Improving phenolic extraction with ultrasound treatment

by | Apr 19, 2019 | Winetech Scan

The aim of the study was evaluate the efficacy of a small-scale power ultrasound system to reduce the maceration time needed for the extraction of phenolic and volatile compounds in two grape varieties. A shorter maceration time during harvest will promote a faster turn-around time in fermentation tanks and thus improve the winemaking process.

PROJECT LAYOUT:

  • 400 kg Tempranillo and Monastrell grapes were harvested from Mucia province in Spain and crushed and destemmed.
  • 10 kg stainless-steel tanks were filled with crushed grapes with and without ultrasound treatment (sonication).
  • A pilot scale power ultrasound system with the capacity to treat 400 kg crushed grapes per hour was used for the study.
  • The musts underwent an acid adjustment and were fermented with Viniferm CT007.
  • Three different maceration times were employed for the ultrasound treated grapes: two, three and seven days.
  • The control maceration without sonication was seven days.
  • All treatments were done in triplicate and the cap was punched down twice a day.
  • After alcohol fermentation (AF) the wines were cold stabilised and bottled.
  • Tempranillo wines were analysed after AF and after two and five months.
  • Monastrell wines were analysed after AF and at 12 months.

MAIN TEMPRANILLO RESULTS:

  • The two day maceration wines from sonicated grapes had less colour than the control, but the three and seven day maceration wines from sonicated grapes had the same colour intensity as the control wines.
  • The total polyphenols and total tannins of the three day maceration wines from sonicated grapes were similar to the control wines that had a seven day maceration.
  • The percentage galloylation is lower in wines that had a shorter maceration time compared to the seven day macerated wines, which could lead to less bitterness on taste.
  • There was a higher percentage of suspended cell wall material in sonicated grape musts that could possibly absorb tannins.
  • The ultrasound treatment did not cause large differences in wine aromatic profiles compared to the non-treated control. However, monoterpenes and norisoprenoids were enhanced, which could increase floral notes.

MAIN MONASTRELL RESULTS:

  • Wine made from sonicated grapes with three day maceration did not differ in colour intensity compared to the control wine that was macerated for seven days.
  • After two days maceration of sonicated grapes the total phenolic and tannin concentrations of the control wines were reached (this different to the Tempranillo result).
  • Ester concentrations were higher in wines made from sonicated grapes.

SIGNIFICANCE OF THE STUDY:

This study follows on various other studies that evaluated the effect of ultrasound treatments of grape musts. Ultrasound treatment holds the advantage that it is a non-thermal treatment that can potentially speed up and increase the extraction of valuable compounds in wine.  In this particular study there was varietal effect in that the treatment was more effective on the Monastrell grapes than the Tempranillo grapes, but nonetheless in both cultivars maceration on skins time can be shortened to only three days instead of seven if ultrasound treatment is used.

REFERENCE:

High power ultrasounds: A powerful, non-thermal and green technique for improving the phenolic extraction from grapes to must during red wine vinification



Image: Pixabay

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