Free SO2 by Aeration / Oxidation

[Hazelemere]

I've been trying to ensure that I have enough free SO2 in my wine by following the recommendations here (1/4 tsp per 5-6 gallons every three months) and love Bryan's idea of dividing that amount by a third for monthly top-offs of barrels. Having watched a few presentations from Cornell on 'Preventing Spoilage Mechanisms' and 'Malolactic Fermentation Methods', and from watching the dialogue here, it seems like assessing free SO2 especially in barrels doesn't seem so difficult or expensive. That being said...

The process of assessing Free SO2 by Aeration / Oxidation seems pretty straight forward as described in several places online including this one by Enartis. There's also a video series on the MoreWine! website with their process.

There are also several videos on the internet, and one such video I found related that you didn't need to use the indicator solution of methyl red & bromothymol blue (although helpful) and that you could just use your pH meter and ensure you're starting and ending at the same number (he used 5.0). Using a pH meter would also reduce the chemicals needed, as wine would be below 5.0, brought up to 5.0 by a base solution, go through the aeration/oxidation process and then see how many ml of the base solution it would take to get back to 5.0. Has anyone assessed their free SO2 this way?

Follow up question, instead of using a vacuum to pull the vapors through the setup, or an air pump to push them through, could I use compressed oxygen delivered at the recommended 1L/min flow rate? I have a pretty good supply of compressed oxygen available to me. 10-15 minutes at 1 L/min is quite minimal.

Thank you much....

no oxygen. Won't work. If you want compressed gas use nitrogen

 

[David Violante]

My indicator solution came, I’ll have to rerun and try it with nitrogen, I do have some, just more availability of compressed oxygen. I’m curious to know the chemistry of why oxygen won’t work, completely out of personal understanding.

 

[Hazelemere]

My indicator solution came, I’ll have to rerun and try it with nitrogen, I do have some, just more availability of compressed oxygen. I’m curious to know the chemistry of why oxygen won’t work, completely out of personal understanding.

SO2 + H2O = H2SO3

2H2SO3 + O2 = 2H2SO4

2SO2 + 2H2O + O2 = 2H2SO4

 

[David Violante]

Hydrogen peroxide is H2O2 no?

SO2 + H2O2 = H2SO4

2SO2 + O2 = 2SO3

2SO3 + 2H2O2 = 2H2SO4 + O2

So would that be twice the amount being measured by using Oxygen versus air or nitrogen?

 

[Hazelemere]

Hydrogen peroxide is H2O2 no?

SO2 + H2O2 = H2SO4

2SO2 + O2 = 2SO3

2SO3 + 2H2O2 = 2H2SO4 + O2

So would that be twice the amount being measured by using Oxygen versus air or nitrogen?

only the oxygen that reacts with SO2. Not all of the available oxygen necessarily reacts. Nitrogen eliminates the oxygen reactions.

 

[Hazelemere]

Hydrogen peroxide is H2O2 no?

SO2 + H2O2 = H2SO4

2SO2 + O2 = 2SO3

2SO3 + 2H2O2 = 2H2SO4 + O2

So would that be twice the amount being measured by using Oxygen versus air or nitrogen?

No H2O2 is not H2O water

 

[ibglowin]

@David Violante

Do you have pure O2 or compressed air? The whole point of the aquarium pump is to"aerate" the sample and move the SO2 over to the peroxide "trap" where you then reduce the oxidized sample with NaOH using the indicator to detect the endpoint. I don't think it would matter if you use pure O2. After all the room air the aquarium pump (which is supplied with the More Wine Kit) is pushing through the sample has ~20% O2 in it so I don't see how using pure O2 would hurt an already oxidized sample.

 

[David Violante]

I do have pure O2 I’m using. I had most everything but the chemicals and so I was trying to set it all up as inexpensively as possible. I have compressed nitrogen as well. I will do an experiment with both to see if there’s any difference. Maybe not today though…

 

[rsportsman]

Why do AO at all? https://vinmetrica.com/product/vinmetricas-sc-100-sulfite-analyzer/

 

[ibglowin]

Why do AO at all? https://vinmetrica.com/product/vinmetricas-sc-100-sulfite-analyzer/

Cost jumps out immediately for one……

 

[David Violante]

Why do AO at all? https://vinmetrica.com/product/vinmetricas-sc-100-sulfite-analyzer/

I’ll happily use the vinmetrica if you’ll send me one! To Mike’s point, I have most of the items to do an AO and only needed the chemicals. So, cost is one factor. Since I’m not doing a bunch of these all day long, just doing it and seeing the process is another reason.