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Home | The Process | White Wine Making


White Wine Making

Below is a diagram that shows the major steps in making white wine.  The process is similar to red wine, with a few important differences.

Harvesting Grapes

As simple as it might sound, harvesting grapes is one of the most important decisions made by a winemaker.  The goal is to have the grapes at the ideal, that is to say peak of ripeness, while avoiding the hazards that abound – rainy season, winds, rot, and vineyard pests.  The winemaker determines sugar levels determined using a refractometer, a field instrument that measures Brix.

Brix is a unit of measure where one gram of sugar in 100 grams of liquid equals one degree Brix.  In the vineyard, samples from different grape bunches are tested, being careful to take grapes from both sides of a vine, different parts of the vineyard, and shaded versus non shaded areas.  Grapes are typically harvested at Brix levels between 20 – 26 degrees depending on the variety, meaning the grapes are ripe and are roughly 25% sugar – the key ingredient in alcohol production during fermentation.



Once the decision is made to harvest, grapes can either be picked by hand or by using a mechanical harvester.  Hand picking is a tedious task, using sharp knives to selectively cleave ripe bunches and place them in “lugs”, rectangular stackable plastic containers.  Hand picking is considerably more costly than mechanical picking however hand picking of grapes allows for only the best bunches to be selected, and less damage is done to the grapes during handling.

Mechanical picking has one major advantage – cost.  According to the Wine Business Monthly, a mechanical grape harvester, in one hour, can harvest the equivalent of 10 hand pickers in a full day.  A mechanical harvester basically shakes the vine until the grape bunches are dropped to a conveyer belt.   Harvesters can run 24 hours a day and it is easier to pick at night in hot climates.

Crushing

Once the grapes are in the winery there are several steps before beginning the fermentation process.  The grapes are kept cool and these steps are accomplished quickly, as grapes begin to deteriorate soon after picking.  Sulfur may be added to the grapes as sulfur reacts with oxygen to form Sulfur Dioxide, a poisonous gas that prevents the growth of yeast, bacteria, and can also reduce browning of the grapes.  It is this addition that is responsible for the “Contains Sulfites” label on many wines.

Grapes are sorted by hand to remove debris from the harvesting process as well as grape bunches that are not ripe or otherwise undesirable.   The grapes may go through a mechanical crusher–destemmer that crushes the grapes releasing the juice and leaving the stems behind.

Pressing

Increasingly popular in wine production is the use of a mechanical press, a machine that accomplishes the same tasks as a crusher–destemmer with less impact on the grapes.  A press is a pneumatic device that basically fills a membrane (think balloon) with air or water and as it expands, it presses the grapes against a

Photo Courtesy of of ATI S.r.l.
Photo Courtesy of of ATI S.r.l.
perforated (think colander) exterior allowing grapes and skin solids to pass through while stems and seeds remain behind.  Grapes may be pressed one or more times.  The advantages of a press are considered to be the gentler handling of the grapes, less risk of crushing seeds or skin cells.  Once the press is complete the residual material left behind in the press called pomace, may be used to produce Grappa, however, is more likely to be plowed back into the vineyard.

Must Adjustment

Before starting fermentation the wine maker will evaluate the juice or “must” and determine if it needs to be adjusted to produce the desired outcome in the wine.  Two conditions can exist in the juice, either too little acid, or too little sugar (which will result in too little alcohol in the finished wine).  Must adjustments are the subject of much controversy and in much of the old world are heavily regulated or outlawed all together.  In the New World however, must adjustments are very common.
Acidification (adding acid) is practiced in warmer climates, where the amount of acid in grapes subject to a longer growing season tends to be lower.  Tartaric acid is added to the must to increase acid levels to enhance flavors and produce a more balanced wine.

Chaptalization is the process of adding sugar to the must.  Chaptalization is common in cooler regions where grapes may struggle to reach full ripeness, and hence sugar levels.  Insufficient sugar results in lower alcohol in the finished wine.

Once must adjustments are complete, the liquid is filtered to remove unwanted skin solids either by using a clarifying additive such as clay, or through the use of a centrifuge. 

Fermentation

The juice from the grapes is placed into tanks where fermentation will occur.  Fermentation is the transformation of sugar to alcohol enabled by the presence of yeast.  Fermentation begins with the addition of one or more yeasts into the clarified must (inoculation).  The yeast multiply and quickly begin to consume the sugar (glucose and fructose) and convert it to alcohol (ethanol).  The process yields heat and carbon dioxide as by-products and uncontrolled fermentation can produce bubbling and foaming vats of fermenting juice – one possible theory for the origin of the term “spirits”.



The fermentation may take place in large stainless steel tanks, large oak vats, or smaller oak barrels depending on the style the winemakers is striving to achieve.  Fermentation of white wine takes place at much lower temperatures than red wine, usually 58 – 65 degrees Fahrenheit (15 – 18 Celsius).  Cool temperatures are required to preserve the delicate fruit and floral flavors representative in many white wines.

Fermentation lasts for several days to as long as two to three weeks.  Fermentation ends when either all of the sugar has been converted to alcohol, the alcohol levels get so high as it kills the yeast, or the winemaker stops the fermentation to preserve a small amount of residual sugar in the wine.

Once the primary fermentation is complete, a secondary “fermentation” known as malolactic fermentation may be started.  Technically not a fermentation at all but rather a bacterial transformation, malolactic fermentation converts malic acid to lactic acid giving white wine a smooth buttery flavor.  Uncommon with crisp delicate whites, malolactic fermentation is popular with many Chardonnays.

Upon completion of fermentation, the winemaker continues to have considerable influence over the style of the resultant wine.  After fermentation the wine may be allowed to remain in the fermentation tank staying in contact with the dead yeast, known as “lees”, and represented on many bottle as “sur lees”.  This allow flavors from the yeast to be imparted to the wine.  The process of clarification involving fining or filtering removes suspended material from the wine.  While not common, some winemakers are forgoing the step, under the premise that “unfiltered” wine as it is known, is richer in flavor.

Aging

Depending on the wine, aging may be non-existent or last several years.  Most white wine spends little time aging and is ready to drink early; some wines derive benefit from aging in oak barrels which can add the flavors of vanilla, oak and toast.  Chardonnays are frequently aged in Oak barrels, as well as some Sauvignon Blanc (Fume Blanc from California), and occasionally even Pinot Gris.

 




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