Enology Notes

Enology Notes #78, August 1, 2003

To: Regional Wine Producers

From: Bruce Zoecklein, Head, Enology-Grape Chemistry Group, Virginia Tech

Subject: Short Vatting

1.Short Vatting

Perhaps the greatest challenge to the production of consistent wine quality in Virginia lies in the ability to adjust winemaking protocol to fit seasonal variations. A problem and concern this season has been the extensive rainfall resulting in poor fruit set, low crop, a great deal of vegetative growth, and fungal disease pressures.

The environmental conditions during bloom resulted in uneven set, which may provide a high degree of uneven ripening. If the wet weather continues, the extensive vegetative growth will continue, resulting in a delay in the rate of fruit maturity. This, coupled with asynchronous fruit development, can cause a lack of phenolic maturity, and a high concentration of undesirable aromas.

Winemaking adjustments to suit the season is a requirement for premium wine production. One such adjustment to consider for this season is short vatting. This term is applied to wines made by dejuicing prior to dryness, sometimes considerably prior.

The goal of short vatting is selective extraction. The aims of traditional short vatting include the rapid diffusion of desirable pigments, tannins and polysaccharides from the skins and the pulp, and the stabilization of phenols and aromatic compounds (Delteil, 2000). Questions to ask include how to determine if short vatting is a desirable production method, and at what stage in the fermentation should wines be dejuiced.

Both determinations should be based upon an understanding of the fruit and objectives. The specific objectives include color, structure (the balance of phenolic and acidic elements), and aroma. These objectives have to be established, based on knowledge of fruit ripening parameters and the degree of asynchronous ripening.

Thinning at the time of veraison is a standard method used in Virginia to help minimize the degree of uneven development at the time of harvest. One concern this year may be the already depressed crop load and the problems associated with reducing the crop in the future, and possibly increasing vegetative growth.

At or near the time of harvest, each block should be monitored for the degree of uneven ripening. This can be done by berry sampling. For accuracy of +/- 0.5 Brix, 5 x 100 berry samples are required. Processing each 100 berry lot separately allows for the determination of the coefficient of variation, or the relative difference among samples.

If the variation among samples from a individual block is not large, then the degree of uneven ripening is not large. The greater the degree of uneven ripening, the shorter the vatting period should be.

Processing involves the following considerations. Avoid excessive berry breakage. Enzyme addition helps in extraction. This will also lower the concentration of reductive tones, by allowing greater ability to separate heavy from light lees. Heavy lees are those which precipitate 24 hours immediately post-fermentation. Wines should be removed from heavy lees.

Light lees are those which precipitate more than 24 hours post-fermentation, and those lees should be retained, depending on the varietal, fruit conditions, and wine style (Delteil, 2001) (See Enology Notes # 25, 41, 61 and Vintner’s Corner Vol. 14, No. 3; Vol. 17, No. 5).

Yeast selection is also quite important. Those who were at our Mouthfeel Seminar with Dominique Delteil were able to evaluate a set of red wines, which demonstrated the impact of yeast on mouthfeel components. A high mannoprotein- or polysaccharide-producing yeast would be desirable in the case of uneven ripening.

Delestage, with or without seed deportation, allows for fairly rapid diffusion without over-extraction. Excessive extraction increases the phenol load, resulting in a high concentration of astringency, tannin intensity, dryness and bitterness.

Delestage has the advantage of being gentle, avoiding over-extraction as well as being oxidative. The oxidative nature of this processing technique allows for increased polyphenol polymerization if this is done daily, resulting in increased color stability and mouthfeel softening (See Enology Notes # 23, Vintner’s Corner Vol. 15, No. 3). Relatively cool fermentation temperatures of both the cap and juice have a large impact, by helping to avoid over-extraction.

After dejuicing, short-vatted wines should be racked off the heavy lees 24 hours post-fermentation. Microoxygenation or splash racking may help evolve the tannins, depending upon the variety and the degree of polymerization which has already occurred (See Enology Notes #23, 33, 36).

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Dr. Bruce Zoecklein
Professor and Enology Specialist Head Enology-Grape Chemistry Group
Department of Food Science and Technology, Virginia Tech
Blacksburg VA 24061
Enology-Grape Chemistry Group Web address: http://www.vtwines.info/
Phone: (540) 231-5325
Fax: (540) 231-9293
Email: bzoeckle@vt.edu