How to measure molecular SO2 in wine

Without sending samples to laboratories

Imagine how convenient and practical it would be if you could measure the content of molecular and free sulfur dioxide directly above the wine barrel in your cellar without taking a wine sample to the laboratory.
The Sacks Laboratory at Cornell University in Ithaca, NY, recently described a new approach to measuring molecular SO2 , called the ” headspace gas detection tube ” (HS-GDT) that does not disrupt anthocyanin-SO2 complexes.

Simple and cheap method

A simple and inexpensive method for measuring SO2 uses overhead gas detection tubes used in the mining industry to accurately measure molecular SO2 , this time in wines.
Using this method, we found that standard approaches (Ripper titration, irradiation-oxidation of OA and FIA) overestimate the amount of free and bound SO2 , especially in red wines.

An easier, cheaper and
more accurate way of measuring

We have developed an easier, cheaper and more precise way of measuring free and molecular SO2 . Values ​​obtained with this technique may be better predictors of wine stability than standard analytical methods and may simplify SO2 measurement for small wineries.
This new HS-GDT method is also a better indicator of yeast growth in sweet wines than conventional methods.

How to make the apparatus

Disadvantages of classical methods 

In order to obtain oenologically useful information, analytical methods for SO2  must distinguish between the free form with its protective properties and the bound forms that do not have these properties. Common analytical methods for free SO2  in wineries include iodometric titration (Ripper’s method) and the aeration-oxidation (AO) method, and others that are less widely used.
This acidification step, together with the consumption of free SO2 during analysis, can result in the release and subsequent measurement of loosely bound SO2, especially from anthocyanin-bisulfite complexes. As a result, standard measurement approaches will overestimate (determine a higher content) free SO2, especially in red wines.

No reagents required

Here is described the method and apparatus by which free SO2 is measured and calculated without the use of reagents, which results in “real” free SO2 in the analysis results .
From the data for the content of “real” free SO2 we further calculate the current content of molecular SO2 .

In this way, we have control over molecular SO2 during the entire vinification until the wine enters the bottle, without sending samples for analysis.

The only part that is purchased

The main part of the apparatus for measuring free and molecular SO2 in wine are GDT tubes, which we must buy from the supplier with the most favorable prices.
The cost-effectiveness of using this apparatus is not questionable because the prices of GDT tubes on the market are quite acceptable.

It should be borne in mind that one tube can be used more than once, which depends on the amount of free SO2 that was measured in the previous wine sample. The SO2 analysis   can be repeated with the GDT, until the tube is fully used.

The device has only three parts!

Syringe or syringe

BD syringe (Syringe) of 60 or 50 ml with Luer-Lok threaded tip for a reliable connection to the faucet.
It is available in the infusion set at the pharmacy.

Polycarbonate faucet

A one-way polycarbonate faucet with a male Luer-Lok fitting and a short piece of silicone tubing, approximately 3mm ID x 6mm OD. It is in the infusion set.

GDT tube

Using GDT tubes replaces all the reagents you use in the laboratory to measure the SO2 content of your wine. I recommend that you get Japanese-made Gastec pipes
for the construction of your equipment . Set of 10 tubes.

From the e-book you will learn

The importance of SO2
control

Correct measurement of molecular SO2 is crucial for wine quality.
All standard approaches to free SO2 greatly overestimate the amount of free and molecular SO2 in all wines due to the presence of loosely bound compounds such as anthocyanin-SO2 .
We have developed a simple, low-cost method with gas detection tubes (HS-GDT) that accurately measures molecular SO2 in white and red wines.

The principle of operation of the device

The described approach by scientists from the American Institute of Oenology used a syringe (syringe) instead of a special pump to create a balanced closed space above the wine sample , and then expel the space from the wine through a commercial gas detection tube.
GDT-tubes contain a colorimetric SO2  -selective reagent so that the length of the color change on the GDT is proportional to the concentration of the analyzed gas, i.e. SO2 .

Using the device

A measured amount of wine is placed in a syringe and the wine and its upper space are allowed to reach equilibrium. The syringe plunger is then depressed to force a measured amount of space (50-200 mL) into the SO2 gas detection tube , which changes color in direct proportion to the concentration of free SO2 in the space above the sample.
This takes into account the speed of squeezing the free space above the surface of the wine sample into the syringe.

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