•The Food and Drug Administration cautions that there may be potential health problems for people with asthma. TTB regulations say any wine with a level greater than 10 mg/l must say “contains sulfites” on the label. The maximum level allowed is 350 mg/l. That is way above a level needed. Keep in mind that many yeast strains produce levels that exceed 10 ppm.

Two forms of SO2 will develop when added to wine. The two forms add up to “Total” SO2. 1.Bound (fixed). a.Doesn’t do as much to protect the wine but subtracts from the “helpful” amount. How much binds up is not the same from situation to situation. 2.Free SO2 (yes, you do have to pay for the “free” SO2 kit). a.It also divides into parts with the major ones being the molecular form and the bisulfite form. 1.The molecular form is the most important to the winemaker. It is the real microbe fighter. a.0.8 mg/l of molecular SO2 is considered the needed amount for white wine and 0.5 mg/l for red wine. b.Certain “free” SO2 levels are needed to insure the target amounts of molecular SO2 are maintained. 1.It’s important to note that the amount of “free SO2 to add to maintain the proper molecular level is dependent on the wine’s pH. 2.Another thing to note is that what is determined to be an appropriate amount of “free” SO2 added one day to maintain the desired molecular level may have that level go below the desired amount due to some of the SO2 becoming bound.

Hi

Indeed, SO2 can be reduced to H2S through the sulfate reduction pathway. But, my first question is how did you measure your total SO2 content? Some methods are less specific thatn others.

As mentioned by Moussa SO2 contains one fraction bound to aldehydes, (active on bacteria , but not on yeast) , and the "free fraction" that is also partitionned at wine pH between the molecular SO2 part which is active and and the ionized fraction which is less active. Of course the equilibrium between depends on the pH.

Such a concentration of 10-12 mg of total SO2, is rather low at the end at alcoholic fermentation (especially if you used a sulfited grape must) , and cannot be reduced as S. cerevisiae yeast will produce some SO2 for its metabolic needs.

I do not think that this is the cause of your problem , even if I am not a specialist of second fermentation. However did you check your wine after the first fermentation? The CO2 produced by the second fermentation enhance aromas release in glass headspace, and may be H2S and related compounds have been produced along the first fermentation.

Jean-Luc

no, 12 mg could not be the cause, because it is under the natural level of SO2 in a natural wine!

I think 12 mg/L is possible depending on the strain you've used for inoculation. The low H2S strain has a mutation that naturally produces higher levels of SO2/3

I think 12 mg/L is possible depending on the strain you've used for inoculation. The low H2S strain has a mutation that naturally produces higher levels of SO2/3