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

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