Making wine

Here's an interesting fact: turning grapes into wine is entirely natural and can occur without any human intervention at all. If grape juice comes into contact with airborne yeast it will ferment. Easy, isn't it?

Well, no, not really - which is why many modern wineries look like space-age facilities, gleaming with stainless steel tanks and industrial equipment of all shapes and sizes.

Receiving Grapes

Because grape juice is colourless, all the colour in red and rosé wines comes from the skins. There is therefore a difference between how white, red (and rosé) wines are made. Strangely it is even possible to make white wine from black grapes (such as when making Champagne).

For white wines, the grapes are pressed to separate their juice, known as must, from the skins and pips as soon as they arrive at the winery, while for red and rosé wines the skins and pips are retained. There are all sorts of different presses for this job, from picturesque wooden "basket" presses, to sophisticated machines that use a slowly inflated rubber balloon.

The juice and skins may only remain in contact for a few hours at a cold temperature for pale rosés, or for many weeks (until after fermentation has finished) for serious reds, allowing time for the skins' colour and other flavour components such as tannins to infuse into the wine. There are a number of techniques to control this extraction, such as pumping juice over the floating "cap" of skins, holding or pushing the cap down into the juice, or agitating it with panels. The skins may even be pressed afterwards to extract even more tannic structure.

Fermentation

Without rehashing school science lessons, fermentation is a chemical process where yeast turns the sugars in the sweet grape juice into alcohol and carbon dioxide. The yeast may be naturally occurring on the skins of grapes and in the air, especially in areas with long traditions of winemaking, or a specific yeast culture added by the winemaker for a more reliable and predictable process.

Winemakers may choose to control the process in a number of other ways. Fermentation generates heat, which speeds up the extraction of colour, tannins and flavour from skins and pips in red wines but can also affect the delicate aromatic compounds in the juice. Winemakers usually try to reduce the temperature, especially when making white wines, to preserve these aromas.

Some high quality wines are fermented in expensive oak barriques, the small barrels naturally regulating temperature as well as imparting some oak flavour to the finished wine. A much more variable process, this needs careful monitoring to make sure everything works to plan and is usually therefore only used for luxury wines.

Maturation

Fruity white wines are then ready for filtering and bottling, but for many serious wines a further maturation process is begun, sometimes lasting several years, and usually done again in oak barrels. Oak is a great material for ageing wine because it is not completely airtight and allows a very small amount of oxygen to interact with the wine. This softens wines and can add complexity, especially over a long period of time. The style of wines such as red Bordeaux and Rioja depend on this.

However, oak can also add its own flavours to the finished wine, and controlling this is one of the most important (and occasionally controversial) decisions for the winemaker. The level of oak flavour depends on a number of factors; newer barrels impart much more oaky flavour than those that have been used a number of times; barrels are "toasted" to different degrees; the wine can be "racked" from barrel to barrel with differing degrees of regularity and there is even a difference between American and French oak.

Other Techniques

The list of other variations and optional treatments that winemakers can use is mind-boggling. They could micro-oxygenate the must, use a reverse osmosis machine, or ferment using carbonic maceration. They will almost certainly fine the wine, and they may or may not filter it. Some may even pasteurise their wine. All may have very small, but perceptible, affects on the wine.

However, worrying about the minutiae of the winemaking process is not the best way to appreciate wine – by far the most important aspect is the end result, how it tastes.