Des défauts dans 75% des vins de Bordeaux sans sulfites ajoutés
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5% of Bordeaux red wines vinified without sulfites have defects. This is the observation of Edouard Pelonnier-Magimel, post-doctoral researcher at the Institute of Vine and Wine Sciences in Bordeaux.
The doctoral student presented his work at the Oenofutur conference organized on April 22 by the University of Montpellier. “ We bought 52 wines from the 2015 and 2016 vintages labeled without sulfur in supermarkets, wine merchants, or directly from the property, he explains. In parallel, we collected equivalent wines in terms of price, geographical region, and woody impact, but containing SO2 ».
The researchers first measured the total SO2 in all the wines. “Only 43 out of 52 wines supposed to have no added sulphites complied with the regulatory limit of 10 mg/L. 4 contained more than 30mg/L and were excluded from the study” says Edouard Pelonnier-Magimel. The remaining wines were tasted blind by eight students preparing for the DNO (national oenologist diploma) who know Bordeaux wines very well.
“75% of the wines with no added SO2 were judged to be faulty by at least three of the tasters, with a majority of oxidized wines, 25% with notes linked to brettanomyces, and 14% with mouse tastes”. Conversely, only 25% of the 2015 wines with sulphites had defects. “Tasters found none for the 2016 vintage”.
23 tasters then blindly sorted the flawless wines. In olfactory or in the mouth, they succeeded in separating the wines produced with or without SO2. They are also discriminated by geographical origin (right or left bank).
SO2 changes the profile of wine
To evaluate the sensory space of wines without added sulphites, the French Institute of Vine and Wine then vinified the same Merlot according to three methods: without sulphites, without sulphites but with bioprotection, and with sulphites.
“We did this on a batch harvested on the date chosen by the winemaker, and on a second batch designated a week later” specifies the post-doctoral student. In triangular tests, sulfite-free wines were always perceived differently, regardless of their level of maturity. “They were described as fresher with more intense aromas of mint, cassis and baked cherries. Conversely, wines with SO2 were considered more smoky” explains Pélonnier-Magimel.
The researchers then carried out chemical assays and found more methyl salicylate in wines vinified without sulfites, with camphor aroma, and generally found in harvests in a degraded sanitary state. They just have to figure out why.