Impact of oenological tannins on microvinifications affected by downy mildew

Abstract

AIM: Vine diseases are still responsible for economic losses. Previous study in our laboratory, have shown effects of oenological tannins against Botrytis cinerea1,2. According to this, the aim was to evaluate the wine protection by oenological tannins against an another disease, the downy mildew.

METHODS: During the 2020 vintage, infected grapes by downy mildew (Vitis vinifera cv. Merlot) were collected from the dispositive ResIntBio. The 100 kg were crushed, destemmed and dispatch into 10 aluminium tanks. SO2 was added at 3 g/hL. Oenological tannins (grape, quebracho, ellagitannin or gallotannin) were added at 100 g/hL into eight different tanks (4×2 tanks). The two last tanks were considered as control without addition of oenological tannins. Alcoholic fermentation was achieved with Actiflore 33® at 20 g/hL. Malolactic fermentation was achieved with Lactoenos B7at 1 g/hL. Finished wines were sulfited to obtain 45 mg/L of total SO2.

RESULTS: Oenological parameters, polyphenols3 and antioxidant capacity3 were determined and quantified at different stage of vinification (must, end of AF, end of MLF) and aging in bottle (1 and 3 months). Tasting were performed on the 3-months bottles.Regarding tanins analysis (TPI, methyl-cellulose, bate-smith and phloroglucinolisis) no significant differences were observed between the different wines independently of vinification stage. In the same way, for anthocyanins no significant differences were noted. In fact, polyphenol wine matrix was not modified by addition of oenological tannins. However, the interesting results were noted for antioxidant capacity and tasting. Indeed, on the 3-months bottles, significant differences were observed. All the wines added by oenological tannins, except for quebracho, presented higher antioxidant capacity than the control.In addition, wines added by grape, quebracho and gallotanin, were preferred to the control wine even if the difference were not significant. Moreover, the wine added by ellagitanin was significantly preferred to the control wine. According to the profile test, a ranking test was made for each descriptors evaluated. The wine added by ellagitanin, was perceived as really less oxidized, acid, astringent and bitter than the control wine. In addition, the quality of the tannins was highly noted compared to the control wine.

CONCLUSIONS

In conclusion, the tannin and anthocyanins content were not impacted by the addition of oenological tannins. Nevertheless, the wine added by ellagitannin was significantly preferred to the control and presented a higher antioxidant capacity, indicating the ability to this tannin to protect the wine against downy mildew.