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WineEast kera and Hanseniaspora in the absence of sulfur dioxide can be abundant in must and juice at the beginning stages of fermentation (Zoecklein, 1995). These native yeasts are often associated with cold soak procedures of red and white wine varieties that can produce high levels of ethyl acetate and acetic acid as an off by-product. This ester has a distinctive spoilage odor reminiscent of nail polish remover. Growth of "Brett" in wines can express off-odor descriptors such as horsey, barnyard and medicinal. This yeast is usually associated with wood cooperage, and its taint production is linked to volatile phenols. Film yeasts such as Candida spp. and Pichia spp. form a chalky layer on top of stored wine when containers are not filled to capacity. They are associated with oxidative defects such as acetic acid, aldehyde and volatile esters of acetate. Benefits from dissolved oxygen in must and wine There are several critical times during the winemaking process that dissolved oxygen in must and wine can be beneficial. These include hyperoxygenation of juice or musts, the role of oxygen during initial fermentation and the use of the microoxygenation technique to soften and increase color stability in red wines. Hyperoxidation: In some cases, oxygen exposure in the must/juice (known as hyperoxidation) has been associated with stabilizing white wines from further browning oxidation during the vinification process, and it is believed to help extend the shelf-life potential of those wines. This enzymatic oxidation occurs in white wine must and juice devoid of sulfur dioxide (SO2), where certain phenol groups react with oxygen to produce yellow quinones. These compounds in turn react with more oxygen to yield brown-colored products that fall out as a precipitate and are racked off the juice prior to fermentation. This process stabilizes further browning reactions in wine from this source (Ough, 1992). The difficulty of this procedure lies in knowing the actual oxygen capacity of the must/juice related to the total amount of phenolic substrates present, the variation in enzyme activity and the proportion of phenolic components serving as substrates for enzymes. This can vary based on cultivar and vineyard (Boulton, et al., 1999). There have been mixed reviews from studies indicating the final effect on sensory evaluation of wines treated by the hyperoxidation procedure. Based on my experience, I consider hyperoxidation of grape juice to be slightly less delicate in expressing varietal character in sensory evaluation, and I believe more studies need to be conducted to examine the effect this procedure has on the shelf life stability of different white wine varieties. Also, this oxidative process is not implicated in oxidative reactions occurring in wine. Fermentation: Oxygen is also essential during the initial stages of alcoholic fermentation for healthy yeast propagation and fermentation profiles. Most of the dissolved oxygen occurs at grape crushing, pressing and racking, which can approach LIQUID NITROGEN DOSING Keep dissolved oxygen levels to a minimum with the new MiniDose • Designed to discrete dose up to 200 CPM • Compact size ideal for filling lines, mobile bottlers and R&D facilities The NITRODOSE® MiniDose system is sold only through Vacuum Barrier and their select group of worldwide distributors Tel 1-781-933-3570 Fax 1-781-932-9428 sales@vacuumbarrier.com www.vacuumbarrier.com Liquid Nitrogen Handling SPECIALISTS LIQUID NITROGEN HANDLING Specialists Since 1958 SINCE 1958 Win es & Vin e s AU GU ST 20 13 93