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Winemakers are a funny lot. Some like nature to do most of the running while others aren't happy unless they are in complete control of everything. Some even get paranoid if they don't have full control of even the air around them. Let me explain.
For some wine styles, subjecting the wine to air during its making is punishable by death. Take Riesling for example. Great Rieslings are by nature, delicate fruity wines that have no hints of coarseness on the palate. Pristine freshness and maximum fruit retention is achieved by ensuring that the wine is not subjected to the oxidative forces of exposure to air. This is achieved by constantly protecting the wine under a blanket of inert gas such as carbon dioxide while it is being made and stored. This shroud of gas helps ensure that the dissolved oxygen level of these wines are kept to a minimum.
It's another story at the opposite end of the style spectrum; the full bodied dry red wine. Here oxygen is an ally, helping to enhance the structure of the wine. Most young red wines contain a large amount of red coloured material extracted from the skins during ferment. Called anthocyanins, they make red wines red. However, by their nature anthocyanins are a pretty unstable lot. They tend to want to react with other things and fall out of the wine, making it lose its colour. Anthocyanins also readily react with the wine preservative sulfur dioxide (SO2) which is routinely added to most wines. When this happens the anthocyanin is effectively bleached.
Here's where oxygen comes in. In the presence of oxygen, anthocyanins readily chemically combine with tannin molecules. These complexes are also coloured but unlike free anthocyanins they are very stable and are resistant to bleaching. In the presence of dissolved oxygen the smaller tannin molecules themselves also join together to form long chain tannins. These are softer, more supple and far less bitter than the small tannins from which they were built. Winemakers call this process polymerisation, and it obviously encouraged wherever possible in full bodied styles.
So if air is important to the polymerisation of tannins, where does it come from? In a natural approach used by winemakers for centuries, red wine has been exposed to air during winemaking simply by 'slopping' it around. Pumping it up and over the fermenting juice, and by pumping from barrel to barrel (called racking) are winemaking steps which as an aside help oxygenate the wine. Winemakers may even intentionally just transfer it from one tank to another in order to give it a bit of a 'dust up'. In addition, the wine barrel naturally allows in air through the gaps in the staves, and through the bung-hole when the winemaker opens up the barrel to top it up with wine after some is lost through evaporation.
This uncomplicated approach has one draw-back. Its effects are slow, unpredictable and un-measurable. So come on in, one of the new big things in winemaking. Micro-oxygenation or Micro-ox. Micro-ox is a process whereby a high tech machine accurately doses a wine with oxygen in the form of micro-bubbles over a relatively short period of time. The principal behind the technology is that the dose rate of the oxygen dialled up by the operator of the micro-ox machine is the same or less than the rate at which the wine uses it up in undertaking all the polymerisation reactions. It is usually applied prior to malolactic fermentation (MLF) when the tannins and anthocyanins are more receptive to reacting with each other, and the sulphur dioxide levels are at their lowest (Winemakers generally allow the SO2 levels to fall at this stage to encourage the fermentation. This helps the process of micro-ox as low SO2 levels favour polymerisation).
Many wineries are trialling or using the process to improve the quality of their mid range wines. The process appears to bring together wines which have been fortified with added tannin and pressings. As micro-ox can be made to mimic (at least in some ways) the slow oxidative nature of barrel maturation, other winemakers are experimenting with giving wines oak character using oak alternatives such as chips and staves, and then micro-oxing them in tank to build in the structure. Cheaper than barrels and a lot quicker too.
Others are considering micro-ox as a labour saving device. The process of transferring wine from barrel to barrel to aerate it is a very labour intensive task. Barrel based micro-ox may allow winemakers to avoid racking and hence save them money, both in labour costs, and in wine spillage, both of the accidental type and in the 'controlled' type that has been perfected by a few cellar-hands. (Don't worry lads, there's little or no need to micro-ox good tawnys and muscats).
In summary, micro-ox also gives the winemaker nearly complete control over the oxidative state of the red wines they make. Interesting philosophy I suppose. Some will rue nurture dominating nature, others will no doubt applaud the improved efficiencies and lower priced decent quality wines that will probably come of it. I think I'll keep out of this one.