Vintner's Corner

Vol. 14, No. 3 May - June, 1999


Bruce W. Zoecklein

Department of Food Science and Technology

VPI & SU - 0418

Blacksburg, VA 24061, E-mail:

Table of Contents

I. Aroma and Flavor Integration Considerations 1

II. Micro oxygenation 3


I. Aroma and Flavor Integration Considerations

The following on oak and wine aroma/flavor integration is a preview of some of the many practical issues which will be discussed at the International Symposium: Oak From Forest to Glass, St. Louis, Missouri, July 14-17, 1999. (Contact my office for registration information or see last issue.)

Quality components, in large measure, are the result of fruit characteristics. What is sought in Chardonnay grapes is desirable grape aromas/flavors and intensity. Overlaid on the basic quality from the grape is the mark of the winemaker. In barrel fermented wines such as Chardonnay we are looking for a series of wood notes to support aromatic panoply of the wine. The most complex and, therefore, the most attractive flavors imply an intermediate stage of all the flavor formation and degradation. Excessive aroma/flavor change stemming from too much oakiness, aggressive tannins, etc., overbalances the impression of flavors, resulting in a less complex, one dimensional product. Processing considerations must reflect the importance of aroma and flavor balance and integration. A skillful winemaker, therefore, is one who can adjust production variables in such a way so as to emphasize one or more of the aromas, flavors and textures to produce the well-balanced, integrated product. Wine styles differ because of the tremendous number of variables that come into play in grape growing and in the winemaking process. Fruit structure and flavor should dictate winemaking techniques. The most important element of the winemaker's decisions is the degree or amount of varietal intensity.

By fermenting and / or storing in wood, winemakers hope to achieve color stability, softer tannins, added complexity through oxygen exchange and oak aroma/ flavor. Wood tannins, hemi-cellulose and lignins produce a host of volatile phenols that are extracted from the wood either before or following fermentation. Some of the aroma notes that are derived from phenols are listed in Table 1. Barrels produced from different sources have different structures and textures, and these influence the aromas and flavors imparted to the wine. The principal barrel production factors influencing these aroma descriptions are wood grain, age / size, method of drying or seasoning, location of seasoning, cooperage techniques, stave width, and degree of toasting.



COMPONENTS FROM OAKPolysaccharides*, cellulose, tannin*,

hemicellulose*, lignin*








* Contribute to aromas

The sensory response to different wood sources depends on a host of factors. Additionally, the specific influence of barrel production practices on the aroma and flavor notes imparted to wine is difficult to categorize because each vintage is different. As a result, we are not always sure if the influence is from the barrel parameter or the vintage or both. Each of these factors influences the production of volatile components. How long the wine has been in the barrel when it is evaluated also makes a large difference. This is the oak and Chardonnay integration factor. Frequently after 90-100 days in the barrel there is a loss of distinctive aromas like burnt, toast, and charred, and a decline in the ability to identify oak origin.

Where the wood is seasoned appears to be an important sensory factor, and one that has been some-what overlooked. Exposure has a cleansing effect as it removes the most easily extractable tannins and other polyphenols which are also the most bitter. Exposure to the elements promotes the growth of microorganisms, the enzymes of which help to digest hemi-cellulose and lignins, thus aiding the aromatic preparation of the wood.

Toasting causes a redistribution of polyphenols and, more specifically, the production of volatile phenols, depending upon the intensity and duration of heat. As heat is increased, there are a number of changes that occur in the wood. Most importantly, barrel toasting can cause changes in the sensory

response of wines. It is interesting to note that aromas like smokey, burnt, and charred are not always the result of heavy barrel toasting. Toasting may be important because it leads to a breakdown of polysaccharides and polyphenols, thus potentially adding to the complexity. Too much heating, however, causes a reduction in the potential aroma diversity. The specific influence of toasting on the sensory aspects of wine have been difficult to define due to vintage variations and the heat and duration of toasting, as well as other barrel production features.





Some barrel fermentation considerations influencing aroma and flavor are listed in Table 2. The effect of most of these factors is understood. Temperature control is of obvious importance. Generally we want 16-18OC for maximum aroma and finesse. In years with particularly assertive fruit characteristics some winemakers prefer warmer fermentation temperatures of about 23OC. Temperature may also be an important consideration regarding malolactic fermentation. It is desirable to avoid cold barrel fermentations, particularly in the presence of SO2, because bitterness can result.

