White Wine Making
The term “white” loosely describes wines that range from nearly without color to ranges of straw, yellow, and gold.
Color in wine comes largely from contact between the grape juice and the grape skin. Hence, it is possible to make a white wine from the juice of a red grape if the winemaker prevents or minimizes skin contact. We will look into this phenomenon in the coming sections on rosé wines and sparkling wines, but for now, when we speak of white wines we mean white wines made from white grapes.
You cannot make a red wine from a white grape, but you can make a deeply colored “orange” wine from white grapes if you macerate the juice on the skins for a long period to extract whatever pigments are available in the skins of the light-colored grapes. When we speak of white wines we mean white wines made without this kind of maceration.
It is useful to highlight some of the general differences between the process that produces white wine and the process used to produce red wine that we have just covered.
- White wine usually ferments at cooler temperatures than red wine.
- We ferment white wine almost always in closed fermentation vessels while we may use open vessels for red wine.
- White wine is less likely to see oak aging that red wine, and if it is aged in oak, the aging is for a shorter period and with less aggressive oak.
- Nearly all red wines undergo malolactic fermentation to soften their acidity, but this is only done with some white wines.
- Most crucially, we press white wines to separate the juice and the grape solids before alcoholic fermentation but press red wines after alcoholic fermentation.
We begin in the vineyard. As with red wine, our goal is not to damage the grapes, so we use stackable plastic boxes to protect the grapes from being crushed by their own weight. It is also important to keep the grapes as cool as possible through the entire winemaking process, and so we might harvest at night under lights (which increases operational costs).
Next, as with red wine, we sort, de-stem, and crush the grapes. Unlike the red wine process, we then press the sweet pomace that remains to separate the juice from the solids. We want to avoid further contact between these solids and the juice to prevent phenolic compounds (so essential to the red wine process) from promoting oxidation in the more delicate white wine or adding unwanted astringency, unwanted amber or brown coloring, and other effects. Oxidation, which is widely tolerated by red wines, causes acetaldehydes to be produced which can compromise the aromas of the white wine. At this stage, also to prevent oxidation, we add sulfur dioxide (sulfites). Because white wines lack the antioxidants found in red wines (tannins, proteins, phenolic compounds), they generally require a higher level of sulfur dioxide than do red wines.
Some optional steps at this point involve:
- Chilling the juice
- Allowing the sediment to settle out of the juice
- In this step, the wine is bulk chilled in stainless steel to precipitate out tartrate crystals, which, though harmless, give the appearance of shards of glass when the wine is bottled.
Next comes the alcoholic fermentation process using ambient or cultured yeast. Most white wines are fermented in closed stainless steel vessels, often mechanically chilled, but an option, often chosen for high-end Chardonnay (the most popular of the white wine grapes) is to ferment in an oak barrel to add texture body and mouthfeel. It is important to distinguish barrel fermentation from barrel aging (a wine could be subject to both). Wines fermented in oak have less oak influence than wines aged in oak, with better integrated oak flavors and well-defined fruit. Since the juice is totally separated from the solids, the cap so prevalent in red winemaking does not exist, and so there is no need to punch down or pump over during fermentation (and there is no maceration step in the first place).
The next option is malolactic fermentation. In “malo,” lactic acid bacteria (which may already be present in the wine or may be added) metabolize harsh tasting malic acid in the wine and replace it with softer lactic acid. It is this process that creates the buttery taste evident in some Chardonnays.
The white wine may now be aged in oak barrels or casks, but the vast proportion of white wines see no oak. In some wines, oak flavors and aromas are accomplished by macerating oak chips or staves, or by adding liquid oak extract.
A further option now is lees aging, with or without lees stirring. Fermentation creates enzymes which break down yeast cells in a process called autolysis. Cells release flavor and texture compounds such as mannoproteins, amino acids, esters, aldehydes, ketones, and others. These compounds add creaminess, richness and body to white wines. Lees aging may go on for more than a year in some cases. Obviously, this step adds to the cost of the wine.
Because of color issues, the fining process, in which a fining agent attracts yeast cells (alive or dead) and other particles so that they can clump up and sink to the bottom of the tank, is important in white wine production. Subsequent filtration to remove bacterial and superfine particles is another option. The white wine is ready to be bottled, and sometimes aged in bottle.