of the Crabtree effect. The remaining oxygen is gradually sparged from the must by carbon dioxide. In some red wine processes, the addition of oxygen early in fermentation is an advantage because it assists the development of colour, mouthfeel, and flavour, in part by the oxidative production of acetaldehyde by yeast and the polymerization of phenolic compounds. A recently fashionable technique is the French process délestage. The main strategy for délestage is to transfer red must from one tank to another in order to maximize oxygen pickup during the vigorous stages of red fermentation. The more conventional red fermentation strategy is to submerge the floating cap of skins that is swept to the wine surface by escaping carbon dioxide. If the cap is allowed to dry out, there is a risk that the sugar level on skin surfaces will drop low enough that spoilage bacteria can infest the skins. When this happens, ethanol is further oxidized to acetaldehyde and then to acetic acid.


Oxygen can penetrate between the interstices of the floating skins. If the skins are allowed to become too dry, a red wine can be irreversibly spoiled at this stage of the process.


The series of biochemical reactions which occur in the absence of oxygen are described as reductive. In the absence of sufficient amino nitrogen to nourish the growing yeast population, some of the yeast cells die and release their cell contents. The sulfur containing amino acids cysteine and methionine from yeast cell protein can be reduced to hydrogen sulfide and further reacted to produce various mercaptans and sulfides. All of these compounds have noxious odours that we would rather not have in the wine. In addition to adding amino nitrogen, the noxious odors will likely go away if we add (you guessed it) oxygen.


There is a long series of reactions that affect wine character at each stage of production. All of them are affected by the appropriate presence or absence of oxygen. For example, in addition to extracting oak tannins and flavour compounds from oak barrels, barrel aging contributes minute amounts of oxygen that pass between the staves.


A modern, more controllable, and less expensive way of treating wine


with oxygen is called microoxygen- ation, or microox, in winemakers’ vernacular. Carefully measured amounts of oxygen or air are dispensed into the wine. The dissolved oxygen content of the wine is measured and the progress of oxidation of wine tannins is tracked. The overall effect is that a carefully treated red wine can be brought to market a year sooner than a barrel aged wine.


Sulfur dioxide removes oxygen from


wine in the tank and in bottle. Its use, which can be traced back to Roman winemakers, is to maintain wine in an appropriately reductive state at each stage. Without this material, there is a high risk of contamination with spoilage bacteria and the loss of fruity flavours. So where do we stand with the presence of oxygen during winemaking? It depends . . . — Gary Strachan can be reached at gestrachan@alum.mit.edu .


Proud Distributors of Rack & Maintenance Source All Rack & Maintenance Source racks are made to handle Burgundy, Bordeaux and American Barrel shapes. All standard order racks have four crossbars to maximize strength and safety. The one exception to this is our two barrel half-rack or bottom rack.


GERARD’S EQUIPMENT LTD. 33684 Highway 97 South, Oliver, BC


(250) 498-2524 or (250) 498-6231 • Fax (250) 498-3288 Producers


 Chardonnay  Dunkelfelder  Foch  Gamay


 Baco Noir  Cabernet Franc  Cabernet Sauvignon


rs of Quality


 Gewurztraminer  Malbec  Marsanne  Merlot  Mourvedre  Muscat Ottonel  Orange Muscat


 Petite Verdot  Pinot Blanc  Pinot Gris  Pinot Noir  Riesling  Sauvignon Blanc  Sovereign Coronation


MORI VINES INC. CONTACT: R.R. #3, 1912 Concession 4, Niagara-on-the-Lake, Ontario L0S 1J0


Phone: (905) 468-0822  Fax: (905) 468-0344 email: morivines@sympatico.ca


British Columbia FRUIT GROWER • Winter 2011-12


Ron Fournier, Oliver, BC


(250) 498-3350 29


 Seyval Blanc  Shiraz  Syrah  Vidal  Viognier  Zinfandel  Zweigelt


NOTE: These vines are Canadian made!Many different clones are available. Rootstocks available are Riparia, S04, 3309 and 101-14.


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