Lees contact is frequently a production component in Burgundian style Chardonnay. Lees contact contributes to the complexity of the wine by the integration of yeast characteristics with fruit and wood flavors. Lees management is, therefore, certainly an important aroma and flavor consideration. Lees nourish the wine during aging, imparting aromas and structure by filling out the body and adding depth, length and complexity. Table 3 shows some important considerations regarding lees management.





During lees contact the composition of the wine changes as the yeast commence enzymatic hydrolysis of their intracellular constituents. One important feature is the process of proteolysis, whereby proteins are hydrolyzed to amino acids and peptides. These compounds then pass through the cell wall resulting in an increase in the nitrogen content of the wine. It is known that amino acids can act as flavor precursors, possibly enhancing wine complexity and quality.

Lees stirring and the frequency of stirring is important, both as a practical and stylistic consideration. Stirring is an oxidative process which increases the acetaldehyde content and which may increase the acetic acid concentration. Stirring also changes the sensory balance between fruit, yeast and wood by enhancing the yeast component, reducing the fruit, and, to a lesser degree, the wood component. Additionally, stirring may have the effect of enhancing secondary chemical reactions, possibly as the result of oxygen pick-up. Stuckey et al. (1991) demonstrated increases in both the total amino acid content and wine sensory score in wines stored for five months without stirring. The non-stirred wine was perceived to have greater fruit intensity.

MLF reduces the harshness of new oak and aids in the development of complex and mature flavors. Traditionally, stirring is continued until MLF is complete. After that, the lees are said to become more dense, so as to aid in clarification.

During barrel aging what we are looking for is slow, well-managed, and controlled oxygenation. Lees allow for this oxygenation and they aid in the prevention of oxidation. Traditionally in Burgundy, wines are racked off the lees in March, usually the time when MLF is completed. Frequently this is an aerobic racking off the heavy lees then back into wood on light lees followed by an SO2 addition. Leaving the wine on the light lees helps to nourish the wine. The addition of SO2 helps to protect the wine from oxidation. A subsequent racking often occurs in early July and is in the absence of air. Timing of SO2 additions and the quantity of SO2 added are important stylistic considerations. Early use of SO2 increases the number of components that bind subsequent additions of SO2. The addition of too much SO2 counters the wood flavors and limits oxidation reactions, while too little SO2 may allow the wine to become tired and overaged. Production considerations such as the method of barrel storage and time of bottling are factors influencing SO2 levels. Barrel topping is an aerobic process that can result in excessive oxidation. Additionally, wines that spend a second winter in the cellar tend to lose their aroma unless the wine is particularly rich.

If fruit such as strawberries or apples are made into wines, the public expects them to have the flavor of fresh fruit. Fortunately no such expectations apply to grape wines, partly because few consumers have any preconceived notions regarding wine grape flavors. This allows for a broad degree of stylistic freedom. What the public does expect in a barrel fermented Chardonnay, however, is a well-balanced wine, one that possesses a whole symphony of integrated flavors and aromas. To produce such a wine requires an understanding of the grape and how each processing variable influences the balance of fruit, wood, bacterial and yeast aroma and flavor notes.

These and other topics will be discussed at the international Symposium - Oak from Forest to Glass. See you in St. Louis!

II. Micro Oxygenation

Oxygen contact with must and wine is a concern throughout the winemaking process. As discussed in the last edition, oxygen contact during bottling can be quite detrimental and should be monitored. In some instances, such as juice processing and during barrel aging, controlled exposure to oxygen may play an important and beneficial role in wine quality.

Controlled aeration enhances phenol polymerization including both color stability and suppleness in red wines. The binding of pigments with tannins to form stable color complexes involves both oxidation and nonoxidation mechanisms. It is believed that acetaldehyde produced by coupled oxidation of ethanol forms a bridge between tannins and pigments. Sulfur dioxide can inhibit or retard the formation of tannin-pigment complexes by binding free acetaldehyde. For this reason, many winemakers splash rack their red wines perhaps four times during the wines' first year.

We know that too much oxygen contact produces excessive acetaldehyde, over-oxidizing the wine. Many are now measuring the concentration of molecular oxygen being dissolved in wine as a result of splash racking. Research continues on systems which deliver small concentrations of air (02) into wine to maximize red wine suppleness and color stability.