Acid test
 

What would be easier to use and more accurate. A titration kit with a PH
meter or a Acidometer? I don't get the titration kit by itself. I add tons
of acid and the color of the wine still changes with only 1cc of sodium
hydroxide.

Acid test
 

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

Acid test
 

Acid test
 

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)

Acid test
 

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)
>

Acid test
 

Stop at the permanent color change.

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,

The Europeans use 7 as the endpoint, North Americans use 8.2. I have
noted it's not that big a difference just as Greg mentioned, the PH
really takes off around 7. I use 8.2


> > 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.
>

....> 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).

Acid test
 

I just purchased a PH meter. I got a Hanna Piccolo 2. No more guessing
games for me.




"Joe Sallustio" > wrote in message
om...
> Stop at the permanent color change.
>
> 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,
>
> The Europeans use 7 as the endpoint, North Americans use 8.2. I have
> noted it's not that big a difference just as Greg mentioned, the PH
> really takes off around 7. I use 8.2
>
>
> > > 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.
> >
>
> ...> 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).

Acid test
 

Thanks for those insights everyone. I can see it's high time to buy a pH meter.

Jim

Acid test
 

The equivalence point (amount of acid = amount of sodium hydroxyde)
depends on the acids present and their relative amounts. For tartaric
acid it will be at about pH=8,5. For malic acid it would be about
pH=9,8. In a mixture of acids (wine) it will be very difficult to even
find the exact equivalence point even if you obtained the full
titration curve, but such a curve will give the best indication.
To simplify this a titration standard is used. The exact pH value does
not become very important as long as it is in the range 7 - 9. The
selected value of pH=8.2 Is probably a practical choice since the
commonly used indicator phenolptalein starts its colour shift to red
at this point.
Why the Europeans selected pH=7 is perhaps because this represent the
value for pure water. Strictly all titrations require a correction for
the titration error made by using an indicator with colour change at a
different pH than the "equivalence" point of the acid(s). For the US
standard this error is negligible when using phenoltalein.

Greg Cook > wrote in message ws.com>...
> On 3/25/04 5:24 PM, in article
> , "Joe Sallustio"
> > wrote:
>
> > Stop at the permanent color change.
> >
> > 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,
> >
> > The Europeans use 7 as the endpoint, North Americans use 8.2. I have
> > noted it's not that big a difference just as Greg mentioned, the PH
> > really takes off around 7. I use 8.2
>
> Yup - I suspect that is because the European standard for TA is based on
> Sulfuric Acid (H2SO4) rather than Tartaric Acid. Can anyone enlighten me on
> that one?
>
> Thanks.

Acid test
 

Greg Cook > wrote:

> 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).

Theoretically, that's true and I always assumed there'd be little
difference. I haven't done enough comparisons to accurately judge, but
I actually just read a paper recently which suggests this difference
*is* significant.

In the paper [1], they compared the OIV method (titrate to pH 7.0, 50
ml wine) and the AOAC method (titrate to pH 8.2, 10 ml wine diluted
with water to 100 ml) for 30 wines. They found no significant
difference due to operative technique (i.e. the dilution and sample
sizes), but they did find a difference due to pH end-point. This
difference correlated to a TA difference of 0.6 g/l (as tartaric) for
reds and 0.5 g/l for whites. Well, I consider that significant.

BTW, if the standard was to titrate to the actual equivalence point
for wines, we'd all be titrating to pH's of around 10. In the purely
practical sense, I'm glad we have a standard at pH 7/8.2. Certainly
saves on the NaOH ;-)

Ben

[1] Darias-Martín, J. et al. (2003). Comparative study of methods for
determination of titrable acidity in wine. J. Food Composition and
Analysis 16, 555-562.

Acid test
 

On 3/29/04 6:35 PM, in article
, "Ben Rotter"
> wrote:

> Greg Cook > wrote:
>
>> 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).
>
> Theoretically, that's true and I always assumed there'd be little
> difference. I haven't done enough comparisons to accurately judge, but
> I actually just read a paper recently which suggests this difference
> *is* significant.
>
> In the paper [1], they compared the OIV method (titrate to pH 7.0, 50
> ml wine) and the AOAC method (titrate to pH 8.2, 10 ml wine diluted
> with water to 100 ml) for 30 wines. They found no significant
> difference due to operative technique (i.e. the dilution and sample
> sizes), but they did find a difference due to pH end-point. This
> difference correlated to a TA difference of 0.6 g/l (as tartaric) for
> reds and 0.5 g/l for whites. Well, I consider that significant.
>
> BTW, if the standard was to titrate to the actual equivalence point
> for wines, we'd all be titrating to pH's of around 10. In the purely
> practical sense, I'm glad we have a standard at pH 7/8.2. Certainly
> saves on the NaOH ;-)
>
> Ben
>
> [1] Darias-Martín, J. et al. (2003). Comparative study of methods for
> determination of titrable acidity in wine. J. Food Composition and
> Analysis 16, 555-562.


Ben --- thanks for the reference. This is very interesting.

--
Greg Cook
http://homepage.mac.com/gregcook/Wine

(remove spamblocker from my email)

Acid test
 

Something in the post and messenger for you?
"Ben Rotter" > wrote in message
om...
| Greg Cook > wrote:
|
| > 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).
|
| Theoretically, that's true and I always assumed there'd be little
| difference. I haven't done enough comparisons to accurately judge, but
| I actually just read a paper recently which suggests this difference
| *is* significant.
|
| In the paper [1], they compared the OIV method (titrate to pH 7.0, 50
| ml wine) and the AOAC method (titrate to pH 8.2, 10 ml wine diluted
| with water to 100 ml) for 30 wines. They found no significant
| difference due to operative technique (i.e. the dilution and sample
| sizes), but they did find a difference due to pH end-point. This
| difference correlated to a TA difference of 0.6 g/l (as tartaric) for
| reds and 0.5 g/l for whites. Well, I consider that significant.
|
| BTW, if the standard was to titrate to the actual equivalence point
| for wines, we'd all be titrating to pH's of around 10. In the purely
| practical sense, I'm glad we have a standard at pH 7/8.2. Certainly
| saves on the NaOH ;-)
|
| Ben
|
| [1] Darias-Martín, J. et al. (2003). Comparative study of methods for
| determination of titrable acidity in wine. J. Food Composition and
| Analysis 16, 555-562.