From Grape to Table: The Chemistries of Wine III
Fine Arts
Of Aging
and Bottling

Helen Gillespie

[Nota: La parte 2, discute las múltiples facetas del proceso de fermentación en la elaboración de vinos]

Between the fermentation process and the bottling of wine, aging (or "cellar maturation") occurs in barrels or tanks, or in bottles, or both. For a premium wine, aging can take from eighteen months to a decade or more; for a low-cost wine, the process may be skipped entirely.

During aging, the particles in suspension gradually settle on the bottom of the container. The wines are therefore "racked" (see photo above) monthly or quarterly, depending on the winery, and the sediment removed. The final process is the assemblage of the various barrels or tanks into the wine blend. There may be up to two more years of bottle aging before the wine is released. Wine aged in a bottle is monitored in the same way as wine aged in a barrel.

John Kelly, technical director at Vinquiry (Healdsburg, CA), a specialty contract lab that offers research laboratory facilities to the industry, stresses that many of the decisions a winemaker makes are business decisions. "For instance, Chardormay for early consumption will be price-pointed at a certain level," he explains. The winemaker won't use expensive fruits and might use mechanical manipulation to move the product through the various processes quickly. As soon as the wine is through fermentation, it will be filtered and bottled and out the door. A Chardonnay destined for the low end of the market may be harvested in September and shipped the following January. This is winemaking by formula. Most of the wines we test are ultrapremium, which is more of a craft wine."

Jac Jacobs, winemaker for Topolos at Russian River Vineyards (Forestville, CA), relates aging directly to flavor. The time the wine is allowed to age is determined by the flavor. When the flavor reaches what we're seeking, the aging process is complete." Kent Kantz, winemaking lab manager at Beringer Wine Estates (St. Helena, CA), adds, 'We frequently taste wines during aging and also do analyses. Thus, winemakers can assess the analytical results along with their tasting evaluations" (see photo above) - .

Under natural storage conditions, as wines age, the natural acidity releases volatile compounds from the precursors, thereby accounting for flavor. Glycoside precursors, for example, provide substantial flavor to white wines. Mild thermal processing can induce desirable flavor changes by accelerating the release of flavor from the precursors. Although thermal processing has other advantages (e.g., inactivation of unwanted microorganisms and spoilage enzymes), most vintners prefer to let wines age naturally.


The Beringer vintner uses an atomic absorption (AA) spectrometer to measure potassium while the wine is aging. Kantz explains, "Grapes take up potassium from soils as they ripen, and potassium is therefore an important cation in wine. Potassium exchange for hydrogen ions affects pH in grapes, and the potassium level in wine also affects the tendency of potassium bitartrate to precipitate. Thus, by measuring potassium, we can get some insight into how much potassium bitartrate will precipitate during aging."

At Topolos, the emphasis is on acetic acid levels. "It is a benchmark that enables you to see a voluntary metabolite go up long before you can taste it," Jacobs says. "If the smell changes, it can indicate that the wine has a hydrogen sulfide problem. The quickest solution is to rack and aerate the wine, but that is not a permanent fix. We'll use Vinquiry for testing in this type of case."

Before the final bottling, wine may be filtered or undergo "fining" to be clarified and stabilized as part of the finishing process. Filtering removes bacterial sludge. Unfiltered wine may be the darling of wine critics, but it also is more sensitive and susceptible to spoilage. Heat and cold stabilization are used to remove unstable proteins and tartrates, respectively. For instance, during cold stabilization, the sample is frozen and then closely monitored as it thaws. 'We're looking for crystals or tartrates," explains Jacobs. "Tartrates, which occur mostly in white wines, are undesirable because they affect the stability of the wine. Because the wines sit in refrigeration a lot, we want to ensure that the character doesn't change over time. We prefer not to filter the wine whenever possible."

The industry is shifting to less and less filtering of wines," Kelly observes. "But this requires a corresponding culturing and monitoring of the wines prior to bottling to evaluate microbial status for any spoilage organisms and sediments, and focus on finishing operations." Vinquiry provides filtration analysis to determine the filterability of wine, to minimize manpower, and to optimize the filter media. The company also offers different fining trials and proteins to clarify the wine and modify the mouth feel.

Fining also clears the wine of any remaining particles before bottling, but the process is a bit more complicated than filtering. It may be as simple as the use of beaten egg whites, or as complex as the introduction of fining agents such as enological gelatins. These gelatins are made of protein and polypeptidic fractions manufactured through the hydrolysis of collagen or fibrous proteins in biological tissues. Gelatin is most commonly used just before bottling, and its chemical interaction with the wine adjusts the level of tannin and modifies flavors, aromas, bitterness, and astringency. The enologic gelatin bonds with certain protein chains to coagulate and filter out sediments and other wine components. However, as with yeasts, each fining gelatin works somewhat differently. The more it is used to soften the wine, the more tannins and color tend to be removed.


Once the wine has been aged, it is blended and bottled. Unlike other beverage bottling processes, wine bottling is more than a mechanical operation. 'Me quality of the cork and the color and shape of the bottle are of utmost importance at this stage, because these factors can greatly affect the wine. Dark glass acts as a light filter and protects wine from ultraviolet and infrared rays. Bottles with narrow necks and deep bodies naturally hold back the sediment of an unfiltered wine on pouring.The cork, however, is the main focus at this stage, because it must provide a perfect seal without tainting the flavor of the wine. Wineries invest considerable research in analyzing and purchasing only the highest quality cork. "Cork is a big issue, mainly because of cork taint," Kelly notes. "We look for mold, lignum, and anisole or chlorine. We're looking for chemical reactions at levels less than a drop of water in a swimming pool, but poor quality cork can impart a musty, sticky aroma to wine."

