drill a few days ago, but put it on the pump. I am using an orange carboy cap with one port capped and a tube running to the pump. The gauge is showing 21 and 525 depending on the scale (not sure what that means). I pumped it for about 3 hours last night, getting bubbles all the time and finally called an end to it. Is that too much? Does it help to keep pumping until no bubbles.

Another question: I just took a batch that is a couple of days from bottling and put it on the pump. It's getting a lot of bubbles. Am I damaging the clarity or helping by getting out more co2? Is it pumping out oxygen too?

Thanks in advance for any help I can get!

I just don't know! Normally, you degas until you don't need to degas any more. But it's also easier if the wine is warmer- the warmer liquid releases co2 better- and the last two wines I bottled this winter just seemed to never want to stop!

A good way to check would be to pull out a small sample and put it in a glass. Put your hand over the glass, and shake. Remove your hand. (Oh, do this over the sink, BTW!). If the wine is flat, you're done degassing. If not, degas some more.

Be sure that the vessel you are pulling a vacuum on is capable of handling negative pressure. If not, you could have a very messy implosion!

Sounds like you might be pulling atmosphere into the carboy and then expelling it in the form of bubbles coming out. I've whipped my wine in the carboy for a total of 10 minutes and it was done. Three hours pumping seems excessive.

samc said:

Sounds like you might be pulling atmosphere into the carboy and then expelling it in the form of bubbles coming.

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I'm not sure how that would happen.

+1 to checking pressure ratings. Or do it in a tub and be ok with maybe losing a batch of wine.

did the volume decrease??? The reason I ask is you can get water to boil at room temperature by creating a vacuum above it so maybe what you were pulling out was water vapor.

Daze said:

did the volume decrease??? The reason I ask is you can get water to boil at room temperature by creating a vacuum above it so maybe what you were pulling out was water vapor.

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This is very true. I'm an HVAC tech and I work on lithium bromide absorption chillers where water is used as the refrigerant. Under sufficient vacuum (5mm Hg) the water boils at 40˚F.

actually I got to thinking about it, it is more likely to be alcohol vapor rather than water vapor as the alcohol will be the first liquid component to break the surface tension.

Daze said:

actually I got to thinking about it, it is more likely to be alcohol vapor rather than water vapor as the alcohol will be the first liquid component to break the surface tension.

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Interesting that you mention that, as we add octyl alcohol to the refrigerant (water) as a wetting agent to reduce the surface tension of the water so that it has a better surface contact with the copper tubes in the heat exchanger. Adding the alcohol increases the efficiency of the chiller by as much as 15%

The gauge is showing 21 and 525 depending on the scale (not sure what that means).

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21 is inches of mercury, 525 is millibars.

There are 29.92" in a standard atmosphere of pressure. Pulling 22" is about as good as most of these pumps will pull.

I generally go with 20"+ for about 20 min. Too much vacuum can remove flavors nd aromas from your wine.

Thanks for all your comments!

I think all I was doing was overstressing my new pump. I going to try racking the wine in a vacuum to degass, that seems to be a good technique.