TA: Measurement & Thoughts...(Long)
SchlossGoist
Recently we have had a series of threads dealing with the measurement &
adjustment of Total Titratable Acidity (TA) of a wine must prior to
fermentation.
The following are a series of comments & observations regarding the TA
testing procedure in general, as well as some miscellaneous thoughts
regarding the manipulation of acid levels in an unfermented must:
1. A properly conditioned, cleaned, calibrated, and highly accurate pH meter
is essential to measuring the TA of the must/wine. Get a good pH meter &
throw your color change indicator away.
2. Use a large (30+ml) homogenous must/wine sample when testing the TA. If
the must is or has been fermenting, make sure to microwave the sample just
to a boil & to stir well before the titration.
3. Place your measured sample in a clear, glass container which allows for
easy swirling. A small wine glass is perfect.
4. Before starting a titration, make sure that your pH meter is conditioned,
cleaned, & calibrated. For more information on these procedures, see either
Joe Sallo's fine pH FAQ, or
http://www.eutechinst.com/techtips/tech-tips3.htm
5. Immerse the pH electrode in the sample. It will read the sample's pH.
Make note of the pH. Also, keep in mind that the electrode should remain
immersed throughout the entire titration.
6. Using _FRESH_ sodium hydroxide (NaOH), slowly add this alkaline solution
to the sample, while all of the time swirling. (Note: Having an extra hand
to keep the probe steady & immersed is a great help here).
7. Note the raise in pH & the exact amount of NaOH which you add.
8. As the pH of the combination sample/NaOH solution approaches 7.00, the pH
will begin to climb quite quickly. From this point on, add the NaOH in very
small volumes.
9. When the pH of the combination sample/NaOH solution reaches a pH of 8.20,
you have reached the "end-point" & the titration is complete. Note the
exact total amount of NaOH you have added to the sample & _immediately_
clean the pH meter's electrode with either a commercial probe cleaning
solution or a contact lens cleaning solution.
10. Calculate the TA of the sample using the following formula:
TA = (ml NaOH X Conc. NaOH X 0.75) / ml sample
TA = Total titratable acidity in g/L [grams per liter] as tartaric acid.
(Note: 7.5 g/L = 0.75% = 7.5ppt).
ml NaOH = the volume, in ml, of NaOH which was required to bring the pH of
the combination sample/NaOH solution to 8.20.
Concentration of NaOH = the strength of your NaOH solution. Most commercial
solutions are either "0.1 normal" (which equals 10%) or "0.2" or "1/5
normal" (which equals 20%).
ml sample - the initial sample size in ml. The larger the initial sample
size, the easier & the more accurate the titration. However, having a large
sample also means that you will need to use a larger volume of NaOH to reach
your end-point.
11. Example:
Zinfandel wine is being made from grapes from California's Central Valley.
The grapes are crushed & the must is stirred well. Using a funnel with a
straining screen in the neck, some juice is drawn off of the must & is
placed in a testing jar.
While the juice is in the jar, a thermometer & a narrow range (16-24 Brix)
hydrometer are used to determine the sample's temperature & density.
Next, 30ml of the sample are placed in a small wine glass. A pH meter is
immersed in the sample and the pH is measured at 3.70.
Next, with the pH meter's electrode remaining immersed in the sample
throughout, small amounts of 0.10 normal (10%) NaOH solution are added until
the pH meter reads 8.20.
When the pH meter reaches 8.20, the winemaker notes that he/she has added
exactly 21.0ml of the 10% NaOH.
Now, the winemaker is ready to calculate the TA of the sample:
TA (g/L) = (ml NaOH X Conc NaOH X 0.75) / ml sample.
TA (g/L) = (21 X 10 X 0.75) / 30
TA (g/L) = 157.5 / 30
TA (g/L) = 5.25 g/L.
Finally, since the winemaker wants an initial TA of ~7.0 g/L & an initial pH
of no higher than 3.40, he/she measures out 1.75 grams of tartaric acid per
liter of must (5.25 g/L + 1.75 g/L = 7.00 g/L). The tartaric acid is
dissolved in a small quantity of hot water, and is thoroughly mixed into the
must.
