Over the next few weeks we will be looking at wine production techniques.
Today we’re focusing on the production of white wine.
Two factors determine if a white, red or rosé is produced: whether the grape does or doesn’t have colourants and the duration of contact between the grape juice (known as must), and the grape solids, including the skin or film. This process of contact is known as maceration.
White grapes with colourless pulp and skin are always used to produce white wine. Only the must will be used for fermentation without maceration.
Red, white and rosé can be made from these grapes. To produce a white wine with these grapes there must be no contact with the skin. If there is brief contact the wine will be rosé and if there is prolonged contact the wine will be red.
Only red wine can be produced with these grapes whether or not maceration takes place.
It’s a delicate operation producing white wine and growers will go to great lengths to ensure the grapes move from vineyard to winery without being damaged. They achieve this by harvesting by hand and packing the grapes in boxes rather than large containers.
The grapes are de-stemmed, as these can lead to a bitter taste, and lightly crushed just enough to break the skins without crushing the seeds. The crushed grapes may then undergo a short maceration process if the winemaker wants to extract some flavours from the grape skin. Otherwise the crushed grapes are pumped into the wine press.
Pressing extracts all the juice from the grapes. This is a very delicate process as the winemaker wants to avoid crushing the seeds and it must also be done at a low temperature to prevent fermentation from starting early. It must also be done quickly to avoid the juice oxidising.
After pressing the juice is likely to contain some sediments so the winemaker will leave the juice in tanks at a temperature of 0c to prevent the onset of fermentation while the sediment falls to the bottom of the tank.
At this stage it is not uncommon for sulphur to be added. Sulphur prevents oxidation and the development of microorganisms.
The juice is poured into vats to ferment for one to four weeks. Fermentation can be stimulated with the addition of yeasts or fermenting juice from another vat. At this stage, it’s important to regulate the temperature of the juice. Kept at a low temperature the juice will take a long time to ferment resulting in a higher quality wine. Fermentation can be speeded up by maintaining a higher temperature but this leads to an inferior wine that has a ‘cooked’ flavour.
Many winemakers opt to ferment in stainless steel vats as it’s easy to regulate the temperature but some winemakers choose to ferment in vats made from wood, concrete, or even plastic.
Now that the fermentation process is over the winemaker needs to separate the wine from the sediment, which consists mostly of yeast that’s completed its task. To do this the wine is carefully poured out of the vats leaving the sediment at the bottom. This process may be completed several times during maturation, which we’ll cover in another issue.