Catching problematic barrels

At one of our partner wineries, two premium barrel lots – one Pinot Noir and one Chardonnay – were going through ageing and were intended to sell at a $65-$75/bottle price point. To increase the control over these lots, the winemaker decided to have every barrel measured for Free SO₂ using the BarrelWise FS1 System.

The Free SO2 measurements revealed one barrel in each lot that was significantly outside of the lot average. These two outlier barrels, OB1 and OB2, were flagged and sampled for further lab and sensory analysis. 

Outlier in Lot 1: Error during the SO2 addition process

The first outlier (OB1) was detected with an FSO2 level of 10 ppm, which was significantly lower than the average of 25 ppm for the group. The winemaker investigated the cause and found that the cellar workers had likely missed this barrel when dosing SO2 post-malolactic fermentation. This is not uncommon in cellars of all sizes, as suggested by extensive data collected across many different wineries.

Upon further investigation, this barrel's VA (volatile acidity) was determined to be slightly elevated compared with our reference barrel, Ref 1 (a random barrel within the normal Free SO2 range of the group). However, the sensory analysis showed no discernable difference from the other barrels. By measuring the Free SO2 of every barrel in the lot, the winery was able to catch this outlier before any quality loss occurred, potentially preventing an expensive barrel downgrade. 

Outlier in Lot 2: Microbial issue

Lot 2 had an outlier at 19 ppm, while the average Free SO2 for the lot was 34 ppm. Again, the VA was slightly elevated compared to the reference barrel (Ref 2). However, the winemaker noticed a considerable reduction in fruit character and a distinct ethyl acetate fault during sensory analysis. 

The root cause was suspected to be a microbial issue, which was traced back to the barrel itself. This explanation is substantiated by the fact that the barrel in question had consumed a significant quantity of Free SO₂. This is indicated by the high Total SO2 reading of 73 ppm, as compared to the current low Free SO2 reading of 19 ppm. The winemaker took the necessary action by removing the wine from the barrel and treating it. They also promptly disposed of the barrel to prevent any future issues. 

Although the outlier was detected too late to avoid quality degradation, the knowledge prevented the winemaker from spreading the microbial problem by using the barrel for topping or including it in a homogenization event such as racking or blending. Overall, the winemaker's actions prevented further damage to the wine and ensured the quality was maintained to the best possible extent.

A common issue that gets overlooked

Winemakers often overlook the wide variation of individual barrels that occurs often during the aging process, leading to significant differences in the quality of wine produced. This can result in an expensive downgrade of the wine’s price, often costing tens of thousands of dollars per barrel in lost opportunity for revenue!

Closing Notes on the Value of Early Detection and Barrel-by-Barrel Monitoring

These two barrels required remedial action by the winemaker to mitigate risk and ensure quality was maintained. Although caused by two different issues, both were flagged as requiring further analysis from barrel-by-barrel Free SO2 data alone. Because of the coupled relationship between Free SO2, oxygen, and microbial activity, measuring Free SO2 at the barrel level can provide valuable information and direct the efforts of the lab and winemaker to solve problems in the cellar and maximize quality.

Due to recent advancements in technology, winemakers can now efficiently collect Free SO₂ information on each barrel, an excellent screening tool to flag process errors, over-oxidation, and microbial activity that could affect the quality of the wine. The traditional method of composite sampling, where wine is taken from multiple barrels and combined for analysis, can leave winemakers with major gaps in knowledge of individual barrels, risking oversight of outliers that may degrade in quality and lower the value of the wine.