After the acid addition, the must is again tested for TA & pH. This time
the must tests out to a pH of 3.40 & a TA of 7.0 g/L.
Satisfied with the new chemistry, and _more importantly_ with the _taste_ of
the adjusted must, the winemaker commences fermentation.
Miscellaneous Thoughts:
12. If you are comfortable with neither the titration process, nor
evaluation of the must with taste, adjust the must for pH only. Ignore the
TA. When doing this, one would simple start all white fermentations with a
pH of 3.25 - 3.35, & would start all red fermentations with a pH of 3.30 -
3.40. pH alone is an excellent guide for measuring acidity. Consider the
following pH benchmarks:
-Before fermentation: 3.20 - 3.40
-After all fermentations (sugar & ML): 3.45 - 3.55
-Before cold stabilization: 3.55 or less.
-After cold stabilization & at bottling: 3.35 - 3.50
13. It is better to have an initially high TA (say 8 - 10 g/L), than to have
an initially high pH (say 3.55+). Acid can always be removed through MLF &
cold stabilization. A high pH can plague the wine forever.
14. Several things can give the winemaker odd TA readings. These include:
-CO2 in the sample (false high readings)
-Old, oxidized, & weak NaOH solution (false high readings)
-Non-homogenous initial samples (false high or low readings)
-Poorly conditioned, cleaned, or calibrated pH meter (false high or low
readings)
-Extreme sample temperatures [if meter is not self-adjusting for
temperature] (false high or low readings)
-Testing during or immediately after an active fermentation. The evolution
of a wine's acid concentration during fermentation is very complex.
Acids on the magnitude of 2 - 2.5 g/L are created during the fermentation.
Additionally, tartaric acid, on the magnitude of 2 - 2.5 g/L, is lost
throughout & after fermentation. Since the timing of these acid additions &
depletions can not be predicted, acid titration during or immediately after
fermentation has a margin of error of about +/- 4 to 5 g/L!!
15. Finally: don't sweat the TA too much. As TomS has said, evaluate
acidity using your taste, backed-up by the pH. Wise advice.
Hope this helps.
Prosit:
Ed
--
The Viticulture FAQ & Glossary - http://www.itsmysite.com/vitfaq
"I like on the table, when we're speaking,
The light of a bottle of intelligent wine."
-Pablo Neruda
Greg U
1. Following fermentation and MLF, if an adjustment to pH or TA is desired,
is it still acceptable at that point to add tartaric acid?
1a. If the must _should_ have been adjusted before fermentation but wasn't,
should one wait until all signs of fermentation are complete before
adjusting?
2. Housekeeping: Can someone please point me to Joe Sallo's pH FAQ?
3. You indicated that the TA can swing as widely as +/- 4 g/L during active
fermentation. Does this mean that it is not even worth while to take pH
measurements on a daily basis during primary?
-Greg
Zinful
"SchlossGoist" <zen...@hotmail.com> wrote:
> Hi All:
>
> Recently we have had a series of threads dealing with the measurement
&
> adjustment of Total Titratable Acidity (TA) of a wine must prior to
> fermentation.
>
> The following are a series of comments & observations regarding the TA
> testing procedure in general, as well as some miscellaneous thoughts
> regarding the manipulation of acid levels in an unfermented must:
>
you are a saint. I know there are many who arrive for the first time
at this NG at different intervals, so a lot of the questions get asked
over and over. The Pros here, handle each and every one with an air of
professionalism and take the time deal with each inquiry on a personal
basis. I applaud all of you for making this the best NG I'm usre many
have come across in some time. You Ed, have taken the time a few times
to spell things out, or show us how to paint by numbers, one number at
a time. I'm sure you enjoy doing this, but still it takes time and
patience, as well as, a desire to see others succeed and enjoy the art
of making wine.
