Sandy Paetz just sent me an update about what he is doing at the MSU
Viticulture & Enology Program.
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.
TECHNIQUES FOR DETERMINING SULFUR DIOXIDE IN
WINE:
THE ASPIRATION METHOD, THE RIPPER METHOD AND THE TITRETTOR METHOD. -
W.C. PAETZ OCTOBER 2, 2003
Abstract:
We employed three different methods to measure the sulfite content
of different samples of wine.
The “Aspiration” method involved removing SO2 from the wine
by aeration into a solution that oxidized into sulfuric acid. This acid
was titrated and the SO2 calculated from the titre volume.
The “Ripper” method involved titrating the wine sample directly
with an iodine solution.
The “Titrettor” method involved the use of a prepared reagent
sealed in a vacuum ampoule. The result of this test gave the free SO2
in mg/L.
INTRODUCTION:
Sulfur is a preservative, an antioxidant as well as an antiseptic.
These characteristics have distinguished this chemical as the silver
bullet of wine makers for literally centuries. “Sulfur dioxide
(so2) is typically added to the whole fruit or must at crushing. It
is a chemical that has been added in various forms to wines since the
ancient wine makers of Egypt and Rome learned of it’s ability
to prevent wine spoilage.” (1.)
As enologists we will be called upon to discern the exact amount of
various chemicals that can help protect our labor of love.
“Knowledge of the actual concentration of free sulfur dioxide
and the ability to adjust concentrations to a desired level are of immense
importance in fine wine production.” (2.)
The controlling governments’ sanction limited use of this substance
in the final product. In the United States the maximum allowable content
is 350 parts per million. (350 mg/L)
“Sulfur dioxide permits the storage of many types of wine today
that would not exist without it’s protection. In particular, it
permits extended barrel maturation and bottle ageing… The adjustment
must be made within plus or minus 10 mg/ L.” (3.)
The emphasis on controlling sulfites would be incomplete if I did not
mention the U.S. Government requirement. “Since January 9, 1987
wines containing more than 10 parts per million of sulfur dioxide must
carry a label statement such as: “Contains Sulfites” (3.)
One can readily discern the value of being able to measure the free
and total SO2 in a wine sample at any stage of production. This gives
credibility and rationale to support our experiment.
Materials and Methods
Aspiration Method:
1.) 20 mill wine sample Pinot Grigio
2.) 10 mill phosphoric acid 25% solution
3.) 10 mills hydrogen peroxide
4.) 2-3 media drop color
5.) Aspirator with water vacuum 1 l / minute flow rate
6.) Round bottom flask with two peripheral openings plus open on the
top with a stopper.
7.) Receiving vile
8.) Pipette
9.) Micro burette
Method:
Flow rate checked. Pipettes submerged into wine. Air moving through
the sample pulling free SO2 into the impinger with hydrogen peroxide.
20 mills of wine sample placed into the lower ball beaker. 10 mills
of phosphoric acid added to wine sample. Closed with a seal. Impinger
add 10 mills of hydrogen peroxide into top flask. Add 2-3 drops of color
solution indicator until green. Vacuum checked. Adjust h2o to one liter
/ minute of air pulled through system. Fifteen minutes. Titrate end
point.
Ripper Method:
1.) Pipette 25 ml
2.) Conical flask
3.) Burette with stop cock
4.) Iodine reagent
5.) Safety bulb
6.) 1% starch indicator
7.) sulfuric acid 25% solution
8.) Miller Thurgau wine sample
Pipette the sample 25 ml into a clean conical flask. Add 1-% starch
solution with bulb pipette 1 ml. Add 5-ml sulfuric acid. Stir mix.
Place under burette with stopcock drop iodine gradually until color
stays after mixing for thirty seconds. Read amount of iodine to change
color solution.
Titrettor Method:
1.) valve assembly
2.) ampoule
3.) Sample of wine
4.) Potassium lodate iodide with Phosphoric acid reagent
5.) Wine sample Traminette.
Place flexible end of the valve assembly over the titret ampoule.
Fill beaker with wine. Snap the valve assembly at the score mark. Insert
in sample and squeeze control bar to extract some wine sample. Wait
thirty seconds then continue. Shake titrattor to mix watch for change
from blue to clear sample. When end point is observed hold the ampoule
in a vertical position and read the scale.
Results
Please refer to table in appendix for results.
Discussion
All of these methods are interesting but certainly one of them must
be more accurate. Speed and convenience may not have any relevance here.
This is not a measurement that is subject to estimation.
Conclusion
This knowledge is of particular value to anyone who desires to make
acceptable wine. I really believe that it would have been useful to
use the same wine for all of the methods to see if the results are consistent.
If there were a correlation it would be fascinating to observe.
It is also important to note that the SO2 measurement alone means very
little if there is a big variance in the pH of the wine samples. The
knowledge of these variables together would allow you to make an accurate
decision regarding how much SO2 should be added. We need to know how
much is bound, how much is free and what the total is. The ability to
rapidly and accurately test samples for these data would be of significant
value to any enologist.
Appendix
Wine Sample Aspiration Ripper Titrettor
Muller Thurgau 40 46.08 60
Pinot Grigio 12 8.96 16
Traminette 19.2 25.6 42
Chardonnay 5.6 7.68 17
References:
1.) M.W. Baldy Ph.D., The University Wine Course, A Wine Appreciation
Text and Self-Tutorial. The Wine Appreciation Guild. (1998)
2.) R.P.Vine, Wine Making From Grape to Market Place.Plenum Publishers
(2002)
3.) R.Ribereau-Gayon, Handbook of Enology Volume I, The Microbiology
of Wine and Vinifications. John Wiley & Sons Ltd. (2000)