The 'best before date' of the dark (titrating) solution is indicated on the bottle label; it is usually 2 to 3 months ahead, although we have found it to be sufficiently accurate after 12 months, if kept sealed and in the dark.

Fill the cylinder with wine or must accurately up to the '0' mark (approx 10 ml). When doing this hold the cylinder at eye level and take care that the lowest part of the meniscus just touches the '0' mark.
From the dropping bottle add Dr. Stührk's dark (titrating) solution, drop by drop. Initially the blue colouration of the dark liquid disappears immediately when the measuring cylinder is shaken briefly. As soon as the colour begins to disappear only slowly, the contents of the cylinder must be thoroughly mixed by applying the thumb to the top of the cylinder and tipping it.
Eventually, when a faint red-violet colour remains for a short time (1 to 2 seconds) the determination is complete.
A more marked and persistent violet colouration means a drop too much has been added, giving too high a reading.
The level of the mixture in the cylinder is accurately read off in the same way as when adjusting the level of wine initially; at the lowest part of the meniscus. The scale gives the content of free SO₂ in milligrams per litre.

Total Sulphur Dioxide (SO₂) in wine and must, by Dr. Stührk's method:-

The supplementary equipment needed comprises a so-called dilution cylinder (with the marks "Getränk - I - II", which in its external dimensions is the same as the titrating cylinder) and two different solutions (solution I and solution II).

The method is suitable for white and rosé wines and particularly for red wines. The time required for the determination is about 10 minutes.

The determination of total sulphur dioxide is carried out as follows:-
1. Rinse out the dilution cylinder with the wine to be analysed.
2. Pour the wine into the cylinder up to the mark "Getränk". Adjust the level accurately so that the lowest part of the meniscus justs touches the '0' mark.
3. Add solution I from the dropping bottle, bringing the level (the lowest part of the meniscus) up to the mark "I" on the dilution cylinder.
4. Allow to stand for 5 to 10 minutes.
5. Add solution II from the dropping bottle, carefully, until the lowest part of the meniscus is just level with the mark "II".  Take care - if too much of the solution II is added then steps 1 to 6 must be repeated.
6. Quickly but carefully mix the contents by rotating the cylinder; keeping it upright.
7. Quickly transfer some of the solution obtained to the titrating cylinder (up to the '0' mark) and titrate in the same manner as in the determination of free SO₂ (above).
The result that is read off the scale (SO₂ mg/ltr) then has to be doubled. For example, reading 120 mg/ltr; the total SO₂ in the wine = 240 mg/ltr.

It is important to point out that the error in the determination is under 10% only if the procedure is carried out with care.
In particular, after adding solution II (step 5 in the instructions) the next two steps must be carried out without delay.
If the solution is allowed to stand for any length of time, loss of SO₂ unavoidably occurs and the values obtained are somewhat lower than the actual values.

The solutions I and II have unlimited life and can be used for about 30 determinations.

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