SO2 Binding After an Addition

When an SO2 addition is made to a barrel or tank, a portion of the SO2 quickly becomes bound and is no longer available for lasting protection against microbial or oxidative threats. Winemakers must plan their additions to compensate for this rapid binding, but by how much is an often-debated topic.

The most common approach we see is the “SO2 Addition Multiplier.” For example, if your target free SO2 for a particular barrel is 35 ppm, and the barrel is currently reading at 20 ppm (Δ = 15 ppm), an addition multiplier of x = 1 (no extra SO2) would be a 15 ppm add, an addition multiplier of x = 1.5 would be a 22.5 ppm addition.

The Optimal Multipliers, According to Our Real-Time Database

Selecting the correct addition multiplier is the key to reliably hitting free SO2 ppm targets. We see winemakers using addition multipliers ranging between 1.0 and 1.8, and most winemakers have a preferred multiplier that they use for all additions. BarrelWise collects thousands of data points every month, including pre-addition free SO2, SO2 addition amounts, and post-addition free SO2, which allows us to calculate which addition multipliers are most effective from our dataset. 

Our data showed two distinct clusters of optimal addition multipliers: red wines and Chardonnay, the white wine for which we have the most barrel-aging data.

Our recommendation of addition multipliers to use with barrel-aging wines: 1.55 for Red Wines, and 1.3 for Chardonnay.

Some additional factors to consider when setting your own addition multipliers that are likely to affect rapid binding free SO2 include how long the wine has been in the barrel, the oxidation state of wine, and the barrel’s hygiene history. 

As the dataset used to calculate these factors continues to expand and evolve, we will keep updating the addition multiplier values and start to provide more resolution on what works best for different winemaking situations.

Managing Additions with BarrelWise Tools

Winemakers can calculate SO2 addition amount using the SO2 addition calculator on the BarrelWise website, or specify Addition Multipliers for each lot in the BarrelWise Winemaker Portal (for customers).