Fine wines are usually aged in oak barrels, and every wine maker knows the practical challenges that this process poses, both in terms of labor requirements and safeguarding wine quality. This article will discuss an opportunity to streamline the process and minimize typical bottlenecks by transferring the routine Free SO₂ analysis function away from the winery lab, and into the cellar.

Problems with the current barrel work process

Barrel ageing creates a number of risks for the quality of the wine, which needs to be constantly managed by the winemaking teams. Barrels are moved around the cellar, samples are taken for lab analysis, and the results inform subsequent actions. For a typical mid-large size winery, this routine barrel work process looks something like this:

  1. Winemakers issue a work order specifying which barrels will be worked that day
  2. The cellar crews unstack barrel racks in a centralized location (some wineries work barrels in place, but in our experience, this is more common at the smaller facilities)
  3. Wine samples from a random subset of each barrel group are combined in a composite and taken to the lab
  4. Lab analyses the samples for a range of parameters, including Free SO₂
  5. Winemakers may conduct sensory ‘health checks’ on the composite samples
  6. Winemakers determine whether SO₂ needs to be added to the groups
  7. Cellar crews execute the specified SO₂ additions, and top the barrels
  8. Barrels are re-stacked on racks until the next cycle
Current process flow for routine barrel work

This workflow presents two major challenges.

A. Labor inefficiency: once samples are collected, a lab or cellar worker must physically carry the samples to the lab for analysis (step 3). At large wineries, this can mean a 5–10 minute walk to and from the lab. Depending on the lab’s set up, analysis can be time consuming – aeration oxidation method for Free SO₂ analysis takes ~15 mins per sample. The cellar crew may then have to wait for analysis results to be reviewed by the winemaking team to determine the actions (steps 4-7), which, anecdotally, can take anywhere between a few minutes to over a day, depending on the winemakers’ availability.

Here, information must flow from the cellar to the lab, from the lab to the winemaker and back to the cellar. At least 3 different people are involved, all separated by a physical distance from each other. From the cellar’s perspective, the lab and winemakers are a bottle neck.

B. Opportunities for human errors: If the winery tracks which barrels are sampled (step 3), the crew must label the sample bottles accordingly. This creates an opportunity for errors such as mislabeling, ineligible handwriting, wine stains obscuring the label, etc. The sampling process itself can often lack randomness (bias towards barrels low in the low stacks, or on one side of the rack). When making additions (step 7) it is all to easy to miss a barrel, or dose a barrel twice by mistake, which exacerbates the natural variance in SO₂ levels between barrels

Barrel work is monotonous, and loss of concentration can result in simple mistakes that can have real implications for the quality of the wine. Some form of automated checks and balances to highlight mistakes as they happen would address this.

 N.B. The other key challenge is that composite sampling of a sub-set of a group disguises the differences in wine health between individual barrels, and results in preventable wine quality issues that often lead to declassification / downgrades of the wine. We will not dwell on this subject here, as it has been extensively covered in this article & video.

Efficiency of moving Free SO₂ analysis from the lab into the cellar

Let us see what happens if a winery begins analyzing Free SO₂, the key parameter which determines action (SO₂ additions), right in the cellar:

  1. Winemakers issue a work order, but this time it includes rules for making SO₂ additions based on results for that group
  2. Cellar crews unstack barrels
  3. As before, except the urgency of walking samples to the lab is reduced
  4. Cellar crews measure Free SO₂ themselves in the barrels, right after de-stacking and opening them
  5. Immediately after getting Free SO₂ readings, the crews add SO₂ according to the rules specified in step2. above. They can also top the barrels and re-seal them
  6. Once group as been worked, the barrels are restacked
  7. As before, lab still analyses the samples for a range of parameters, excluding Free SO₂ as part of regular procedure
  8. As before, winemakers may conduct sensory ‘health checks’ on the composite samples
Updated process where sulfite analysis is done at the barrel

Here, steps 1-3 are nearly identical – work order is issued, barrels are located, and composite samples are collected for comprehensive analysis and lab checks. The only difference, is that winemakers pre-set simple SO₂ addition rules for each group, based on results. For e.g.:

  • If measurement is over 30ppm, no addition is necessary
  • If measurement is between 20ppm and 30ppm, crews add 10ppm of SO₂
  • If measurement is between 10ppm and 20ppm, crews add 20ppm of SO₂.
  • Etc.

In Step 4 the crews conduct the Free SO₂ analysis right at the barrel, then add SO₂ based on the measurements and the pre-set rules in the work order and top the barrels. Here, speed of sample collection and analysis become key to maintaining throughput. The lab and winemaking team are no longer bottle necks, as the crews have all the information needed to continue the work.


By transferring the Free SO₂ analysis capabilities from the lab into the cellar, wineries can streamline routine barrel work processes, reducing downtime and saving labor. Enabling the cellar workers to conduct the analysis and consistently act on the results according to predetermined rules can improve consistency and reduce opportunities for human errors, benefiting wine quality.

The high throughput of modern Free SO₂ analyzers like BarrelWise FS1 can also help to identify, and correct wines that are at greatest risk of spoilage. As we discuss at length in our Free SO₂ Management video, at-barrel analysis uncovers the variance in SO₂ levels between individual barrels. It also supports customized SO₂ additions for individual barrels. Crews are guided to add extra SO₂ to barrels that are lower than average, and skip additions to barrels that are higher than average. This not only improves the overall protection of the wine from spoilage, but also optimizes SO₂ use, and lowers the total SO₂ levels of the finished wine.


Find out how the BarrelWise can help you save time and reduce spoilage risk in your barrel program.