Grapes go through many stages before they become the magical, delicious liquid we know as wine, and decisions made at every step of the winemaking process, including while the fruit is still on the vine, can affect the final outcome.
The weather before the grapes are picked and their ripeness are important; ripeness determines the sugar levels, which in turn affect the final potential alcohol content of the wine.
Sun is good – it reduces the amount of moisture inside the grape, thus concentrating the sugars. Rain just before picking is bad because the roots soak up the moisture, which is then passed into the fruit, watering down the sugars.
Rain can also affect the outside of the grape by making it mouldy or washing away the natural yeasts (needed later for fermentation) on the skins.
Once the grapes are picked, the clock starts ticking. The longer it takes for the grapes to be pressed, the greater the chance of the wine taking on bitter notes, as the natural yeasts on the skins may start to ferment prematurely.
How the grapes are pressed can affect the end results. White-wine grapes need to be pressed quickly and gently to retain as much freshness as possible; waiting too long will make the juice cloudy. The best pressing method for white-wine grapes is a pneumatic press – the grapes go in one end of a tank and a balloon is slowly inflated inside, which gently compresses the grapes.
Red-wine grapes are not as fussy about how they are pressed, as the skins need to stay in contact with the juice. The hue and the concentration of aromas and flavours depends on how long the juice is left in contact with the skins and stems.
Stems are another factor. For those winemakers who can afford to do so, removing the stems (some or all) helps to reduce tanninsand produces a smoother sip in the glass. De-stemming is especially popular in Burgundy, in the production of the French region’s pinot noir.
During the fermentation process, wine changes from one moment to the next, and one must watch it to ensure that it doesn’t “overcook”.
To do this, a winemaker has a number of tools on hand. He or she can control the fermentation by using stainless-steel tanks equipped with temperature coils (much like a kettle). Another option is to ferment wine in oak barrels to give it more flavour.
The winemaker could choose to kick off the fermentation using a special yeast culture to make sure the juice gets off to a good start.
Oxygen is fuel for fermentation; if the vessel holding the liquid is enclosed or otherwise covered, this affects how quickly the wine will ferment. For white-wine grapes, such as New World chardonnays, a secondary fermentation can be encouraged to occur where the natural malic acids (the tart and sharp characters in the fruit) are converted to lactic acid (soft and mellow).
This is all done by naturally occurring yeasts that go into action after the primary fermentation, giving the wine a slight buttery style (think California chardonnay).
When all the sugars that were in the grapes have been “consumed” and turned into alcohol, the fermentation is done and a wine is born. All the yeasts are now spent and settled on the bottom of the fermentation vessel. If a secondary fermentation is not desired, the winemaker will separate the lees (the spent yeasts) by racking the wine to keep it clear of sediment.
The wine can be aged in stainless steel, concrete or oak. Stainless steel and concrete prevent oxidation and do not add flavour to the wine. If the winemaker chooses to age in oak, which does add flavour, he must select the kind of barrels and the degree to which the interiors are toasted.
Lightly toasted oak gives the wine a hint of vanilla, but if the barrel is toasted to almost burnt, the wine will have lots of vanilla, and possibly piña colada notes (if it’s a white), or, if it’s a red, lots of pucker-up tartness.
Winemaker Dominique Portet, in Yarra Valley, Australia, describes his use of oak barrels as similar to a chef’s seasoning of a dish: it’s used to gently influence a wine so it turns out the way he imagines it should be.
How long should wine be aged? That all depends on tradition, wine rules and the winemaker’s preference. The youngest is beaujolais nouveau, which can be in your glass within six weeks of harvesting. Among the longest aged is a gran reserva rioja, which spends two years in the barrel and three more in the bottle before the winemaker is allowed to sell it.
Source & Author Credits: https://www.scmp.com/magazines/post-magazine/food-drink/article/2129488/what-goes-making-great-wine