The Sulfite Calculator is a simple yet very useful tool to quickly calculate the amount of sulfite needed to adequately protect a wine.

It calculates the amount of sulfite based on the current and desired free SO2 levels for any given volume of wine. And it works with either Metric or US units ... no more conversions required!

As an added bonus, the calculator recommends the optimal free SO2 level required to protect a style of wine - red or white - based on its pH level and desired molecular SO2 level

Introduction
Sulfite has been used since the early days of winemaking as a preservative to protect wines from oxidation and microbial spoilage. For home winemaking, sulfite is commonly sourced from potassium or sodium metabisulfite powder or from sodium metabisulfite tablets, known as Campden tablets. Although potassium metabisulfite Campden tablets are now appearing on the market, they are still not very accessible to home winemakers. Some winemakers prefer adding the potassium form to limit the amount of sodium intake in their diets.

Free SO2 is what protects wine and it is created when sulfite is added to the wine. The amount of free SO2 in a wine determines how well it is protected. A minimum level of free SO2 is recommended at each stage of winemaking to ensure problem-free results. Home winemakers must therefore manage and control free SO2 and make adjustments as required.

Free SO2 is measured in milligrams per liters, or mg/L, which is approximately equivalent 1 ppm. Both units are used interchangeably in the industry.

An important consideration in sulfite management is that the effectiveness of free SO2 decreases as pH increases. Therefore, winemakers are advised to compensate for pH when managing the level of free SO2.

Methods For Adding Sulfite
Sulfite can be added using one of three simple methods:

The first method, using sulfite powder, involves dissolving the powder in a little water before adding to wine. It is most useful when large amounts of sulfite need to be added because weighing small quantities is difficult. It is however the most versatile method.

The second method, using Campden tablets, involves crushing the tablets into a powder and then dissolving it in water. Crushing is an obvious disadvantage; however, since these come in 0.44-g tablets, no weighing is required. Their advantage is in the use of recipes with standard wine volumes. It gets trickier when only portion of a tablet is require, making measurements very imprecise.

The third method, using a 10% dilute solution, is very practical, particularly for sulfiting many small batches. A 10% solution is prepared by dissolving 10 g (0.35 oz) of sulfite powder in 50 mL (1.75 fl oz) of warm water and then adding cool water up to the 100 mL (3.5 fl oz) level. For large batches of wine, multiply these numbers by 10 (e.g., 100 g in 1 liter) to prepare sufficient solution.

Using The Sulfite Calculator
To use the Sulfite Calculator, first select your preferred method of sulfite addition. Then enter the current and desired free SO2 levels as well as the volume of wine to be sulfited. It's that simple! The calculator then provides the amount of sulfite to be added using the method you selected. Results are also presented in Metric or US units, as desired.

You may also want to specify the type of wine - red or white - and its pH as well as the desired level of molecular SO2 to get a recommendation on optimal free SO2 level. To determine the amount of sulfite required for the recommended free SO2 level at a given pH and molecular SO2, enter the recommended value as the new desired free SO2 value.

Note: When using Campden tablets, it is difficult to get the exact amount of sulfite when required to split a tablet. The calculator provides results to the closest quarter portion and then provides the actual resulting amount of free SO2. This amount will therefore be different from the entered desired free SO2 level depending on how close the rounding.

Assumptions
The calculator assumes that 57% of the sulfite actually becomes free SO2 to protect wine. Most sulfite sources for home winemakers are mainly available in this form. Other forms may also be available but provide approximately 50% of free SO2. The results are therefore acceptable.

The calculator also assumes that Campden tablets have a weight of 0.44 g, again, the most common form to home winemakers.

WHAT'S NEW IN VERSION 2.0?
Version 2.0 of the SULFITE CALCULATOR now allows winemakers to enter the desired level of molecular SO2 in determining the amount of free SO2 required to protect a wine. The de facto standard for SO2 additions is 0.8 mg/L of molecular SO2 - the calculator uses this value as the default in computations. Molecular SO2 is most inhibitory at levels between 0.5 and 0.8 mg/L. In general, sulfur can become detectable as molecular SO2 approaches 2.0 mg/L.

This method of calculating the amount of additional sulfite required to achieve a desired free SO2 level yields lower quantities than the previous method used in Version 1.0, which was based strictly on the ph of wine. The change was made as winemakers are now trying to reduce the amount of sulfite added to wine.

Downloading Calculator
The calculator was created using an Excel spreadsheet.

To download the calculator now, click here.

For more information on using sulfite and on managing and controlling free SO2, please refer to "Solving the Sulfite Puzzle" in the Winter 2000 issue of WineMaker.

© Daniel Pambianchi, 2008