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A colorless liquid produced by yeast in the fourth stage of enzymatic action culminating in the production of ethyl alcohol. The enzyme carboxylase forms acetaldehyde and carbon dioxide from pyruvic acid. At the next (final) stage, most of the acetaldehyde is reduced to ethyl alcohol, but a trace remains and adds to the flavor and complexity of the wine. If too much remains, it taints the wine with a strong off-taste.

Acetic Acid
All wines contain acetic acid, or vinegar, but usually the amount is quite small--from 0.03 percent to 0.06 percent--and not perceptible to smell or taste. Once table wines reach 0.07 percent or above, a sweet-sour vinegary smell and taste becomes evident. At low levels, acetic acid can enhance the character of a wine, but at higher levels (over 0.1 percent), it can become the dominant flavor and is considered a major flaw. A related substance, ethyl acetate, contributes a nail polish-like smell.

A group of bacteria that uses oxygen to convert wine to vinegar (turning ethanol into acetic acid) through an aerobic fermentation.

A compound present in all grapes and an essential component of wine that preserves it, enlivens and shapes its flavors and helps prolong its aftertaste. There are four major kinds of acids -- tartaric, malic, lactic and citric--found in wine. Acid is identifiable by the crisp, sharp character it imparts to a wine.

A term used to describe a harsh or bitter taste or pungent smell in wine that is due to excess sulfur.

The flavor that stays in the mouth after swallowing wine. Also known as a wine's finish, this flavor can be buttery, oaky, spicy, tart, bitter, etc.

A wine described as unpleasantly harsh in taste or texture, usually due to high levels of tannin or acid.

A device placed on a fermenter (usually a carboy) for the purpose of allowing carbon dioxide to escape the vessel during the fermentation process. Since the airlock is filled with a liquid (commonly water, but you could use glycerin too), it works like a check valve; CO2 can escape, but O2 can't get in and oxidize your wine.

Ethyl alcohol, a chemical compound formed by the action of natural or added yeast on the sugar content of grapes during fermentation.

Refers to a wine's clarity, not color.

The slight "dry tongue" feeling that tannin gives a wine, creating a dry sensation on the tongue and palate.

A well-balanced wine is a primary goal of the winemaker. Such a wine blends all of its components gracefully: the fruit, tannin, acid, and sugar. A wine's balance may only be realized after some aging.

A French term for stirring the lees (trub).

An inorganic fining or clarifying agent made from diatomaceous earth. Learn how to prepare bentonite for addition to your wine by reading Tom's article above.

The impression of weight or fullness on the palate; usually the result of a combination of glycerin, alcohol and sugar. Commonly expressed as full-bodied, medium-bodied or medium-weight, or light-bodied.

Glass bottles are the most common containers for storing wine. Glass is ideal because it does not affect the wine in any way, even during extended periods.

Bottle Sickness
A temporary condition characterized by muted or disjointed fruit flavors. It often occurs immediately after bottling or when wines (usually fragile wines) are shaken in travel. Also called bottle shock. A few days of rest is the cure.

A French term for the aroma of a wine. The bouquet is often the first indicator of a wine's quality during wine tasting. Aromas may include fruit, spice, and other smells associated with a particular grape variety, region, or condition of the wine. The bouquet of a Merlot, for example, will often contain aromas of raspberry and cassis (black currant).

Describes the process of allowing wine to have prolonged contact with air in order to reach full flavor. This is usually done through decanting a wine, but this can also be accomplished by simply uncorking a bottle and pouring wine into a glass and letting it sit for a while.

Allowing a wine to mix with the air. Aeration occurs by pouring the wine into a larger container, such as a decanter or large wineglass. Breathing can be beneficial for many red wines and also for some young white wines. Chemically, breathing enables oxygen to mix with the wine, which hastens the aging process. If a wine stands open for more than 12 hours, it will begin to turn to vinegar as the oxygen continues to work. Whether to let a wine breathe before serving depends on the wine. Contrary to popular belief, it is not always beneficial to let older wines breathe prior to drinking, as this can cause them to "turn" - or go bad - before dinner is over.

A clear and bright - as opposed to cloudy - appearance in wine.

The rubber stopper placed in the neck of the carboy or demijohn that holds the airlock in place with an airtight seal.

The stem of a shoot on a grapevine that has developed bark.

The solid mass of grape skins, stems, and pips (seeds) that floats to the top of the fermenting vessel during fermentation.

The protective metal or plastic sheath over the cork and neck of a wine bottle. The capsule keeps the cork from drying out and admitting air into the bottle.

A glass jug (most commonly 1 to 6 gallons) used as a secondary fermenter.

A storage area for wine, not necessarily underground. A cellar is the best area to keep wines for aging. Ideal conditions are darkness, controlled cool temperature, and high humidity. Bottles should be stored on their sides to keep the corks from drying out.

The process of adding sugar to grape juice that does not naturally possess enough sugar (brix) to make good wine.

That which makes a wine distinctive. A region's winemaking tradition, soils, and grape varieties combine to produce a wine's character.