I personally would like to thank you for your generosity and time, as
well as the many others here who do the same. I believe this NG to be
a goldmine for anyone who wants to learn the finer points of making
wine. I plan to dig in this mine for many years to come.
cheers,
Zinful
--
Fine wine & a good woman,
who needs anything more?
Sent via Deja.com http://www.deja.com/
Before you buy.
SchlossGoist
> Thanks for the informative post.
>
> 1. Following fermentation and MLF, if an adjustment to pH or TA is
desired,
> is it still acceptable at that point to add tartaric acid?
------------------------
Hi Greg:
Yes. Post fermentation acid additions can be done with either tartaric acid
or citric acid.
Adjustments done with tartaric acid will have a more profound impact on
reducing the pH of the wine. However, the wine will need to be cold
stabilized after the tartaric acid addition & the net increase in TA will be
slightly less than what was added due to the precipitation.
Citric acid can be added without the need to cold stabilize afterwards.
However, since the addition of citric acid to a grape wine can upset the
wine's natural acid profile, only very minor additions should be considered.
FWIW, last Vintage I acidified a Lodi Grenache/Carignane/Petit Sirah blend
after the fermentation with 0.5 g/L of tartaric acid followed by cold
stabilization. The net effect of the post fermentation acidulation & cold
stabilization was to increase the TA from 6.0g/L to 6.15g/L and to reduce
the pH from 3.65 to 3.57.
Also, importantly, IMO, the wine does not taste "monkey-with".
--------------------------------
> 1a. If the must _should_ have been adjusted before fermentation but
wasn't,
> should one wait until all signs of fermentation are complete before
> adjusting?...snip...
---------------------------------
As long as the pH does not go through the roof (3.70+), I would wait. I am
sure that others would not.
One thing that I am sure of however: If pH is high, watch it closely
throughout the MLF and adjust the must with tartaric if/when the ML drives
the pH much above 3.70.
----------------------------------
> 3. You indicated that the TA can swing as widely as +/- 4 g/L during
active
> fermentation. Does this mean that it is not even worth while to take pH
> measurements on a daily basis during primary?
----------------------------------
I do not test pH at all during the fermentation. However, at a point
shortly after the yeast fermentation, enough tartrates have precipitated
from the wine to allow the wine's pH to be fairly well buffered. From that
point on, pH readings can be very helpful if one is working at the extremes,
particularly if the wine is to be sent through a MLF.
Dewey & Lucy Thompson
> normal" (which equals 20%).
Ed. Your post is very very good and useful. My congratulations. I do have
one very small, very trivial addition. There is a reason I'm doing this.
The "0.1 normal" is not really "percent". It has to do with the hydroxide
ions (OH) available in the solution. For a single ionic bond like NaOH, the
"normality" is the same as the "molarity". Now, a "mole" is simply the
"gram atomic weight" of the substance. For NaOH, this is 40 grams. In
other words, there is 40 grams per "mole" for NaOH, and a "1 molar" solution
would have 40 grams of NaOH per liter.
A "0.2 normal" solution would have 8 grams NaOH per liter.
The reason that I am posting this is that if someone wishes to make up their
own NaOH fresh for titrations, all they need to do is obtain reagent grade
NaOH and they can mix their own. Add precisely 8 grams of NaOH to water to
make precisely one liter of solution, and you've got it.
Most reagent grade NaOH (in dry form) is somewhat hydrated, so you do have
to know the water factor.
Dewey
SchlossGoist
news:st56tla...@corp.supernews.com...
> > solutions are either "0.1 normal" (which equals 10%) or "0.2" or "1/5
> > normal" (which equals 20%).
>
--------------------
Hi Dewey:
Very good information! Thanks for the correction/clarification.
I pulled out my old, original lab notes on this subject, & they say to call
the "20" or "10" a "concentration which can be treated as a percentage of
molarity".
It's been a long time since I had Chemistry, but I think that this would
jive exactly with what you are saying, no?
Thanks again for the clarification. Excellent info.
st_p...@my-deja.com
>
> Recently we have had a series of threads dealing with the measurement
&
> adjustment of Total Titratable Acidity (TA) of a wine must prior to
> fermentation.
