Making White Wine

As soon as possible after picking, the freshly gathered white wine grapes are taken to the presses, thus avoiding any oxidisation of the grapes as they sit on the trucks, exposed to the sun and air.

They are fed into a crushing machine that gently splits the skins. For most white wines, it is not desirable to allow the skins to be in contact with the grape after crushing, so the skins and other grape matter are quickly separated out from the juice. However, in making some of the great white wines of the world, the skins are allowed to remain in the juice for a day or so in order to lend additional body and character to the wine.

A juicing machine uses pressurized sulphur dioxide gas to gently squeeze out the juice, which then goes to a settling tank, where undesirable solids such as dirt and seeds settle to the bottom.

At this point, the winemaker may think it necessary to doctor the grape juice, adjusting the acid or sugar levels. Calcium carbonate may be added to reduce acidity, and tartaric or other acids may be added to raise it. In cooler regions, where even white-wine grape varieties struggle to ripen, sugar may be added to the juice to allow the wine to reach the right alcohol level. This is called chaptalization. The sugar and acid must be in balance at the desired levels in order to make good wine.

Fermentation

Although wine yeast naturally accumulates on grape skins during the growing season, almost all winemakers introduce carefully cultivated yeast to the juice, so that the fermentation process can be carefully controlled. A slow fermentation is desirable for a number of reasons. If the fermentation proceeds too rapidly, the temperature might be raised to a level that prematurely kills the yeast. This would produce a rather rough and unbalanced wine. Also, the yeast itself imparts character to the wine, so a slow fermentation, which allows longer contact with the yeast, is beneficial.

High quality white wines require long, cool fermentation (at around 15 °C) to allow flavours and complexity to develop. Most winemakers control the temperature of the fermentation by refrigeration and recirculation. The carbon dioxide that is produced during fermentation is permitted to escape from the enclosed vat without allowing ambient air back in.

When alcoholic fermentation is complete, malolactic fermentation may follow: converting harsh, acidic malic acid into softer lactic acid. This process, like alcoholic fermentation, occurs naturally but is usually controlled by the winemaker. However, for many white wines, especially those made from aromatic varieties such as Riesling or Muscat, the malolactic fermentation is blocked as the fresher acidity is an attractive component in the wine style.

Settling and Maturing

Once fermentation is complete (taking between 1 and 4 weeks or so) most white wines are considered complete. The wine is run off into stainless-steel tanks for a period of settling, with a few months of ageing allows the flavour components in white wine to become more harmonious.

The alternative to stainless-steel tanks is to mature the wine in small oak casks (often referred to as 'barriques' - the original Bordeaux name). Maturation in oak is much more common in red wines, but Chardonnay and Semillon in particular seem to work well with the unique vanilla and buttery flavour that oak imparts to wine. Because of the long history of wine storage in oak, these flavours have become accepted as basic components. Now that less expensive storage vessels are available, such as those made of stainless steel, oak flavour is an additive of sorts. In fact, some producers of inexpensive wines circumvent the great expense of oak barrels by adding oak chips to wine held in stainless-steel tanks. Whilst tasty, these wines are rarely subtle or sufficiently well-balanced for ageing and further development in bottle.

Clarifying

Finally, the wine must be clarified to leave it crystal clear for bottling. This process can be carried out by one of a number different methods:

• Filters and centrifuges can be used to eliminate all solid matter, although some people claim this can also remove body and character from the wine.
• Fining uses a gelatinous substance that is stirred into the wine. The fining agent gradually sinks to the bottom of the barrel, dragging all the undesirable particles with it. Traditionally, fining is done with whisked egg whites. Other common substances are: bentonite clay, casein (milk protein) and isinglass (made from fish bladders).
• Racking is a relatively passive means of clarifying wine. If the wine is left undisturbed, the heavier unwanted particles eventually sink to the bottom. The clear wine may then be 'racked', that is, drawn off to another barrel.
• Cold stabilisation is a relatively harsh treatment used to clarify inexpensive wines. This process involves chilling a tank of wine almost to freezing point. At this low temperature, tartaric acids naturally present in the wine are forced to form into tiny crystals. These crystals can then be removed during filtration.

Resting

Virtually all wines benefit from a resting period in the bottle. Although red wines generally undergo a much more gradual evolution in the bottle than do white wines, a well-made white wine can improve for five or more years in the bottle. Chardonnays and Rieslings are known to age more gracefully than other white wines.