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Vacuum degassing and K-Meta

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Big Mac

Big Mac

NewBee
Registered Member
Jun 13, 2009
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I searched and haven't seen an answer to this. If one is going to vacuum degas using a hand-held vacuum pump, would that negatively affect the amount/effect of any potassium metabisulphite previously added? Should the degassing be done first? Thanks for any help.
 
I don't know of any quantitative studies that have been done on the effects of vacuum degassing on residual SO2 levels, but in principle I would think that some additional SO2 would be pulled out of solution when the pressure above the liquid was lowered. To be safe, you could get a sulfite test kit and measure it after the mead has been degassed, or treat with metabisulfite after degassing.
 
Thanks, Wayne. I'm gonna need to get a test kit, as I screwed up and tested the vacuum on a six gallon batch before knowing the answer to this question. The large amount of gas that came out of suspension made me suspicious that I was losing more than just CO2.
 
As a chemist / engineer and mead maker I do not see any reason the vacuuming will effect metabisulphite previously added. Yes it can remove the dissolved SO2 gas. But once the yeast has been inhibited by the SO2 they will not restart.
 
fjrussonc said:
As a chemist / engineer and mead maker I do not see any reason the vacuuming will effect metabisulphite previously added. Yes it can remove the dissolved SO2 gas. But once the yeast has been inhibited by the SO2 they will not restart.
Click to expand...

There are a number of reasons to add SO2 to a finished mead, and in fact "inhibiting" active yeast isn't generally one of them. While it will assist in keeping a fermentation from restarting once the yeast have finished on their own, adding K-meta to an actively fermenting must won't generally stop the yeast, unless you add so much as to be obvious (200 to 300 ppm or more are required to stop most strains of commercial wine yeast). SO2 is also a very effective antioxidant, and it will in addition keep spoilage organisms at bay. I believe that Big Mac is primarily concerned about reducing the concentration of free SO2 before any further racking and/or bottling, and in that case the amount of additional SO2 removed by vacuum degassing may be significant.

Admittedly that is an unsubstantiated concern on my part, lacking any quantitative evidence from controlled lab experiments to determine just how much is removed in a vacuum degassing operation. Still, unless you are equipped to measure sulfite in your mead, it is better to err on the side of caution. A little more than necessary won't hurt, and will eventually dissipate. Too little, and the effects that you are looking for may not manifest themselves.
 
Wayneb is exactly right. I was more concerned with retaining the antioxidant properties of the SO2 rather than stopping/retarding any further fermentation.
 
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