# Calculate Molecular SO2

Free SO2 (mg/L)
Wine pH
Current molecular SO2 (mg/L)
Desired molecular SO2 (mg/L)
Required free SO2 (mg/L)

Details:  This calculator will calculate the level of molecular SO2 in a wine based on its pH and measured free SO2 (the proportion of the measured free SO2 which is in the molecular form is dependant on pH).  The required level of molecular SO2 for antimicrobial protection is often given as 0.8mg/L, although sometimes up to 1.5mg/L (Wine Science - Ronald S. Jackson - 2008).

Red Wines:  In red wines, most of the 'free' SO2 is actually pigment (anthocyanin) bound, and is released by acidification of the sample prior to measurement.  Due to this, it is not currently possible to ascertain the level of molecular SO2 in red wines.  Red wines are however, generally far more microbially stable than whites, and thus are typically maintained at lower levels of 'free' SO2.  In summary, maintaining high molecular SO2 in red wines is difficult and ill advised - do not use this calculator as a guide for red wines.

The following formula is used to calculate the molecular SO2 from the free SO2 and the wine pH:

Molecular SO2 = FSO2 / ( 1 + 10( pH - 1.81 ) )

Where:
FSO2 = Free SO2
pH = pH of the wine sample

The formula is then rearranged to calculate the required level of free SO2 to achieve a desired level of molecular SO2:

Free SO2 = MSO2 * ( 1 + 10( pH - 1.81 ) )

Where:
MSO2 = Molecular SO2
pH = pH of the wine sample

VinoCalc by Jonathan Musther  -  jon@musther.net