Wines & Vines

WineEast Winemaking the saturation point at 6-9 mg/L depending on temperature, equipment and handling procedures. When musts lack oxygen, the fermentation process becomes slow and often stops to yield an unacceptable wine. After a few generations of yeast growth, sterols are initially used up and not renewed. Oxygen is critical to sterol synthesis and thus the successful completion of primary fermentation (Peynaud, 1984). The lack of oxygen can cause stuck or sluggish fermentations, resulting in typically dry wines being sweet on the palate in addition to potential yeast stress producing off by-products such as hydrogen sulfide. Essential concentrations of oxygen to fermenting must/juice exhibit levels near 4-6 mg/L at the beginning and end of yeast cell growth to ensure a successful finish to primary fermentation (Specht, 2010). A majority of the oxygen will be scavenged by the yeast cells or blown off by the production of carbon dioxide (CO2) during the fermentation process. Micro-oxygenation: Some controlled oxygen exposure also may be beneficial in select red wines during barrel aging by a cel- OAK ALTERNATIVES - BECOPAD Eastern Distributor for Beco Filter Sheets, Siha Yeast, EvOAK Oak Alternatives, Parker-dh Membranes, Chillers, N2 Generators, Zander Air Products R CENTRIFUGES 94 W in e s & V i ne s AU G U ST 20 13 - DECAN T E S TERILE FILTRATION - WATER FILTRATIO N - SIHA YEAST - lar procedure known as micro-oxygenation. This controlled process increases phenol polymerization, improves color stability and has the effect of softening the palate (reducing harshness) in red wines (Zoecklein, 1995). It is important to understand that micro-oxygenation is intended to avoid excessive accumulation of dissolved molecular oxygen, which causes oxidation in the must or wine (Smith, 2002). However, the advantages of micro-oxygenation need further research and should be performed by trained personnel only in recommending this technique. Oxygen elimination post primary and pre bottling Oxygen is generally understood to be detrimental to wine quality, especially from the end of fermentation through wine storage and bottling. The presence of oxygen after primary fermentation and during the latter stages of wine production can increase browning reactions, chemical and microbiological instability and result in the production of off-aromas such as acetaldehyde. Attention must be given during the cellaring process to avoid those potential sources for oxygen pickup and prevent excess oxygen from dissolving into the wine. Key sources for oxygen pickup include: racking, excess headspace, pumping, cold stabilization, filtration and bottling. Depending on temperature, dissolved oxygen levels can range from 6 to 9 mg/L in wine (Peynaud, 1984). Higher levels are expected at lower temperatures. Since the rate of oxidation increases with temperature, it is critical to add the appropriate amount of SO2 based on wine pH. Furthermore, when kept at low temperatures such as during cold stabilization, protecting the wine from air and keeping tanks full is essential to minimizing oxygen absorption (Gallander, 1991). When wine is moved in the cellar from tank to tank or barrel to barrel, it is vulnerable to increased amounts of oxygen dissolving into the wine. Consequently, it is vital to limit movement of wine as much as possible. Critical aspects regarding maintenance and the use of pumps and filtration equipment according to manufacturer's directions are essential in keeping excess oxygen from entering the wine during this time. Inspect for leaky pump Sparging with inert gas or liquid nitrogen seals, secure loose hose connections and make sure filter plates are tight to help minimize oxygen pickup. When racking, it is vital to purge all transfer lines/hoses with an inert gas such as nitrogen, carbon dioxide or argon to help displace oxygen. Prior to racking, it is recommended that the receiving tank or vessel be purged with an inert gas as well. It is good practice to rack from the bottom of one tank to the bottom of the receiving tank or vessel. Be sure to plan accordingly so there is no headspace in any tanks or barrels during wine storage. If any headspace exists, an inert gas blanket is vital to drive off the oxygen in the headspace. Another area of concern for excess oxygen dissolving into wine occurs during cold stabilization. Since oxygen dissolves into wine more readily at cold temperatures, it is essential to recognize this and make sure SO2 levels are up based on wine pH prior to cold stabilization procedures. Avoiding headspace during this process is also critical in protecting wine from oxygen absorption. Prior to bottling, excess oxygen in wines can be removed by using an inline sparger. This introduces an inert gas like nitrogen (N2) or CO2 through a porous stainless steel cylinder suspended in the wine. As the wine passes around the sparger, gas bubbles enter the product and displace the dissolved oxygen. The bubbles will rise to the top of the tank, releasing the inert gas and oxygen. For this procedure, the use of CO2 as an inert gas is less effective and may

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