SC-100A manual
2
Version 3.1c
Why Test for SO
2
?
Testing for sulfite (SO
2
) is crucially important for making sure your wine does not spoil by
oxidation or from microbial growth. By monitoring your SO
2
levels, you can make adjustments when
needed, especially before starting primary fermentation, after malolactic fermentation has completed,
after racking or when ready to bottle. To correctly adjust sulfite, you need values for your current free
SO
2
level and your wine's pH. The SC-100A analyzer will help measure your current free SO
2
. You
will need to obtain a value for your pH.
The key parameter in protecting your wine is molecular SO
2
which for most wines should be at
0.5 to 0.8 ppm (mg/L) following secondary fermentation. This in turn depends on the free SO
2
(it can
also be referred to as "unbound" SO
2
) and the pH. Overall, you can reach your target molecular SO
2
by
measuring and adjusting your free SO
2
levels and considering your wine's particular pH. See Table 1.
Table
1
. Free
SO
2
concentrations necessary to attain 0.8 mg/L molecular
SO
2
at a designated pH.
Free
SO
2
(ppm)
13
16
21
26
32
40
50
63
79
99
125
pH
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
We recommend using a sulfite calculator for determining how much sulfite to add to your wines
after taking a sulfite measurement with the SC-100A SO
2
Analyzer. Winemaker Magazine's Sulfite
Calculator at
https://winemakermag.com/1301-sulfite-calculator
can walk you through the process. See
Appendix B for more information on how to adjust your wine for sulfite.
Theory of operation:
Sulfite (SO
2
): The SC-100A, with the SO
2
electrode and reagents provided, can be used to determine
sulfite (or SO
2
)
levels in wine, musts, and other samples. It relies on the Ripper titration based on the
quantitative reaction of the SO
2
with iodine (generated during the titration) which oxidizes the SO
2
in
the sample under acid conditions.
SO
2
+ I
2
+ H
2
O
2I
-
+ SO
3
+ 2H
+
reaction of SO
2
and iodine
When all the SO
2
is titrated at the endpoint, excess iodine appears in solution. This is detected as
current with the SO
2
electrode and signaled by audible and visual indicators. The endpoint is much
more sensitive than the starch color change commonly employed for Ripper titration, and it is sharp
and clear, even when titrating red wines and musts. From the known concentration of the titrant and its
volume required to reach the endpoint, the free SO
2
is simply calculated.
