Frederick, Joanne and All,

There may be some confusion about molecular sulfur dioxide levels and
the microbial stability of wine.

When sulfur dioxide is added to wine, some sulfur dioxide combines with
other materials in the wine and becomes bound or "fixed." The remaining
sulfur dioxide is in the "free" form. The free sulfur dioxide exists in
three different forms, the molecular form, the bisulfite form and the doubly
ionized sulfite form. In general, only the molecular sulfur dioxide is
effective against wine microbes, and many winemakers try and maintain a
level of 0.8 milligrams of _molecular_ SO2 per liter of wine. But, the
fraction of free sulfur dioxide that exists in the molecular form is
strongly dependent upon the pH of the wine. Consequently, winemakers are
always interested in wine pH so they can tell how much of the SO2 exists in
the molecular form.

Unfortunately, many wine microbes can tolerate much higher levels of SO2.
Some yeast strains, such as Saccharomyces bailii, can maintain normal
fermentation rates when more than 200 ppm of SO2 are present (see Rankine,
Making Good Wine, page 286). Vinegar bacteria are not very sensitive to
SO2. "Sulfur dioxide has almost no effect on the acetic acid bacteria
growth in the regular concentrations of SO2 in wine" (from Margalit,
Concepts in Wine Chemistry, page 327).

So, the value of 0.8 milligrams of molecular SO2 per liter of wine is only a
generalization and maintaining this level of SO2 certainly does _not_
guaranty microbial stability of any wine. In fact, the value of 0.8 mg/l is
really only applicable to some of the lactic bacteria and some native
yeasts.

Regards,
lum

"frederick ploegman" > wrote in message
...
> Hi Rick
>
> Please see my comments to Mark (above in this thread). Further
> comments interspersed.......
>
> "Rick Vanderwal" > wrote in message
> ...
> > by the sounds of it, you should do that before adding the yeast....
> > I just started a batch and wasn't aware of the ph factor...
>
> Let me try to explain some aspects of acid management. TA is
> merely an empirically established *guideline*. Very helpful but
> certainly not critical to success. OTOH - pH *is* critical to
> success because it determines if the wine will have microbial
> stability. This is why Joanne has stressed the importance of pH
> in the other thread. While a pH meter is certainly the preferred
> way to check pH, the papers you have are perfectly adequate for
> doing this if you don't want to spend the money for a meter (they
> ain't cheap).
>
> > and now my acid is a bit too high...
>
> See my comments to Mark on acid reduction.
>
> > so now I have to wait and perhaps cold stabilize after fermentation is
> > all done...
>
> As Ben mentioned in the other thread, you will receive no benefit
> by cold stabilizing this wine. "Tartaric" wines *must* be cold
stabilized.
> "Non-tartaric" wines (which your wine is) cannot form bitartrate
> crystals because there is no tartaric acid present to combine with
> the potassium. The reason that wines are categorized as "tartaric"
> or "non-tartaric" is because acid management is radically different
> for these two types. The above is just one aspect of this.
> HTMS
>
> > or later add potassium or calcium carbonate...
> >
> > I would do it before adding the sugar....
> > before fermentation...
> > Rick
> >
> >
> >
> > "MkFn" > wrote in message
> > om...
> > > I'm about to start my first batch of raspberry wine and have purchased
> > > a Wine Acid Test Kit.
> > >
> > > When do I test the acid, before or after I add sugar?
> > >
> > > Are the guidelines for starting a must?
> > > For example should I add sugar first, then test/adjust for acid before
> > > adding the yeast?
> > >
> > > Is there a specific order?
> > >
> > > thanks,
> > > Mark
> >
> >
>
>