Too Early Mead Stabilization?

[jayich]

I just racked a melomel into a 3 gal tertiary carboy with additional oak. I stabilized it with 0.7gm sulfite and 2gm sorbate. Since I plan to age this melomel at least 2 more months, I am now wondering if I should not have stabilized it since by the time of possible backsweetening, SO2 may have evaporated thru the airlock and I don't know how long the sorbate is good for.
Will I need to stabilize again if I decide to backsweeten in several months?

 

[Medsen Fey]

If you will post the recipe details, folks can provide you more insight. We need to know alcohol level and pH and can you tell us if the mead was clear?

The sulfite will gradually disappear over time, but it will last form many months under airlock. However the dose you used (700 mg in 3 gallons) works out to about 35 PPM total SO2 (if I did my math right), and that isn't very much. You will likely need more before bottling to insure stability.

The sorbate does not go away and only slowly binds with other things over time. The dose you added works out to be about 130 ppm Sorbic Acid (74% of sorbate by weight), which is in the middle range, and may need to be higher.

 

[jayich]

Thanks Medsen. The pH was 3.25 and the ABV was about 13%. Your 35ppm figure is correct for ppm of total SO2- I made the mistake of calculating ppm for Kmetabisulfite(the whole molecule) to be 61.7 but I forgot that total SO2 would be 57% of that amount(35 ppm). I know that free SO2 increases with decreasing pH but I don't remember the link you previously provided that had a chart from which you could estimate free SO2 base upon pH- do you remember that link so I could print it out and not bother you again? Oh yes, the mead was very clear.

 

[Medsen Fey]

I don't recall which chart was posted before, but the one below has the info.

 

[jayich]

Thanks for the chart Medsen. I seem to remember free SO2 increasing with decreasing pH which is the opposite of what the chart seems to indicate. The article that you posted also talked about levels of free SO2 needed to kill bacteria. I thought I saved the article but I will search the site for it since I want to reread it.

 

[Medsen Fey]

The goal of using sulfite is to have a MOLECULAR SO2 level that is adequate to keep bacteria, yeast, and spoilage organisms suppressed. SO2 exists in 3 forms, the SO2, sulfite and bisulphite. The Molecular SO2 form is the most active form (by far), and the percentage in each state depends on the amount of Free SO2, and the pH. What the chart is showing is how much free SO2 you need at each pH level to achieve a target of 0.8 or 0.5 ppm Molecular SO2. I'd shoot for the 0.8 ppm in most cases (the pink curve).

Now if you have added 35 ppm total SO2, you can figure about half has been bound (at least), so your free SO2 is probably no more than about 17 ppm. You can measure this with a test kit in most cases to determine what your free SO2 is so you don't have to guess.

At a pH of 3.25, you need at least 23 ppm free SO2 to have the Molecular SO2 at 0.8 ppm (the pink curve). So my guess would be that you need to add at least 12 ppm more total sulfite to get to that level. A bit more won't hurt to give you a little safety margin.

Check the links in the thorough explanation of sulfite thread in the patron's area for your reading pleasure.

 

[jayich]

Thanks for the links and discussion of a complicated area. Many years ago I was a chemist but now I have to really concentrate to make these concepts sink in! I will read the articles carefully.
Steve