June 23, 2007

Yeast

Yeasts are fungi and are essential to winemaking. Through their anaerobic metabolism, yeasts convert grape sugars to ethanol and carbon dioxide. Yeasts are generally divided into two main groups: those naturally present in the vineyard and those manufactured in a laboratory by an oenologist. While manufactured yeasts are used in many wines worldwide there is a growing interest in wines made with natural, or indigenous, yeasts among other natural winemaking practices.

Many producers believe that wines made using indigenous yeasts bear the stamp of the vineyard, or are a more transparent lens into terroir. There are, however, two major pragmatic drawbacks that stem from the lack of control of using natural yeasts: fermentation predictability and unwanted bacteria. If fermentation does not begin rapidly enough, unwanted and harmful bacteria multiply at an undesirable rate.

Some producers using natural yeasts gain more control over the fermentation process by making a levain. Others prefer to use a small amount of manufactured yeast to jumpstart fermentation by natural yeasts.

A Beaujolais negociant and early advocate of natural yeasts, Jules Chauvet, is credited with discovering that wines made with indigenous yeasts displayed more aromatic complexity. Some of his disciples in Beaujolais were known as “the microscope group” because they used microscopes to track bacteria in their wines made without manufactured yeasts and sulphur.

A vineyard typically has a multitude of yeasts. The high number of different yeasts is believed to contribute to a greater aromatic complexity in a wine. Many wine makers spread both lees and pomace around the vineyards in the belief that greater numbers of yeast strains will result.

Wild yeasts are easily killed off by sulphur. They are also sensitive to high alcohol levels. Most wild yeasts are killed off once a wine reaches 5% alcohol. After the wine reaches 5%, the fermentation is continued almost exclusively by saccaromyces cerevisiae yeasts naturally occurring in the environment, including on the grapes and winery equipment.

Unlike indigenous yeasts, which often act more slowly and are less predictable, manufactured yeasts have very specific characteristics, including the temperature at which fermentation begins, fermentation rates and often even the flavor profiles of the finished wine.

Posted by Christy Kohser at 3:35 PM | TrackBack

Frost Protection

A vine in winter is dormant and can withstand temperatures down to -18˚ F. Some growers half-bury, or earth-up, their vines in the Fall as protection in case winter temperatures get even colder.

More common than freezing winter temperatures harming vines (and the development of grapes) is spring frost that can threaten new green shoots. This was a devastating but common occurrence in Burgundy’s Chablis region in the first half of the 20th century.

Many growers once used a now obsolete method of frost protection called smudge pots, which were metal fuel burning canisters which were kept smoldering to increase the vineyard temperature. Many viticulturists have also experimented with devices such as large fans, but none have proven to be very effective.

Today, the most common method practiced is using a sprinkler system to encourage ice to form on the young shoots. The sprinkler water warms the ground and the vines. This warming helps the vines to minimize tissue damage as they freeze, thus protecting and insulating them from frost.

Posted by Christy Kohser at 3:32 PM | TrackBack

Clarification

The removal of suspected solids from a wine including naturally occurring yeasts and tartrates, as well as grape skins, dirt, pips (seeds) and other solids which may impart bitter flavors to a wine.

There are a number of procedures that can be employed. The simplest is through a settling process. The wine is pumped into a settling tank at a cold temperature and over time the particles sink to the bottom of the tank.

Wine may also be clarified through filtration. A machine called a rotary drum vacuum filter is specially designed to handle the large amount of solids, such as lees, generated during the winemaking process.

There are also many proponents of using a centrifuge to clarify wine mainly because it is by far the fastest method. However, detractors of this technique claim that the process strips wine of its flavor, character and sense of terroir.

Posted by Christy Kohser at 3:12 PM | TrackBack

June 11, 2007

Ex-Cellars

A descriptor that means that a wine came directly from the cellar (not a broker, store, or private collection).

This is important because wine is sensitive to heat, light, vibration, and temperature change, many of which can happen during transport. The best way to avoid these juice-damaging factors is to only move the wine twice � directly from the cellar to the seller, and again from the seller to your door.

Storing wines in a winemaker's perfect subterranean cellar until purchase keeps the aging process slow and even and results in a �fresher� sense on the palate. While you may not be able to immediately tell if it is �Ex-Cellars� by tasting, you certainly can if it�s not!

Posted by Tom Stephenson at 11:23 PM | TrackBack