The destemmer removes the stems, the crusher breaks open the berries to release the juice without squashing the pips, which can contribute bitter flavours to the wine.
Modern wine-making methods have been greatly influenced by the ability to control fermentation temperatures. Sometimes, especially when the grapes have been picked in the heat, it is beneficial to cool the pulp in a heat exchanger prior to fermentation. This helps to slow down the process of oxidation so that fresh flavours are retained and fermentation does not start too soon.
There is a range of different types and sizes of press used to separate the wine from the solids but most modern ones are pneumatic, allowing the winemaker to control the pressure and avoid extracting bitter flavours from the seeds or skins.
The grape juice is generally left to settle to allow suspended solids to drop to the bottom of the tank, so that the juice is very clear. Sometimes enzymes are added to speed up the process.
Fermentation vessels vary enormously in size, shape and material depending on the type and quantity of wine being made and the resources available to the winery. The yeast needed for fermentation may be selected from commercial preparations and inoculated or, less commonly these days, fermentation may start spontaneously thanks to ambient yeasts in the winery and on the grapes.
Some top quality white wines, especially those made from non-aromatic varieties such as Chardonnay or Sémillon are fermented in small oak barrels (often as small as 225 litres), generally to impart flavour from the wood but also to increase the complexity of the wine through gentle oxidation. As with the maturation of red wines in oak, the smaller and newer the barrel, the more oak flavour is imparted.
Most white wine is made in large, inert, enclosed stainless-steel tanks. For modern, fruit-dominant wines, it is very important to be able to control the fermentation temperature, which is lower than for red wines.
When alcoholic fermentation is complete, malolactic fermentation may follow, thus converting harsher malic acid into softer lactic acid. 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.
Fresh white wines made for early drinking are generally fined with a fining agent to ensure the wine remains clear after bottling. They may be kept in the holding tank, protected from oxygen with a blanket of CO2, until the wine is needed for bottling. They are also chilled to almost 0°C to precipitate out tartrate crystals. These are harmless but if they are not removed they may form in the bottle and they can be mistaken for little bits of glass.
Top-quality white wines are often matured as well as fermented in oak. During maturation, it is common practice to stir the yeast sediment (known as lees stirring or bâtonnage) to impart a richer, creamy texture to the wine.
Almost all white wines are filtered to remove any bacteria that might spoil the wine after bottling, this is especially important for whites that are not bone dry.