I agree. When I did titration briefly in a commercial lab, I had my sample
on an automatic stirrer with a magnetic stir bar in the flask. Then, I added
phelphtptphptphptptptptliiiien :-) until the color lasted for about 5-10
seconds. Having the constant stirring helped make it uniform.
If possible, try to "get calibrated". Could you borrow a ph meter? Then
you could titrate and compare color to actual values until you calibrate
your pink (I loved calling it that).
Also, in my case, I had used a Cash Still to separate the volatile acids
out. The nice thing about this was that the condensed acidic liquid was
always colorless -- made "pinking" a lot easier.

Howard (newbie)


"Greg Cook" > wrote in message
s.com...
> On 3/25/04 8:50 AM, in article
> , "gus"
> > wrote:
>
> > (glad heart) wrote in message
> > . com>...
> >> Speaking of Acid Tritration, a great frustration for me is determining
> >> the end point when testing reds. Yes, I dilute the wine
> >> appropriately. Can someone please give me insight regarding the end
> >> point color I should be watching for? A red will gradually turn to a
> >> reddish-gray, then a more muddy red-gray, then brown-gray, then
> >> green-brown-gray, then dark green (I think the sequence is something
> >> like that) over a fairly large volume of NaOH additions.
> >>
> >> What color do I say "Eureka! It's neutral!"?
> >>
> >> Thanks, Jim
> >
> > hey jim,
> > i use a titration test and ph meter together.
> >
> > using a ph meter to check for the end point takes all the guess work
> > out of the end point. many on the board have said that the endpoint is
> > when you measure a ph of 8.2, however, my bottle of blueing solution
> > says to measure to 7.0 so that's what i do.
> >
> > good luck,
> > gus
>
>
> The thing to look for about titration using phenolphthalein is to stop at
> the point when adding a drop causes a pink color to remain even after
> swirling/mixing your sample well. If you go a few drops past, that's
> accurate enough for titration. Of course, this is pretty darn hard with
red
> wines - as you have noticed. Using a pH meter to titrate would be a
> preferred method with reds. Generally we titrate to pH 8.2 because that is
> the pH at which phenolphthalein changes color. Thus, it would be
consistent
> with colorimetric titrations. I think the difference between pH 7 and 8.2
> during the titration is a matter of just a few drops anyway (the titration
> curve is very very steep at the point of neutralization of the acids).
> --
> Greg Cook
> http://homepage.mac.com/gregcook/Wine
>
> (remove spamblocker from my email)
>