"pp" > wrote in message
om...
> Hi:
>
> I've been having a pretty consistent problem with titrating white
> juice before fermentation, adding tartaric acid based on the results,
> and then titrating after fermentation that the TA level is way too
> high. Latest example: Pinot Blanc juice measured at 4g/L, acid added
> to raise to 6.5g/L, now measured at 8g/L after relatively cold (around
> 15C) fermentation. I really don't know what's going on because:
> - I'm using the same method (pH meter to 8.2) before and after
> fermentation;
> - the juice is fresh, so all acid should be measurable before
> fermentation;
> - it can't be sodium hydroxide losing strength because then the
> measurement would be artificially higher, not lower;
> - the error seems to be consistent, so that cancels any possible
> accidents, like wrong sample size.
>
> I'm stumped at this point, and I'd really appreciate any help on this,
> as I don't enjoy wines that are too heavy on acid.
>
> Thx,
>
> Pp

Hi Pp,
You may not have a measurement error. Acid adjusted, grape fermentations
often measure from 0.5 to 1.5 g/l higher after fermentation because yeast
produces succinic acid during fermentation. If you chill the wine to 32
degrees or so for a few days, potassium bitartrate will precipitate out of
the wine and reduce the titratable acid. Sometimes, the drop in TA due to
tartrate precipitation is about equal to the increase in from succinic acid,
and the TA of the cold stabilized wine ends up being just about equal to the
starting TA. See Margalit, Concepts in Wine Chemistry, page 17.
lum

"Lum" > wrote in message >...
>
> Hi Pp,
> You may not have a measurement error. Acid adjusted, grape fermentations
> often measure from 0.5 to 1.5 g/l higher after fermentation because yeast
> produces succinic acid during fermentation. If you chill the wine to 32
> degrees or so for a few days, potassium bitartrate will precipitate out of
> the wine and reduce the titratable acid. Sometimes, the drop in TA due to
> tartrate precipitation is about equal to the increase in from succinic acid,
> and the TA of the cold stabilized wine ends up being just about equal to the
> starting TA. See Margalit, Concepts in Wine Chemistry, page 17.
> lum

Hi Lum:

Thanks a lot for this interesting info. I've always thought the acid
level is supposed to drop after fermentation by about 0.5g/L on avg.
So, if I understand this correctly, after cold fermentation, the acid
can actually move in any direction w.r.t to the starting level,
depending on the levels of succinic acid generated and bitartrate
falling out? And, does this only apply to juice that has had tartaric
acid added to it or in general?

I'll definitely check out the Margalit reference, only have to hunt it
down, which will take some time.

Thx,

Pp

"pp" > wrote in message
om...
> "Lum" > wrote in message
>...
> >
> > Hi Pp,
> > You may not have a measurement error. Acid adjusted, grape
fermentations
> > often measure from 0.5 to 1.5 g/l higher after fermentation because
yeast
> > produces succinic acid during fermentation. If you chill the wine to 32
> > degrees or so for a few days, potassium bitartrate will precipitate out
of
> > the wine and reduce the titratable acid. Sometimes, the drop in TA due
to
> > tartrate precipitation is about equal to the increase in from succinic
acid,
> > and the TA of the cold stabilized wine ends up being just about equal to
the
> > starting TA. See Margalit, Concepts in Wine Chemistry, page 17.
> > lum
>
> Hi Lum:
>
> Thanks a lot for this interesting info. I've always thought the acid
> level is supposed to drop after fermentation by about 0.5g/L on avg.
> So, if I understand this correctly, after cold fermentation, the acid
> can actually move in any direction w.r.t to the starting level,
> depending on the levels of succinic acid generated and bitartrate
> falling out?

Yes. TA can go up, down or stay the same, but not by large amounts (~1 g/l
or so).

>And, does this only apply to juice that has had tartaric
> acid added to it or in general?

Succinic acid production is not very dependent on the amount of tartaric
acid added, but tartrate precipitation will be greater with larger additions
of tartaric acid.

> I'll definitely check out the Margalit reference, only have to hunt it
> down, which will take some time.
>
> Thx,
>
> Pp