White wine production technology
Peter Bell

Much of what you have read in the section on red winemaking will also pertain to white winemaking, so this section will be a lot shorter.

With white grape varieties, varietal flavor can be the most important organoleptic aspect of the wine. A good Riesling, Gewurztraminer or Muscat, for example, show grape-derived aromas above all else. Thus it is very important indeed to match grape variety with region. Harvest Parameters

The same considerations as with red grapes apply. With certain varieties, Riesling and Vignoles for example, there is a much larger harvest window - as much as two months in some cases. White grapes are more tolerant of cool climates than reds, though they can easily suffer from too much acid at harvest.

On another note, many warm-climate Chardonnays have too much sugar, and thus potential alcohol, at ripeness. If they were to be picked at lower sugars they would have inadequate varietal flavor - an example of sugar accumulation and flavor development being out of 'sync'.

With some grape varieties, acids can drop drastically in grapes as they approach ripeness. Gewurztraminer, especially, suffers from this problem: fully ripe grapes can have a pH of 3.6 and a T.A. of 4 g/L. Some winemakers even choose to pick the grapes while the acid is still at reasonable levels (but before flavors develop). Others simply choose to make early additions of acid, often at the crusher, so that they have the benefit of maximal varietal flavor.

With regard to disease pressure, white grapes can often tolerate a greater infection with out quality being compromised. In fact, an infection of 'dry' botrytis can make for a better wine with many varieties.

Many white wine styles require very low extraction of phenolic compounds if they are to have the desired delicacy of flavor. To this end, many winemakers go to great extremes to pick and transport white grapes very gently. Also, super-protective handling (i.e., almost total exclusion of oxygen),such as is practiced in parts of Australia, begins at the moment that the grapes are picked.

This technique - loading uncrushed, whole grape clusters directly into the press - is imperative with high quality sparkling wine production. It is also a logical, if time-consuming, practice in some cases with white table wines. Whole-bunch pressing leads to a juice with the lowest possible phenolics, very low solids, and fine, delicate flavors. Some hot-climate Chardonnays and Rieslings are made this way.

Chilling of must (freshly crushed grapes) is common with white grapes produced in warm regions, even though it is extremely costly.

Many varieties, notably Gewurztraminer, are given a number of hours of skin contact after crushing and before pressing. This is a way of extracting more flavors from the grapes - the aromatic compounds known as monoterpenes found in some varieties are concentrated in and just under the skin. Skin contact requires specially-designed equipment. Risks associated with skin contacting range from excessive phenolic extraction, with an attendant increase in astringency and premature aging, to increases in the pH of the juice, to the extraction of flavors that aren't that nice after all.

Winemakers customarily make additions of specially-prepared pectolytic enzymes to white musts in an effort to increase the yield of clear juice and hasten the settling process. Although all crushing and pressing operations are in truth inherently oxidative, there is some virtue in employing techniques which exclude as much air as possible; and in other cases deliberately oxidizing the juice.

Oxidative handling involves making low or no additions of SO₂ to the must, and making no attempt to protect the juice from air. This allows polyphenol oxidase enzymes to oxidize grape phenols, which eliminates any browning precursors. Primary fruit flavors are also reduced in intensity. Wines treated this way tend to have more delicacy and a greater capacity to age well. Malolactic fermentation is also made easier, as there is little or no SO₂ .

Protective handling involves making use of low temperatures, inert gases, and antioxidants such as SO₂ and ascorbic acid. White grape juices treated this way retain their vibrant green color, and more of their primary fruit flavors end up in the finished wine.

As a generalization, the most finely flavored white wines come from grapes that were pressed over an extended period of time - up to two hours in some cases. (Contrast this with the half hour or so taken to press off red wines.) The combination of very low pressures and long draining periods give a juice with great delicacy.

This regimen is not always feasible at harvest time, when throughput is a key operative. High quality wines can also be made with faster press cycles, as long as the winemaker is alert to the potential problems involved.

Separating different fractions of juice so that they can receive different treatments is a practice that originated in Champagne. Recently more and more winemakers are employing this technique with high quality still wines. The separation of high-pressure juice allows the winemaker to fine it at a higher level, or use it in a lower-priced blend.

Juice fractioning is a powerful tool for influencing pH, T.A., phenolics, mouthfeel, and fruit flavors in white wines.

The standard way to remove bits of solid matter from a white grape juice prior to fermentation is by settling. A settling period of about 24 hours is usually sufficient to clarify a juice. Although settling is normally done at cold temperatures, it should be noted that cold juices actually settle more slowly than warm juices.

Large wineries often clarify juices with a centrifuge or by filtration with diatomaceous earth.

Manipulation of solids content in juices can be an important stylistic tool. The French, especially, feel that the most complex wines come from fermentation with a high percentage of grape solids: 5-10%. High-tech New World wineries sometimes clarify their juices to below 0.1% solids.

