Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
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July/August 2009
Délestage: Step 1
Délestage is a rack-and-return process modified to deport seeds, illustrated here. Fermenting juice was deported from a bottom valve through a dejuicing sleeve with holes 1/10-inch in diameter. Seeds were retained within the sleeve, and the deported juice was pumped to a separate tank while the cap was allowed to drain. Process was conducted once per day until the completion of fermentation or dejuicing, depending on the particular trial.
themust temperature, and added to each lot (24 g dry yeast/100 L).
The six equal-weight lots were randomly assigned to treatments consisting of 1) control, conventional fermentation, with cap manually punched down two times per day, or 2) délestage, consisting of a rack and return procedure with seed removal conducted once per day until dryness, as follows.
Following cap rise, fermenting juice was drained from a bottom valve through an external cylindrical dejuicing sleeve (2.39 mm diameter holes) into a stainless steel vat. Seeds were retained within the sleeve.
The juice was pumped to a separate tankwhile the dejuiced capwas allowed to drain freely for two hours. Juice was then returned to the top of the cap via a tank cap irrigator, using deflection plates to minimize skin breakage. The separated seeds were drained free of liquid, weighed, and discarded.
Treatment and control vessels averaged filled height-to-diameter ratios of 0.64 and 0.75 for the délestage and conventional fermentations, respectively.
Fermentations were conducted at an average liquid temperature of 28°C (range 26° to 35°C) and an average cap temperature of 30°C (range 28° to 37°C) in 1,000-L capacity vessels. Pressing was performed at dryness (2.0 g/L reducing sugar) using a tank press to 1 bar. Freerun and press-run wines were combined.
Délestage: Step 2
Juice was brought back to top of the fermentation tank using a cap irrigation system. Délestage, therefore, involves two main features which are impacting the tannin profile of the wine (and therefore the structural/textural qualities):
1) removal of seeds could reduce the contribution of immature phenols;
2) oxidative polymerization could result in partial reduction of monomeric pigments as they are incorporated into large polymeric pigments.
(For more details see kiosqueuk/procedur/delestage.htm or onlinepublications)
Tannins in the skins and seeds can combine with anthocyanidin glycosides (anthocyanins) to form polymeric pigments.36 These pigments are believed to be formed by condensation products of malvidin-3-glucoside and various procyanidins created through acetyl bridges.9,26 Anthocyanin-tannin complexes can be produced by binding between the C-4 of the flavylium salt and the C-8 of catechin.21,27
D.O. Adams et al. reported extractable seed tannins in Syrah grapes declined by about half from véraison to harvest, and were about three times greater than skin tannin concentrations.2 Grape skin phenols are more easily extracted during fermentation than those of seeds and stems.18
Although skins contain a lower concentration of total and polymeric phenols than seeds,13 they may be the primary source of polymeric phenols in wine.14 For the first five to seven days of fermentation, phenolic compounds are extracted mainly from skins, followed by extraction from seeds.23
Several reports have suggested that seeds contribute significant concentrations of proanthocyanidins to wines,15,29 while others have reported the seed contribution to be limited.4,24,39 These contradictory observations may be the result of differences in cultivar, fruit maturity, and winemaking style.
For example, duration of maceration primarily influences the extraction of phenolic compounds from the seeds,40 while fermentation temperature appears to be a primary factor influencing extraction from skins.23
Délestage, or rack and return, is a maceration technique designed to help optimize the exchange between the liquid and solid phase by emptying the fermentation vessel of liquid while aerating the juice.
Following several hours of cap draining, the liquid is gently pumped over, or returned, to the cap. This procedure is designed to help oxygenate, while minimizing mechanical grinding of the skins, seeds and stems (Dominique Delteil, personal communication, 2003). This study evaluated délestage in conjunction with partial seed removal, to determine the impact on Merlot wine composition for three seasons and on Cabernet Sauvignon for one season.
Materials and Methods
MERLOT fruit (approximately 8,500 kg), grown in central Virginia, was hand-harvested in each of three years at a minimum of 21.0° Brix (a common soluble solids concentration for Merlot grown in central Virginia). Fruit was immediately destemmed, crushed, and divided into six equal-weight (1,416 kg) replicates. Must fermentable nitrogen levels were measured,10 and adjusted to 250 mg/L adding either Fermaid K™ (Scott Laboratories, Petaluma, CA) or Superfood™ (The Wine Lab, Napa, CA). Sulfur dioxide (30 mg/L) was added at crush to each lot.
Each must was given a cold maceration (cold soak) period of 24 hours at 10°C, prior to fermentation. D-254™ yeast (Scott Laboratories, Petaluma, CA) was hydrated, microscopically examined for budding, viability and purity, cooled to within 3°C of