We just had another update about what Sandy Paetz is doing at the
MSU Viticulture & Winemaking School - “pH and
Acid Titration”
This program was brought to our attention a few years ago when
a MSU student, Bernard Call, who is taking this course, purchased some
grapes at our farm and was carefully measuring the brix of the grapes
with a refractometer. The following year he returned to our farm after
being in the program for one year and he was very enthusiastic, interesting
and knowledgeable about the course.
Sandy Paetz, one of our past Sales Stand Associates, had also
enrolled in the MSU program. When the two of them found out
that they both were taking the courses, the conversations became very
stimulating and they agreed to forward some of their program notes to
us for our newsletter.
We have some inside stories of what Bernard and Sandy are doing
at MSU.
Bernard Call stopped by last week with a bottle of late harvest
vignoles. I missed him (I was out working bees) but he left
a note saying that he was soon going to plant some reisling vines on
40 acres that he just purchased up in the Northern Michigan wine area.
The wine was delicious, by the way. It was a heavy, rich, sweet white
dessert wine. A very nice vignoles.
“pH and Acid Titration”
W.C. PAETZ - January 21, 2004 Michigan State University
Abstract:
During our lab exercise we followed the protocol for discerning accurate
measures for pH and titratable acidity for six different wines. As a
prelude to this analysis the calibration of the equipment and staging
of samples was carried out to facilitate consistent and expedient laboratory
results.
INTRODUCTION:
A comprehensive program for grape and wine analysis includes several
critical metrics. Being able to discern the pH and titratable acidity
are essential skills. These factors come in to play at every stage of
wine production from harvest, as juice or must, after primary fermentation,
during problem solving, prior to and during aging and finishing and
especially prior to bottling.
For the enologist to safely and to effectively produce accurate results,
they must be familiar with the equipment and the tests.
With regard to pH, this factor must be known to control wine quality,
to avoid spoilage and to strategically use chemicals and acids to protect
the final product.
With regard to titratable acidity, “(1.) Fruit, including grapes,
contain different types of acids. Too much acid renders a wine undrinkable.
On the other hand, if wine does not have enough acidity, the result
is flat or insipid tasting wine. That’s why it is important to
check the acid levels and adjust if necessary.”
“(2.) There are two ways to measure an acid. They are by titration
for total titratable acid and by measuring pH. One of the hardest things
to understand is that they do not measure the same thing and do not
correlate with one another. In my mind if they both measure acid, one
should be able to convert one to the other but it just doesn’t
work that way.”
“(2.)Acids are molecules and they must be made up of at least
two atoms. At least one of those atoms must be hydrogen. This hydrogen
ion is the magic part of acid, has a positive charge and is written
[H+].” Titration measures the total [H+] ion concentration, the
ones floating around in solution, plus the ones still holding on to
their constituents. The pH measures only the ones that are dissociated
and floating around in the solution. Titration measures how many could
react. The pH measures how many are ready to react.”
“(3.) Like a lot of other things in life, pH is what you make
of it. It is easy to learn to use pH, and you don’t really need
to understand it. Most of us don’t understand the cars we drive
or the TV sets we so blithely manipulate. Start by recognizing pH as
a very important number that can help you make better wines.”
Total titratable acidity is not a measure of total acid, but of the
acid that is available to react with the NaOH solution with which we
titrate, pH is a measure of the acid strength in the must or wine. It
is the pH, rather than the total acidity, which indicates the ability
of the must to resist oxidation and invasion by bacteria, and which
determines how much SO2 is needed.
These are some of the reasons that support this study.
Materials and Methods
Titratable Acidity:
Equipment:
1.) 250 ml Erlenmeyer flasks
2.) 10 ml Volumetric A Pipet
3.) Titration assembly (burette set up)
4.) 0.1N Sodium Hydroxide
5.) pH meter
6.) Wine Samples
7.) magnetic stirring bar 3/8
8.) distilled water
Method:
1.) Standardize pH meter.
2.) Fill burette with 0.1 N NaOH.
3.) Add distilled water to ensure pH meter covered.
4.) Rinse pH electrode with a few ml of distilled water.
5.) Place in wine sample
6.) Position burette so outlet is above beaker.
7.) Place and activate stir bar.
8.) Tartrate the pH of sample to 8.2
9.) Read measure of NaOH and record this volume.
10.) Multiply by .75 Titre value.
“pH Measurement of Wine Sample”
Equipment:
1.) Corning Scholar 425 pH meter
2.) Beakers with various samples
3.) Distilled water
4.) Wipes to dry electrode probe.
5.) 3/8 magnetic stir bar
Method:
1.) Standardize the pH meter.
2.) Place stir bar.
3.) Immerse the electrode into wine sample beaker.
4.) Slowly activate stir bar in sample beaker
5.) Take reading of stabilized pH from meter and record.
6.) Rinse and wipe electrode and place in storage solution while preparing
next sample for analysis.
Results
(Figure 1)
Cultivar pH TA
Carbonic Maceration Foch 2.95 9.6
Delaware 3.02 7.6
N.W. Vignoles 3.36 12.4
Sparkling Foch 2.91 12.4
Late Harvest Vignoles 3.12 14.9
Frontenac Juice 3.03 18.5
Discussion
There is a need to exercise caution when using a pH meter as pH is exponential
and quickly moves from pH 7 to pH 8. The use of this equipment when
analyzing red wines is critical as the ability to discern the end point
when using Phenolphthalein or another color indicator is quite problematic.
According to Jackson, (5.) “A pH range of 3.1 – 3.4 is the
goal for white wines and 3.3 to 3.6 for most red wines.”
Conclusion
This study was not only worth while but extremely important. A person
can not consistently make desirable wines with out a profound understanding
of these analytical tests and ensuing results. One needs to be able
to confidently follow the test procedure and know what the results mean
in terms of the status of the wine and what desirable metrics should
be aspired to as well as what action needs to be taken to correct and
protect the wine.
Appendix
Refer to figure 1 in text.
References:
1.) Martin Jordan, Host of Video, 1995 “Making Wine”, The
comprehensive how to video for making wine in your home. Bacchus Productions
Inc.Toronto, Ontario
2.) Acid Titration, G. Goodwine , http://www.geocities.com/medievalbrewers/acid.html
3.) J.E. Underhill, pH Without Pain, The Grapevine a news letter for
winemakers in British Columbia.
http://www.bcawa.ca/winemaking/ph.htm
4.) R.S. Jackson, Wine Science Principles Practice Perception, Cool
Climate Oenology and Viticulture Institute, Ontario Canada. (2000),
Page 240
More MSU articles
MSU Grape Website
- Lots of very good information for the grape grower.
Weather, vineyard scouting, pest management, cultural practices, links,
study & training.
MSU study & training
programs - The Viticulture Program is a 16 to 24-month
comprehensive program of study focused on the planning, establishment,
and management of a vineyard. The Enology Program is also a 16 to 24-month
program that emphasizes the chemistry and analytical techniques involved
in wine production.