Depending on the grape variety and wine style, fermentation of whites can take place in inert vessels, in oak barrels, or in a combination of the two. Barrel fermentation, particularly with Chardonnay and Sauvignon Blanc, has been practiced in France for a very long time, but it is a relatively recent (early 1980s) technique in the New World.

Much effort is put into the search for the perfect yeast strain for a given white wine. It is not unusual for a winemaker to try out 10 or 15 different strains in a year, evaluating them for a large number of criteria, such as:

SO₂ tolerance
tendency to foam
behavior at a certain temperature
alcohol tolerance
acid metabolism
competitive (killer) factor
H2S production
CO₂ tolerance
flocculation (ability to settle)
production of desired flavor compounds
modification of mouthfeel
compatibility with ML bacteria

Fermentation temperature with white wines is generally lower than that of reds, in the range of 10-20o C. Low temperatures tend to produce wines with more fruity esters, at least when they are young; higher temperatures produce wines with greater vinosity and complexity. With most white wine fermentations temperature control is imperative, although barrel fermentations tend to be self-limiting in this regard.

Chaptalization is practiced with whites, but not as frequently as with reds.

Many white wines are left with some residual sugar, and the most common way to do this is by stopping the fermentation. This can be done by rapid chilling, or by physically removing the yeast from the wine by filtration or centrifugation. In both cases a follow-up addition of SO₂ is necessary.

By far more whites than reds suit a no-MLF regimen. While some white wines are improved by malolactic fermentation, others - especially those from aromatic grape varieties - would lose their appeal. In regions such as northern France and Switzerland, MLF is sometimes imperative as a deacidifying tool, even with aromatic varieties, in order to make the wines remotely palatable.

With Chardonnay, and to a lesser extent Sauvignon Blanc, MLF is an important tool for making a wine more complex. As with red wines, the lactic acid bacteria strain and the vessel used have a major effect on the outcome.

Most of the considerations for red wine barrel aging apply to whites. In addition, the practice of leaving a fermented wine in barrel in contact with its fermentation lees (dead yeast cells) is a common practice. Many white wines from the Loire Valley used to have on their labels the phrase, "Mis en bouteille sur lie", a somewhat oblique reference to extended lees aging.

Wines left in contact with lees, especially when the lees are periodically stirred up, develop a somewhat nutty aroma and increased creaminess or richness in the mouth. In addition, the presence of lees affects the redox potential of the wine, making it much more resistant to oxidation. Another benefit is that white wine on lees tends to pick up oak flavors less vigorously, and to integrate them into the character of the wine more readily.

White wines usually require fining with varying amounts of bentonite, in order to achieve stability with regard to heat-sensitive proteins.

A range of protein-containing fining agents are also used, such as gelatin, casein, and egg albumen. (A traditional European fining agent is cow's blood, but we won't talk about that.) These agents react with the dimeric and polymeric phenolic compounds in the wine by hydrogen bonding.

Copper sulfate, to remove hydrogen sulfide, and activated carbon, to remove off-colors and odors, also have their place in the winemaker's repertoire.

Acid and sugar adjustment are important steps for many white wines. Often very small additions of acid can make a wine taste fresher and more lively, and the addition of sugar (where legal) or 'sweet reserve' juice can improve a wine dramatically.

Just as with reds, blending can take place within or across varieties. A typical high quality Chardonnay from California might consist of a blend like this one:

40% vineyard 'A' Chardonnay
20% vineyard 'B' Chardonnay
15% vineyard 'C' Chardonnay
5% each vineyards 'D', 'E', 'F' Chardonnay
10% Semillon

Then, of the vineyard 'A' Chardonnay, there might be the following lots:

50% fully barrel fermented, French oak
25% fully barrel fermented, American oak
15% partially barrel fermented
10% stainless steel fermented

Then, of the fully barrel fermented, French oak lot, there might be the following small lots:

70% aged on lees, lees stirred every two weeks
20% racked off lees, returned to barrel
10% removed from barrel immediately after fermentation

This hypothetical blend breakdown does not even incorporate such variables as barrel age, yeast strain, malolactic fermentation regimen or SO₂ addition. So you see, there's a lot to think about and a lot to be learned in this kind of undertaking!

Cold stabilization is an optional practice but with white wines it is usually carried out. If winery owners could be assured that the wine drinking public would stop being alarmed by potassium bitartrate crystals in the bottle, cold stabilization would be practiced much less often.

Filtration of white wines is almost always carried out, in contrast to some red wines. This is because they often contain residual sugar, and because a slightly cloudy white wine looks a lot worse than a slightly cloudy red wine.

In addition to the considerations mentioned in the section on red wine bottling, there are a few things specific to whites. Some winemakers pay attention to managing dissolved CO₂ ; wines can be either improved or diminished by small amounts of this gas. In addition, winemakers (especially in Australia) add ascorbic acid at bottling to 'mop up' any oxygen that may enter the wine.

It is in some senses a shame that so many white wines hit the shelves at a young age. Many fine Rieslings, for example, get sold and drunk long before they have a chance to acquire the stunning bottle-age complexity they are capable of.