Open That Bottle
Did you open that special bottle this past Saturday? Six years ago Wall Street Journal “Tastings” columnists Dorthy J. Gaiter and John Brecher invented Open That Bottle Night, the world-wide celebration of friends, family and memories during which you finally open that bottle of wine that otherwise is too special to open.
Contrary to what you might think, more bottles of wine are opened too late rather than too early. Although we hear much about laying bottles down to age, few wines get much better after their release from the winery. Skilled winemakers release their wines ready to drink after aging them for the necessary time in their own cellars. Therefore, when the wine reaches your table it is ready to be enjoyed.
Wines do change over time due to the slow chemical reactions that occur within their bottles. For many people, these changes add complexity, new flavors, and aromas to the wine, making it more enjoyable. For others, the fruit forward or tannic style of young wines is favored.
In either case, it is better to drink up rather than wait for that special occasion. Such a strategy ensures that special wine is opened when it can be enjoyed, rather than too late when all its beauty has turned to vinegar and disappointment.
Barry P. Chaiken, Proprietor
Fermentation – Not Just Sugar to Alcohol
The process of fermentation in wine turns grape juice into an alcoholic beverage. During fermentation, yeast interact with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide (as a by-product). In winemaking, the temperature and speed of fermentation are important considerations as well as the levels of oxygen present in the must at the start of the fermentation. The risk of stuck fermentation and the development of several wine faults can also occur during this stage, which can last anywhere from 5 to 14 days for primary fermentation and potentially another 5 to 10 days for a secondary fermentation. Fermentation may be done in stainless steel tanks, which is common with many white wines like Riesling, in an open wooden vat, inside a wine barrel and inside the wine bottle itself as in the production of many sparkling wines.
The natural occurrence of fermentation means it was probably first observed long ago by humans. The earliest uses of the word “Fermentation” in relation to winemaking was in reference to the apparent “boiling” within the must that came from the anaerobic reaction of the yeast to the sugars in the grape juice and the release of carbon dioxide. The Latin fervere means, literally, to boil. In the mid-19th century, Louis Pasteur noted the connection between yeast and the process of the fermentation in which the yeast act as catalyst and mediator through a series of a reaction that convert sugar into alcohol. The discovery of the Embden-Meyerhof-Parnas pathway by Gustav Embden, Otto Fritz Meyerhof and Jakub Karol Parnas in the early 20th century contributed more to the understanding of the complex chemical processes involved in the conversion of sugar to alcohol.
In winemaking, there are distinctions made between ambient yeast which are naturally present in wine cellars, vineyards and on the grapes themselves (sometimes known as a grape’s “bloom” or “blush”) and cultured yeast which are specifically isolated and inoculated for use in winemaking. The most common genera of wild yeasts found in winemaking include Candida, Klöckera/Hanseniaspora, Metschnikowiaceae, Pichia and Zygosaccharomyces. Wild yeasts can produce high-quality, unique-flavored wines; however, they are often unpredictable and may introduce less desirable traits to the wine, and can even contribute to spoilage.
Traditional wine makers, particularly in Europe, advocate use of ambient yeast as a characteristic of the region’s terroir; nevertheless, many winemakers prefer to control fermentation with predictable cultured yeast. The cultured yeasts most commonly used in winemaking belong to the Saccharomyces cerevisiae (also known as “sugar yeast”) species. Within this species are several hundred different strains of yeast that can be used during fermentation to affect the heat or vigor of the process and enhance or suppress certain flavor characteristics of the varietal. The use of different strains of yeasts is a major contributor to the diversity of wine, even among the same grape variety.
The addition of cultured yeast normally occurs with the yeast first in a dried or “inactive” state and is reactivated in warm water or diluted grape juice prior to being added to the must. To thrive and be active in fermentation, the yeast needs access to a continuous supply of carbon, nitrogen, sulfur, phosphorus as well as access to various vitamins and minerals. These components are naturally present in the grape must but their amount may be corrected by adding nutrient packets to the wine, in order to foster a more encouraging environment for the yeast. Oxygen is needed as well, but in wine making, the risk of oxidation and the lack of alcohol production from oxygenated yeast requires the exposure of oxygen to be kept at a minimum.
Upon the introduction of active yeasts to the grape must, phosphates are attached to the sugar and the six-carbon sugar molecules begin to be split into three-carbon pieces and go through a series of rearrangement reactions. During this process, the carboxylic carbon atom is released in the form of carbon dioxide with the remaining components becoming acetaldehyde. The absence of oxygen in this anaerobic process allows the acetaldehyde to be eventually converted, by reduction, to ethanol. During the conversion of acetaldehyde, a small amount is converted, by oxidation, to acetic acid which, in excess, can contribute to the wine fault known as volatile acidity (vinegar taint). After the yeast has exhausted its life cycle, they fall to the bottom of the fermentation tank as sediment known as lees.
Other Compounds Involved
The metabolism of amino acids and breakdown of sugars by yeasts has the effect of creating other biochemical compounds that can contribute to the flavor and aroma of wine. These compounds can be considered “volatile” like aldehydes, ethyl acetate, ester, fatty acids, fusel oils, hydrogen sulfide, ketones and mercaptans) or “non-volatile” like glycerol, acetic acid and succinic acid. Yeast also has the effect during fermentation of releasing glycoside hydrolase which can hydrolyse the flavor precursors of aliphatics (a flavor component that reacts with oak), benzene derivatives, monoterpenes (responsible for floral aromas from grapes like Muscat and Traminer), norisoprenoids (responsible for some of the spice notes in Chardonnay), and phenols.
To be continued…