dispensing into wine. There are many substances in wine


that consume oxygen: sulfite, ascorbic acid, lees, and phenolic compounds.


The guideline is that oxygen should not be added to wine at a rate which will increase the dissolved oxygen content. If the rate of oxygen utilization by the wine is exceeded, then undesired production of aldehydes, volatile acidity, and growth of spoilage organisms can occur.


In order to prevent the growth of spoilage organisms it is especially important to ensure that oxygen from microox does not accumulate in tank headspaces.


Typical systems are fed from a high-pressure oxygen cylinder which then feeds into a solenoid-controlled meter. The metered oxygen then flows through a small reservoir and into a diffuser mounted near the bottom of a wine tank


The diffuser should be placed above, not within, the lees. The tank volume is not especially important but the tank height must be at least 2.2 metres in order to provide sufficient time for oxygen to dissolve while the bubbles float toward the wine surface.


Diffusers range from sintered glass, ceramic, or stainless steel to the newer membrane based diffusers. A couple of intriguing new technologies include specially- designed polyethylene tanks which mimic barrel permeability of oxygen, and electrochemical microox which is mediated by electrolysis with glass carbon electrodes.


I look forward to testing the electrolysis system because of its simplicity and potential for fine electronic control.


Even though micro-ox has already been widely adopted, it is still controversial. Many contend that the method allows accelerated development of wine character with greater control than in oak barrels. On the other hand, it is contended that micro-ox is a method for the production of less expensive wines and the improvement of wines from poorer quality grapes. The use of micro-ox has a substantial learning curve because the composition of wines varies and


British Columbia FRUIT GROWER • Summer 2012 23


no two wines require the same amount of oxygen to optimize quality. During treatment, wine quality may actually decline and then recover until the wines achieve a “sweet spot” in which varietal aromas and tannin structure are optimized. If micro-ox is continued beyond that point, the wines develop oxidative aromas and tannin quality declines.


There are guidelines for each of the systems available commercially. Be prepared to study them carefully and don’t be surprised if your first batch doesn’t live up to expectations. Be sure to enlist someone with a really good palate to monitor progress. Take a deep breath before you start, then open the oxygen valve. — Gary Strachan can be reached at gestrachan@alum.mit.edu.


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