Phase 1 is usually avoided altogether by conventional winemakers because it requires intensive training and involves substantial risks for the unschooled. It also ties up tanks, increases the time required for aging, and often causes young wines to show poorly for a time.
Phase 2 work is done post malolactic (ML), just after SO2 addition, to refine and civilize tannins and partially quench reductive strength prior to barreling down. It is also effective for wines not destined for barrels, in conjunction with oak alternatives. This is the MOx most commonly employed in California, a far cry in its results from Phase 1. However much large wineries may wish to replace barrels with tanks by introducing oak alternatives and oxygen, tank-treated wines must also be given an opportunity to off-gas tanky aromas, a tricky problem that MOx does not address. It is my own custom to move wines to neutral cooperage after Phase 2 structuring.
Phase 3 is performed after barrel aging, when the wine may have become too delicate to continue in wood but still needs a tannin “haircut.” Commonly, the pithy, untoasted oak tannins of new barrels take a year or two of wine penetration into the stave to begin to extract, and thus can disrupt a maturing wine’s harmony at just the wrong time. A couple of months in tank receiving half or a quarter of a barrel equivalent can restore roundness and grace. Phase 3 is also employed to knock down reductive strength prior to bottling, particularly in preparation for bottling under screw caps, which do not supply a burst of oxygen as corks do by virtue of their compression when inserted.
MICRO-OXYGENATION’S THREE PHASES
Shopping Equipment
As with a kitchen appliance, picking out micro-oxygenation equipment begins with identifying your goals. The stove or food processor that’s right for you depends on whether you are Masa’s or McDonald’s.
That said, as winery expenditures go, MOx equipment is quite a bargain, topping out at about $2,000 per tank system. My advice is to buy the best. High-performance MOx gear is one of the best deals of any capital investment you can make for increasing quality.
The original MOx units were stripped-down experimental prototypes. These have proven inadequate for serious full-plant installations, where pennies saved in investment can cost many dollars of inconvenience. Today’s systems enable hyper-ox, macro-ox, micro-ox, cliqueage, and sulfide treatment, all from the same diffuser. Internet-based control panel displays can link to lab and sensory databases and fixed sensor inputs for temperature, dissolved oxygen (D.O.), and so forth, enabling adjustment and troubleshooting from any location, including your iPhone. That said, the wisest initial purchase is usually a high-end small unit on which you can build your skills.
Your key choice is the diffuser. For post-ML Phase 2 work, just to soften aggressive tannin for early release or to polish the rough edges imparted by an average-quality oak alternative, many wineries (foolishly, I think) choose a low-end model with a stainless diffuser. Bear in mind that this type of equipment is not suitable for pre-ML Phase 1 work for structure enhancement, color stabilization, and aromatic integration. For Phase 1 work, the tiniest possible bubble size is critically important. Membrane-type diffusers have the added benefit of providing a built-in continuous bubble-point integrity test.
Most large conventional wineries have already adopted Phase 2 MOx wholesale. If your intent is to produce clean, affordable wines in a factory setting, you probably know all you need to know about this primitive form of micro-oxygenation. Yes, tanks can replace barrels, and tannins can be softened using even the cheapest MOx equipment on the market. For you, the big news is that the experimental prototype systems of a decade ago have been replaced by professional plant-integrated systems that interface with your existing process control, lab, and sensory databases, placing the control panel on your browser instead of atop the catwalk.
But don’t kid yourself that this type of work reveals anything about wine’s nature. The skills involved in Phase 1 micro-oxygenation are entirely different from straightforward Phase 2 work. Thinking of MOx as a way to rush wines cheaply to market is like thinking of your Lamborghini as a really good flashlight. Which it is. But this misses the point of a high-performance vehicle.
Wineries that have turned the corner to postmodern methods generally place a premium on quality over image and are able to shift a few marketing dollars to skilled wine production labor to ensure that the winery’s credibility resides in every bottle. Any size is possible, even large volumes. Rule One is stay close to the wine. Rethink your assumptions, trust your senses over your theories, and go with what works. Because MOx is weird and counterintuitive, smart wineries generally budget for a bit of coaching from an expert for the first couple of years at least.
THE DEVIL IN THE DETAILS
Setting up for Phase 1 micro-oxygenation involves a fair degree of prior planning and adjustment of standard crush protocols. Treatment is ineffective when wines are cloudy or cold. Suspended particulates such as yeast and grape solids are powerful oxygen scavengers. Fortunately, a good diffuser run at 60 ml/L/month will often clarify a burly young Cabernet in forty-eight hours. Not so for a wimpy Pinot Noir, however. The rich get rich and the poor get poorer. ML suppression is important to maintaining clarity, so SO2 at the crusher is commonly bumped to 45–50 parts per million (ppm) to slow its onset.
FIGURE 5. Empirical temperature dependence of oxygen uptake reactivity.
It is pointless and dangerous to run oxygen outside the ideal range of 59–65°F. The engine of oxygenative structuring I mentioned above (Singleton’s vicinal diphenol cascade reaction, fully explored in chapter 6) is extremely temperature-sensitive, with reactivity plummeting by 70% at 50°F. That means a warm wine can absorb almost four times as much oxygen at 59°F as it can when chilled to 50°F (fig. 5). A single degree’s difference changes everything in a cellar. Here again, oxygen trials dramatically reveal essential information for winemaking in general, explaining, for instance, the common occurrence of volatile acidity in the cold cellars of Burgundy and Oregon.
Unless you have heatable glycol, keeping your tanks in the proper range is a challenge. Pumping through heat exchangers doesn’t work very well, as stirring up solids renders treatment ineffective. Drum heater belts are an inexpensive fix, able to hold a 4,000-gallon tank 15°F above ambient temperature with 1,000 watts of house current.
The lighter the wine and the farther the tannin/color ratio veers from 4 to 1, the trickier MOx treatment becomes. Big Cabernets and Petite Sirahs are easy to work, and often beg for it. Pinot Noirs should be avoided by beginners, and even Zinfandels tend to be very tricky. Blending in press wine is often very useful, and well-selected oak products can supplement deficient wines by providing cofactors as well as oxygenative phenolics (see chapter 4).
DRIVING WITH YOUR TONGUE
Ducournau developed a system for monitoring MOx treatment through frequent tasting. Sulfides or aldehyde are the primary indicators that the O2 rate should be adjusted up or down, supplemented by the openness of fruit expression. Tannin evolution is followed from green to hard to firm to round to melted.
FIGURE 6. Example record of micro-oxygenation of a 2000 Cabernet Sauvignon. Each column represents a day of treatment. Along with treatment rates and changes, sensory scores are recorded on a five-point scale. Excessive aldehyde suggests reducing treatment rate, while the presence of sulfides indicates the rate can be increased. Tannins evolve from green to hard to firm to round to melted. Diminution