The effect of cap management techniques and extended maceration on Merlot



By Karien O'Kennedy
The aim of the study was to evaluate the effect of nine different cap management and maceration techniques on Merlot’s chemical and sensory profile.

Experimental layout:

Merlot grapes were harvested at 27.4°Brix from the UC Davis Oakville Research station vineyard.
Grapes were crushed and destemmed and transferred into 27 jacketed stainless steel 150 kg fermenters.
Acidity and YAN was adjusted and musts inoculated with 20g/hl EC 1118.
The following treatments were performed in triplicate:
  • Pump-overs during fermentation and pressed at dry (no extended maceration)
  • Pump-overs during fermentation and pressed 1 week post dry, 2 weeks post dry, 4 weeks post dry, 6 weeks post dry and 8 weeks post dry.
  • Submerged cap during fermentation and pressed at dry.
  • Submerged cap during fermentation and pressed at 8 weeks post dry.
  • Punch-downs during fermentation and pressed at dry.
  • Both pump-overs and punch downs were performed three times a day.
  • Must and cap temperatures were continuously monitored and adjusted every 15 minutes to maintain 25 – 28°C.
  • At 14°Brix the musts were inoculated for MLF.
  • During the maceration periods the tanks were pumped over once a day for 5 minutes and temperature maintained at 22°C.
  • Wines were racked, SO2 added, cold stabilised and bottled.
  • Chemical and sensory analysis by a trained panel was performed.

Main results:

  • Tannin concentration increased with 2 weeks maceration, but then stayed constant until 6 weeks. Another increase was observed at 8 weeks.
  • Astringency perception was the highest in the longest macerated wines, but the effect was only really significant after 6 weeks of maceration.
  • The punch down treatment with no maceration had significantly less tannins that the pump over and submerged cap treatments with no maceration. This is in agreement with other studies reporting pump overs yielding higher tannin concentrations.
  • Despite the differences in tannin concentrations the sensory analysis showed no difference in astringency perception between the non-macerated treatments.
  • The non-macerated pump over treatment showed less bitterness than the non-macerated punch down treatment as well as the macerated pump over treatments. 
  • Pepper spice aroma (not rotundone related) decreased with maceration.
  • Red fruit aroma increased with maceration.
  • Volatile esters decreased with maceration.
  • Beta-demascenone decreased with maceration.
  • In general volatile alcohols increased with maceration.

 Significance of the study:

The study indicates that cap management during fermentation and extended maceration (or not) can significantly affect Merlot chemical and sensory profile. Careful consideration should therefore be given to these treatments. It must be kept in mind that extended maceration is a very risky practice in terms of potential microbial spoilage.

Reference:

Scott C. Frost, John W. Blackman, Anna K. Hjelmeland, Susan E. Ebeler, Hildegarde Heymann (2018). Extended Maceration and Cap Management Impacts on the Phenolic, Volatile, and Sensory Profile of Merlot Wine. Am J Enol Vitic. May 2018 : ajev.2018.17062; published ahead of print May 29, 2018 ; DOI: 10.5344/ajev.2018.17062

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