Enology Notes

ENOLOGY NOTES # 14 March 2, 2001

To: Virginia Vintners and Prospective Vintner

From: Bruce Zoecklein

Subject: Budget Reduction/Hiring Freeze, Atypical Aging, Winery Planning and Design Workshop

Budget Reduction/Hiring Freeze. Governor Gilmore has order an immediate hiring freeze, travel restrictions, and a 15% budget reduction for Virginia Tech. This could put our research winery renovation and the filling of a vacant position in our lab on hold. I will let you know how this plays out.

Atypical Aging. We are involved in a formal study with colleagues in California (Fresno State University and Cal Poly San Luis Obispo) evaluating grape nutritional (nitrogen) status as determined by several analytical methodologies. This research continues efforts to develop and optimize the Formol titration method (which can be easily used by all wineries and growers) for determining assimilable nitrogen levels. Another area of this research involves determining how grape nitrogen levels relate to vineyard location and management practices. Poor nitrogen nutrition can have a dramatic effect on the sensory characteristics of wine as a result of: stuck or protracted fermentation, excessive acetic acid and aldehyde production, oxidative degradation and a low ratio of esters to fusel oils. (For additional details see Vintner's Corner Vol. 15. No. 2 March/April, 2000, available on my web site.)

Grape nitrogen also appears to be related to a sensory phenomenon know as untypical or atypical aging. This is an aroma/flavor fault first noted in some white German wines produced in 1988. Wines with this taint loose their varietal character very early and take on atypical aroma/favors which have been variously described as a naphthalene, dirty dish rag and wet towel. Since it was first reported, it has been identified in other wine regions of Europe, the Pacific Northwest, California and New York. We have seen a few incidences of this in Virginia as well.

This sensory problem is not well understood but appears to be linked to the nitrogen metabolism in the the vine. Aminoacetophenone, or 2-AAP, and two other compounds indole, and methyl indole related to the metabolism of the amino acid tryptophan are believed to contribute to this taint. It has been suggested that under certain grape growing conditions, the berry may accumulate excess concentrations of these compounds in a bound, glycosilated form. The bound glycosides may be hydrolyzed or broken, thus releasing the free, odor active volatiles into the wine and producing the taint.

The problem appears to be related to insufficient assimilable nitrogen. Initially, most of the tainted wines were reported from early harvest fruit (sparkling wine cuvees) and high yielding vineyards. Both early harvest and light pressing, as occurs with sparking wine production, can significantly lower the assimilable N. Riper fruit and higher press pressures increase the extraction of nitrogen. High yielding vineyards have a tendency to produce fruit with lower levels of assimilable N . The problem occurs more frequently in dry years and from vineyards with low levels of nitrogen. In dry years, nitrogen uptake is dramatically reduced. Unfortunately, the problem has not been resolved by nitrogen fertilization in the vineyard or the addition of diammonium phosphate to the fermenter.

It appears that the precursor of the atypical aging phenomenon result from breakdown products from a plant hormone produced in the shoots. The high nitrogen and antioxidant capacity of seems to protect red wines from this problem, although it has been noted in roses.

If you believe that you have wines with this atypical aging phenomenon please let me know. We are evaluating commercial wines for the level of incidence in Virginia.

Winery Planning and Design Workshop. The Winery Planning and Design Workshop held February 14 was a large success. We accepted 135 attendees and still had a waiting list of over 30. We will likely have another program and those who were not admitted to the first program will be given registration preference. The manual for the workshop contains discussions on business planning, wine economics, winery design, winery layout, and gravity flow etc, and will soon be available. Check the web site for details.