"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