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Wine Production

Wine Production

wine making with grapes

Wine production is the process of fermenting the natural sugars in the grapes and converting them to alcohol. Depending on the grape variety, region, climate, vintage, grape quality and choices made by the winemaker, the wine produced will be unique. This is what makes wine both confusing and also so enjoyable.

Below outlines the basic process of making both white and red wine. Each decision that is made, both in the vineyard and also in the winery, will influence the end wine. By learning more about wine making, you will begin to understand more about the personalities of the winemakers themselves, their stories and also their beliefs.

There are several key differences in how white and red wines are produced. The main difference is that with white wines, the skin of the grape is removed before fermentation to reduce tannin extraction and bitterness. With a red wine, the skin is left in contact with the grape juice during fermentation to extract colour, flavour and tannins.

This creates the other main difference, which is that white wines can be fermented in both stainless steel tanks and oak barrels whereas red wines can only be fermented in large format tanks made from stainless steel or concrete. This is because it is too difficult to remove all the skins from an oak barrel after fermentation.

White Wine Production

The grapes are picked either by hand or machine when they are considered to be ripe by the winemaker. Ripeness is defined by both the balance of sugar and acid in the grape and also the flavour ripeness and complexity of the fruit.

The grapes are transported to the winery where they are usually destemmed and / or crushed and then pressed to separate the juice from the unwanted skins. In some cases, there might be a short period of skin contact or pre-fermentation maceration for several hours to extract a small amount of colour, flavour and tannin from the skins.

Alternatively the grapes may be whole bunched pressed – that is, neither destemmed nor crushed, and then placed directly into the press. This is done for sparkling wines, certain styles of premium white wines and also when the fruit is overripe as the stems help to separate the juice from the skins.

After pressing, the wines are clarified to remove any solid particles as this can give the wines unpleasant cardboard-like flavours. Juice clarification either happens overnight in a cooled tank with the solids settling to the bottom of the tank. Alternatively the juice can also be filtered or put through a centrifuge.

At this stage, commercial wine styles may also have some additions or adjustments made to them, such as:

a. Acid addition – if the acid is too low
b. Deacidification – if the acid is too high
c. Sulfur Dioxide – to protect the juice against microbial activity
d. Fining agents – such as bentonite to decrease off flavours and help clarify the wine
e. Nutrients – to provide an adequate nutritional base for the yeast
f. Wood – the addition of wood shavings, chips or staves instead of fermentation in oak decreases costs
g. Sugar – this is illegal in Australia but is legal in Europe and other countries where the weather is cooler and the grapes may not ripen fully 

The winemaker can choose whether to ferment the juice in stainless steel tanks or in oak barrels. The choice depends on both the desired wine style or on price as oak barrels are expensive. Generally speaking when making premium wine, aromatic white grape varieties such as Riesling, Sauvignon Blanc, Gewurztraminer, Sauvignon Blanc and Moscato are fermented in tanks to maintain varietal purity and freshness.

Non-aromatic grape varieties such as Chardonnay are fermented in oak barrels to give the wine texture and flavour complexity. Oak barrels mostly come from France and the USA. French oak has a finer grain and gives the wine a vanilla character. Oak from the USA has a coarser grain and gives the wine a coconut character. The oak barrel is also toasted before filling and this imparts a toasty, charred, burnt character as well as other oak derived flavours such as licorice, nutmeg, cloves, sandalwood, cedar, chocolate, coffee and tobacco. Barrels may be new or old depending on how much oak flavour the winemaker wants in the wine. 

Fermentation is the process of the yeast converting the grape sugars into alcohol, carbon dioxide and heat. This can either occur due to the addition of yeast or ‘naturally’ due to ambient yeast that lives in the winery. Yeast addition gives the winemaker more control and certainty about the resultant wine whereas natural fermentation is said to give the wine more complexity.

Fermentation lasts for between seven days to over one month. Depending on the style that the winemaker wants to achieve, the wine can either be fermented at cool temperatures to preserve varietal aroma and freshness in the wine or at warm temperatures, which decreases varietal aroma.

Following primary fermentation the wine may be allowed to go through a secondary fermentation called malolactic fermentation (MLF), which converts the tart malic acid into the softer lactic acid. MLF also gives the wine additional flavour characteristics of butter, butterscotch or cheese.

If the wine is fermented in a stainless steel tank, it will be ‘racked’, which removes the dead yeast cells and other solid particles. It will also be stabilized to remove any protein haze or tartrate crystals, clarified and then stored in stainless steel tanks again until it is ready for bottling.

If the wine has been fermented in oak barrel, after fermentation the wine will be ‘topped’ regularly by wine to make sure there is no oxygen in the barrel that could result in the wine being oxidsied. The wine may also be stirred every week or two for several months to mix the dead yeast cells left over from fermentation into the wine, giving the wine more texture and yeasty, bready or ‘leesy’ flavours.

The wine is then racked off the gross lees (or solids) and stored in oak barrels for another 4 – 12 months. Finally the winemaker chooses the best barrels to go into the final blend, mixes them together in a tank and then bottles the wine.

Red Wine Production

There are several wine making options that the winemaker can choose depending on style and price. Cheaper wines tend to be machine harvested, destemmed, crushed and then fermented in large rotating fermenters to ensure that the skins remain in contact with the juice throughout fermentation to extract maximum colour, flavour and tannins.

In contrast, premium wines may be hand sorted on sorting tables to remove all unwanted leaves, stems and damaged or diseased fruit. The grapes can be then:

a. Neither destemmed nor crushed
b. Partially destemmed but not crushed
c. Destemmed but not crushed
d. Destemmed and crushed

Each method above creates a different style of wine. Fermentation with the inclusion of whole bunches adds textures and complexity to the wine but can also give the wine ‘green’ or unripe characters in cooler vintages. Whole berry fermentation suits lighter wine styles, such as Pinot Noir, as it adds flavour complexity to the wine. Destemming and crushing prior to fermentation assists with the extraction of colour, tannins and flavours however some winemakers believe that destemming and crushing can decrease the detail in the wine and decrease its ‘sense of place’ or unique vineyard identity.

Yeast and other additives may then be made – similar to white wines – and the must (the mix of skins and grape juice) may be cold soaked (macerated) for several days prior to fermentation to extract a more favourable combination of flavours, colour and tannins. Alternatively the wine may be allowed to start fermentation directly after picking or destemming / crushing.

Fermentation will last for between seven days and over one month. The wine is then pressed to remove the skins and stems and is either stored in stainless steel or in oak barrel whilst it undergoes the malolactic fermentation process.

Wines that have more tannins or are stronger in flavour are well suited to longer maturation periods in oak, whereas softer, fruity styles are better suited to maturation in tank.

After maturation the wine may be fined to remove excess tannins and bitterness, filtered to remove any unwanted microorganisms, stabilized, the acid adjusted and then bottled. However some winemakers who follow more natural winemaking principles will not make any adjustments or additions to the wines before bottling.

After bottling the wines need to settle for at least one month and some premium wines will not ‘open up’ for over one year after bottling.

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