"During bottling," Kelly continues, "we check the sugar level and ensure that there is no yeast in the finished product We also check the alcohol level and provide an alcohol certificate based upon our findings." All wine must be tested before bottling, and the final results must be provided to the Bureau of Alcohol, Tobacco, and Firearms (BATF) by a BATF-certified lab (Vinquiry is a BATF-certified lab, as is Beringer's lab). Some of this information must be

Research has shown that monoterpenes in the grape contribute to the flowery, fruity flavor characters that the wines of Muscat varieties often exhibit. Varieties such as Sauvignon Blanc and Cabernet Sauvignon exhibit vegetal characteristics because of a compound called pyrazene. However, for most nonfloral varieties (i.e., those not of the Muscat family, such as Chardonnay), the grape-derived volatiles important to wine flavor are basically unknown.

Given the gaps in knowledge about wine, it is hardly surprising that the science of winemaking focuses on the chemistries that affect fermentation. 'Me steps that are taken during this key stage are all geared toward delivering an end product that meets with consumer approval. However, the efforts of the winemaker and the wine lab may well be underappreciated because, regardless of the chemistry involved, personal tastes differ. Nevertheless, the experts offer the following tips to ensure that the consumer gets the most satisfaction from the end product.

Analysis of wine involves key steps that seek to determine four sensations: visual, olfactory, degustatory, and tactile.

Visual. When sampling a wine, first observe the color and determine whether the wine is clear or cloudy. Clarity and a visually stimulating color are desirable.

Olfactory. Next, swirl the wine and take a sniff. Swirling the wine releases its aromas. Although people can taste only four flavors, most people can identify some 5,000-8,000 odors. Aromas indicate whether the wine is free of flaws, such as excessive sulfur or cork taint, and how flavorful the wine is.1be flavor quality of a wine is judged on a subjective determination of the aromas' desirability, complexity, and depth.

Degustatory. Now, taste the sweet, salty, sour, and bitter flavors of the wine. Too much alcohol provides a burning sensation at the back of the palate. Tannin imparts a dry, oaky, rough flavor and feeling (similar to tea) that dries up the saliva. Even though acid is a bitter flavor, it enhances wine by helping to develop the natural fruitiness and crispiness in the flavor. If the wine is flat, it doesn't have enough acid. A fruity wine will have 1- to 5-percent residual sugar. Despite fermentation, all wines have a touch of sugar, but the fruitiness-rather than the sugars should be most apparent.

Finally, feel the viscosity of the wine on the tongue, and test the body. Savor the tactile sensation that the wine provides.

The winemaker's goal is to provide a pleasurable combination of the four sensations and a balance of the four flavors. Achieving this balance is the point of all the chemical monitoring and analysis that goes into wine production.

As Jacobs points out 'When it comes down to it the consumer doesn't care about the chemistries, just what the wine tastes like." No matter how well the winemaker or wine lab manager performs the analytical tasks associated with the wine's chemistry, the consumer has the final say on the result of months-even years-of work. Perhaps this reason alone is why winemaking is as much an art as a science.

HELEN GILLESPIE is an industry analyst, editorlpublisher of the LIMS/Letter, and Webmaster of the LIMSource. Can be reached at RO. Box 935, Kenwood, CA 95452. Tel.- 707-833-6885; Fax.- 707-833-6865,- E-mail: Webmaster@LIMSourcexom; Web:


The Bureau of Alcohol, Tobacco, and Firearms (BATF) regulates winery operations. The emphasis of the bureau is to collect taxes based on the alcoholic content of the wine and to ensure accurate labeling. Wine reported as less than 14 percent alcohol is taxed at $1.07 per gallon. Between 14 and 21 percent alcohol, wine is taxed at $1.57 per gallon. From 21 to 24 percent, the tax is $3.15 per gallon. In addition to asking for lab samples and test results to confirm the contents of any given wine, the BATF buys wine off the shelf and tests those bottles.

BATF-certified labs have a quality program in place to ensure the accuracy of the various measurements and compliance with paperwork requirements. Small wineries such as Topolos rely on BATF-certified labs to perform the final analyses. 'When the alcohol readings get close to the desired level, we start sending samples to Vinquiry," says Jacobs. "All our sugar and alcohol tests are done by Vinquiry." The information from these tests then must be transferred to the wine labels -also monitored by the BATF-which must be scrupulously correct. The levels of the various components in wines monitored by the BATF are based on a set of Required Analitycal Tests for Wines.

All laboratories keep records to show that the wine contents match the labels. "For instance," Jacobs explains, "To say Pagani Ranch, 95 percent of the grapes must be from that site. To say Zinfandel, 75 percent of the grapes must be Zinfandel. Alcohol readings can be ±1.5 percent of the amount specified on the label, as long as they correspond to the lab notes. If a wine is over 14 percent alcohol, taxes on the wine are higher and the winery would need to charge more for the wine to cover the costs. The industry prefers to keep alcohol below 14 percent as a result"

Topolos, like most wineries, uses grapes from several vineyards. Wine from grapes grown exclusively on the Pagani Ranch in the Sonoma Valley can state so on the label. A wine with a label that reads "Sonoma County" can contain grapes grown anywhere in Sonoma County. A blended wine that uses grapes from a variety of California locations can state that it is a California Zinfandel, meaning that the grapes must have been grown in California. Needless to say, the cachet of grapes from the Sonoma and Napa valleys is greatest, and these wines tend to command a higher price, so wineries strive to develop vineyard-specific wines whenever possible.