>
> acidity using your taste, backed-up by the pH. Wise advice.
>
> Hope this helps.
>
> Prosit:
> Ed
> --
> The Viticulture FAQ & Glossary - http://www.itsmysite.com/vitfaq
>
> "I like on the table, when we're speaking,
> The light of a bottle of intelligent wine."
> -Pablo Neruda
>
Exactement ce qu'il me fallait et je t'en remercie......St Pierre
Tom S
> Dewey & Lucy Thompson <dltho...@socket.net> wrote in message
> news:st56tla...@corp.supernews.com...
> their
> > own NaOH fresh for titrations, all they need to do is obtain reagent
grade
> > NaOH and they can mix their own. Add precisely 8 grams of NaOH to water
> to
> > make precisely one liter of solution, and you've got it.
> >
> > Most reagent grade NaOH (in dry form) is somewhat hydrated, so you do
have
> > to know the water factor.
That'll get you pretty close - probably close enough for a crude wine
analysis. I say crude, because NaOH in solid form is nearly impossible to
weigh accurately, not only because it deliquesces (sucks water straight out
of the air) but also because it reacts directly with CO2 in the air to form
Na2CO3, both of which will affect the titer of your "standard".
To do it right, you have to first make up a saturated solution of NaOH.
Na2CO3 is not soluble in concentrated NaOH, and will precipitate out. Then
you decant a portion of the clear NaOH solution (*very* corrosive to skin
and eyes!) and dilute it appropriately with water. This must be
standardized against carefully dried and weighed aliquots of potassium
hydrogen phthalate (KHT) to determine the titer of the dilute NaOH.
IOW, It's much easier to just go buy a bottle of 0.1 N NaOH standard
reagent. :-)
Tom S
SchlossGoist
Thank you very much for your kind words.
We are all in this together.
Also, I feel that I get much more from this ng than I give. Just trying to
repay where possible.
For example, Clyde...Would you like me to explain how one can coordinate the
entire winegrowing process around the Sidereal Lunar Calendar?...:-)
Thanks again.
Dewey & Lucy Thompson
call
> the "20" or "10" a "concentration which can be treated as a percentage of
> molarity".
Yes, with the reservation of "simple" bonds such as NaOH. For NaOH, the
normality and molarity is the same.
Dewey
Dewey & Lucy Thompson
> analysis. I say crude, because NaOH in solid form is nearly impossible to
> weigh accurately, not only because it deliquesces (sucks water straight
out
> of the air) but also because it reacts directly with CO2 in the air to
form
> Na2CO3, both of which will affect the titer of your "standard".
"measure with a micrometer, transfer with caliper, mark with chalk, cut with
axe". "crude" is a relative term. It's pretty high tech to what my
grandfather did.
> IOW, It's much easier to just go buy a bottle of 0.1 N NaOH standard
> reagent. :-)
It's easier, but generally more expensive. I purchased 200 ml of reagent at
the local wine shop for two bucks. That will do 20 some tests. For many
people, that's plenty for one season, about 10cents a test.
Fisher sells 100 gram bottles of NaOH for about 10 bucks. That will make
12.5 liters of reagent. That will do what, 12,500 tests? More than I need
for a lifetime, but at about 0.1 cents a test.......
Dewey
Guy
"SchlossGoist" a écrit ...SNIP
>
> Also, I feel that I get much more from this ng than I give. Just trying
to
You are certainly as humble as knowledgeable and cooperative.
Thanks Ed
Tom S
> "measure with a micrometer, transfer with caliper, mark with chalk, cut
with
> axe". "crude" is a relative term. It's pretty high tech to what my
> grandfather did.
Your grandfather probably went by taste, mostly. For an experienced
winemaker, that may be all that is required.
Fancy laboratory apparatus can be put to good use in helping the winemaker
calibrate his/her palate. After all, the goal is to produce a pleasant
stimulation of the senses of taste and smell, so it seems natural to get
them involved in the early stages of the process.
Tom S