Composite sampling has been the industry standard for many years. It works well on the premise that all barrels in a lot contain about the same concentration of free SO2. However, this assumption of homogeneity is far from reality, revealed by data from our research and real-time measurements from the cellars. 

It’s time to rethink whether composite sampling is good enough to control wine quality in our industry, where nature brings more unknowns and surprises to the process. 

Outliers can heavily skew the Composite Sampling results, misdirecting SO2 decisions (and this happens frequently)

Outliers can cause misdirection for winemakers when being included in a composite sample. When outliers on the high side are included, the composite reads high and suggests a lower addition amount, which leaves barrels with lower free SO2 levels at risk. Vice versa, when outliers on the low side are included, the composite reads low and suggest a higher addition amount, running the risk of overdosing the entire lot.

Let’s take a look at an example below showing a 56-barrel group of Merlot, six months into the ageing cycle.

For the example barrel group shown, composite samples taken in three different scenarios lead to concentrations of 20 ppm, 32 ppm, and 36 ppm. If a winemaker receives information from the lab showing the barrel group is at 36 ppm, they may take a different course of action than if they are informed it is at 20 ppm – perhaps no sulfites would be added in the former case, but a significant sulfite addition would be requested in the latter case. This means the very same barrel group could end up having almost twice the sulfite levels depending on which of the barrels happen to be selected for sampling.

But does variance like this happen often? The data suggest that broad variance in free SO2 concentrations is common, if not ubiquitous.

In one study showed in figure below, we examined more than 2,000 barrels from 60 different barrel groups, in 16 different wineries ranged in size from 100-barrel to 6,000-barrel programs and located in several different wine regions across Canada and the United States. You can see the distribution of above-example group (in red) is not abnormal.

As far as outlier frequency, our updated real-time database with 40,000 data points shows one in five barrels of Chardonnay and one in eleven barrels of other varieties are defined as being an outlier for free SO2. That’s pretty frequent.

Higher sampling percentage reduces skewing in Composite results, but also reduces the chance to catch Outliers

You may ask, can we just increase the percentage sampled to make the result closer to lot average? Yes, BUT.

In doing so, we compromise the chance of catching outlier barrels. The skewing power of each outlier entering the composite is now being diluted due to the increased number of barrels sampled.  

And why is this important? For those that make Premium tiers and above, catching and investigating outlier barrels is crucial since each barrel is highly valuable. One outlier barrel running the risk of being downgraded from $68/bottle to $22/bottle can cost you almost $14,000 in revenue loss. Also, if you do rack & return, you will want to isolate any barrels with high risk of microbial/spoilage issues before mixing with the good ones.

Individual barrel sampling is an alternative, and it doesn’t always mean testing every barrel

Tracking free SO2 at the individual barrel level eliminate result-skewing problem and make outliers be seen, enabling winemakers to adjust these barrels specifically. 

This concept only indicates that all tests and records are tied to a specific barrel, and doesn't mean you have to test every single barrel in your facility. It is up to you to decide the sampling tactics such as sampling rate and frequency.

In most cases, it is time-consuming to implement this concept, but the introduction of BarrelWise FS1 has made it highly practical and easy to adopt this method for your winery.