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p r a c t i c a l w i n e r y & v i n e ya r d a U G U S t 2 0 1 4 67 W I N E M A K I N G of wines while reducing the concentration of negative sulfur- like off odors and volatile acidity. 16 Recent advances in the understanding of how proper rehydra- tion of yeast can lead to enhanced volatile production has led to further improvements in overall aromatics of white wines. The observed increase in concentration of 3-mercaptohexan- 1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) may reflect a chemical or biochemical change in the media, leading to a greater stability of the thiols or enhanced bioconversion of the cysteine conjugates by yeasts. Recent advances in the under- standing of yeast metabolism have led to the development of specialized rehydration nutrients for the enhancement of posi- tive volatile thiols in white wines. 16 Very clear settling reduces the long-chain fatty acid content of grape must, which can lead to an increased production of volatile acidity by yeasts. 10 Volatile acidity (VA) formation is, among other factors, also related to the sugar concentration of the must. High Brix musts have been shown to increase intracellular glycerol production in early fermentation as an osmo-tolerance mechanism in Saccharomyces sp., which results in an ultimate production of acetic acid and an increase in volatile acidity mea- surements in the subsequent wine. Because yeast-rehydration nutrients are sources of sterols and long-chain fatty acids which strengthen the plasma membrane, they enhance the fermenting yeast's osmo-tolerance, that results in lower VA formation. Proper yeast nutrition is important during fermentation. The use of a complex yeast nutrient provides the yeast with optimal amounts of organic and inorganic nitrogen, vitamins and miner- als. Pantothenate is a very important vitamin in the yeast's sulfur metabolism, and despite the presence of sufficient nitrogen, a shortage in pantothenate can lead to the formation of H 2 S. 13 It also Importance of glutathione Glutathione is a tri-peptide found in grapes and wine. Glutathione levels can be quite variable in grapes. A signifi- cant part is usually lost during early grape processing. Glutathione levels fluctuate during production, as the com- pound can be absorbed by yeast and then released after fer- mentation. If the final glutathione level is low in a young wine, there may be rapid loss of fresh varietal and fruity aro- mas, and poor aging potential. Glutathione interacts with other juice and wine constituents such as SO 2 , wine phenolic compounds, ascorbic acid and copper. These interactions affect both glutathione concentration and total juice or wine antioxidant status. Monitoring glutathione Awareness of glutathione levels can be beneficial at all steps of the winemaking process to maximize white wine aroma and flavor, and prevent premature aging. • The glutathione content in grapes indicates their antioxi- dant potential, and can be influenced by many factors includ- ing soil nitrogen, vineyard practices and grape maturity levels. • Monitoring the change in glutathione level during pro- duction helps to pinpoint where in the process glutathione is being lost. • It can be beneficial to identify winemaking processes that boost glutathione release during and after fermentation, and increase the glutathione level in wine. For more information about glutathione, contact Eric Herve or Steve Price at ETS Laboratories, phone: (707) 963-4806 or info@etslabs.com. Terravant Wine company purchases close to 1,000 Oenotank maturation tanks to replace older barrels in the cellar. We asked key Terravant personnel the reasons for such a large move from barrels to the Oenotank program: "The Oenotanks are really helping to get a nice, palatable wine to market that much sooner." General Manager Randy Pace "The maintenance of Oenotank is very low. We have already started trials of some very high-end, expensive wines into Oenotanks. I am achieving the same qualitative maturation of the wine. The idea that we can have a 5 barrel lot of wine is one of the real attractive parts." Winemakers Travis Proctor & Anna J. Clifford "All the tastings have been positive. The cellar master tells us we have not had to top them off - positive time-saving stuff." Terravant has a number of tier 1 & 2 wines maturing in Oenotanks, but they also have the highest level (tier 5) in them too. Mention was made of a vineyard designated Pinot Noir from the Santa Rita Hills appellation that is being matured 20% in new barrels and 80% in Oenotank, with the intention to bring both elements together once maturation is complete. Cellar Master Dean Guzman "Oenotank has been great from a quality & efficiency standpoint - we have been coming through bi-monthly and just making simple sulfur additions. We haven't seen any ullage or film being created on the surface, not to mention the wines are coming out great - they are well rounded. The Oenotanks are really helping to get a nice palatable wine to market that much sooner." Terravant Wine Company, based in Buellton, Santa Barbara County, provides custom services including private labeling & custom design, shiner sales, bulk wines, custom crush & AP. Terravant selected Oenotank, made by Australian pioneer & market leader Flextank International Ltd (not to be confused with a similarly named USA company), after extensive research into available alternates. Terravant has the capacity to mature 288,000 gallons of wine in the nearly 1,000 Oenotanks purchased. Terravant also has on trial French oak staves & chips "Esprit du Chêne," specifically launched for use with the Oenotank. Staves are made to the same standard as premium barrels, being from 150 to 175 year-old oak trees mostly from the "center" region of France. The goal is an authentic simulation of oak barrel maturation, in combination with the passive oxygenation naturally delivered through the Oenotank wall. The picture to the left shows stacked Oenotanks full of maturing wine. OakTree Trading of Santa Barbara provided an innovative financing option for the Oenotank purchase. FIND OUT MORE: James Bateman, Sales Manager cell: 707-200-7838 • email: james@wineryproducts.com Visit the Oenotank website: wineryproducts.com Visit the Esprit du Chêne website: espritduchene.com Randy Pace, General Manager phone: 805-686-9400, ext. 205 email: randy@terravant.com Visit the website: terravant.com Tiaan Bezuidenhout, CEO cell: 415-717-1620 email: tiaan@oaktreerentals.com Visit the website: oaktreerentals.com Oenotank technology licensed by Flextank International Ltd. Article copyright: Roaming Gnome Enterprises & Terravant Wine Company Premium Staves. The Spirit of French Oak.