The aim of this study was to investigate if settling red juice before fermentation on skins can increase the phenolic content of the final wines. The reasoning behind this is because anthocyanins and tannins can form complexes with grape cell wall material, such as polysaccharides and proteins, which can precipitate during vinification. Pulp cell wall material has a high adsorption capacity and by removing such material from the must before extraction of anthocyanins and tannins from the grape skins and pips could theoretically increase final phenolic content in wines.
Experimental layout:
- Monastrell (Mourvedre) grapes were harvested from a commercial vineyard in Jumilla (Spain).
- SO2Â and tartaric acid was added at crushing for the traditional fermentation.
- For the settling experiment only SO2Â was added.
- The experimental grapes were pressed at 2 bar in a 75 L membrane press and a pectinolytic enzyme as added to the free run juice. It was allowed to settle for 24 hours at 10 – 12°C.
- The pomace was kept at 5°C.
- The juice was racked and the lees centrifuged and the recovered juice added back to the free run juice.
- Pomace was added back to the clarified juice and tartaric acid was added.
- A commercial yeast was added and fermentation on skins lasted seven days, two punch downs a day.
- All vinifications were done in 50L stainless-steel tanks.
- Wines were bottled after completion of alcoholic fermentation and analysed after three months.
Main results
In the wine made from settled juice:
- Colour intensity increased with 20%;
- Total phenolic content increased with 25%;
- Anthocyanins increased with 23%;
- Tannins increased with either 35 or 43% depending on the method used to measure it.
Significance of the study:
This was a proof of concept study conducted on one grape variety only. Ideally it should be followed up by a more in depth study, which includes a final wine sensory analyses. This technique should also be compared to other techniques currently utilised by winemakers to increase phenolic content (cold soaking, maceration enzymes, commercial tannins, etc.). This study demonstrates that settling red grape juice first, before fermentation on the skins, could potentially increase the phenolic content of wines.
Reference:
Andrea Osete-Alcaraz, Ana Belén Bautista-OrtÃn, Ana Ortega-Regules, Encarna Gómez-Plaza (2018). Elimination of Suspended Cell Wall Material in Musts Improves the Phenolic Content and Color of Red Wines. Am J Enol Vitic. October 2018 : ajev.2018.18042; published ahead of print October 10, 2018 ; DOI: 10.5344/ajev.2018.18042