The effect of continually heating the inside of a wine barrel over an open fire. It usually causes browning, or even blackening of the inside surface of the staves. A certain degree of toasting occurs as a normal result of the manufacturing process.

The process of removing cloudiness in the wine by filtration and/or fining.

The opposite of clear or brilliant. Possibly the result of sediment being stirred up during transportation.

Overly sweet, and lacking the correct amount of acidity to give the wine balance.

Cold Stabilization
A clarification technique in which a wine's temperature is lowered to 32° F, causing the tartrates and other insoluble solids to precipitate.

Corks are produced from the bark of cork trees, which are grown mainly in Spain and Portugal. Corks are airtight and have for years been the best way to seal wine bottles.

An expression meaning the wine has gone bad. Implies an unpleasant, musty, moldy smell imparted by a flawed cork. Cork can contain bacteria that will cause "off" flavors in the wine. Quality cork manufacturers bleach and process corks to minimize the chance of a bottle being "corked." Unfortunately, almost one out of twelve bottles will have some off, corky flavors. It is for this reason that alternative wine bottle closures have been tested in recent years, but the use of non-cork closures has been resisted by traditionalists. Any closure that seals the bottle airtight is a perfect one for wine. Contrary to popular belief, cork does not - or should not - let air into a wine bottle over time. It is intended to create an airtight seal.

A process for separating the sediment from a wine before drinking. Accomplished by slowly and carefully pouring the wine from its bottle into another container.

In bottle-fermented sparkling wines, a small amount of wine (usually sweet) that is added back to the bottle once the yeast sediment that collects in the neck of the bottle is removed.

Having no perceptible taste of sugar. Most wine tasters begin to perceive sugar at levels of 0.5 percent to 0.7 percent.

Characteristic description typical of wines that are too young or possibly too cold that refuse to reveal much flavor or bouquet at all; closed.

The science and study of winemaking. Also spelled oenology.

Ethyl Acetate
A sweet, vinegary smell that often accompanies acetic acid. It exists to some extent in all wines and in small doses can be a plus. When it is strong and smells like nail polish, it's a defect.

Extended Maceration
The process of letting the red grapes remain in contact with the juice for an extended amount of time after fermentation is complete (before being pressed), to more fully develop the flavor and richness of a wine.

Describes a wine that is losing color, fruit or flavor, usually as a result of age.

The process by which yeast converts sugar into alcohol and carbon dioxide; turns grape juice into wine.

The process of removing particles from wine after fermentation. Most wines unless otherwise labeled are filtered for both clarity and stability.

A technique for clarifying wine using agents such as bentonite (powdered clay), gelatin or egg whites, which combine with sediment particles and cause them to settle to the bottom, where they can be easily removed.

The key to judging a wine's quality is finish, also called aftertaste--a measure of the taste or flavors that linger in the mouth after the wine is tasted. Great wines have rich, long, complex finishes.

A general term used to describe the visible particles that float in unfinished wine.

Adding alcohol to a wine in order to make it stronger and take on a different character. This process also lessens the possibility of further fermentation, since many wine yeasts can't survive in a higher alcohol environment. Sherries, Madeira, and Ports are examples of fortified wines.

A fragrant wine is very aromatic and flowery. Common wine fragrances are floral, spice, and fruit aromas such as pineapple, blackberry, peach, apricot, and apple. The variety of the grape is primarily responsible for a wine's fruit fragrances.

A fruity wine is one in which fruit flavors dominate the aroma and taste. Often these wines are easy-drinking and light.

A common food additive that enhances body and mouth feel in wine, it also adds a bit of sweetness. A little bit goes a long way, so use it in moderation. Glycerin can be obtained from your local drug store or online at (ask for Item # 2749, 4 fluid oz).

Used to describe a wine that has small amounts of visible particles when viewed against the light. A good quality if a wine is unfined and unfiltered.

Describes a wine that smells or tastes grassy or green. Often a characteristic of wines made from Sauvignon Blanc and Sémillon grapes. Can also be found in very young wines that will change flavor as they age. Primarily a function of the grape variety, not soil or climate.

The deposits which gather at the bottom of the carboy during winemaking (also known as trub).

The viscous drips of wine that run down the side of a glass in which wine is swirled. If your wine lacks legs, you can add a small amount of glycerin (about 3 to 12 ml per liter) to enhance fullness and body.

The amount of time the sensations of taste and aroma persist after swallowing. The longer the better.

A term used to describe the body or color of a wine. A light wine is usually easy to drink and not high in alcohol. Muscadet is a light white wine. Beaujolais is an example of a light red wine.

Malolactic Fermentation
A secondary fermentation that occurs in most wines and converts malic acid into softer lactic acid and carbon dioxide, which reduces the wine's acidity. MLF can soften red wines (like Cabernet or Merlot), and adds complexity to hearty whites (such as Chardonnay).

Ready to drink.

A wine, common in medieval Europe, made by fermenting honey and water. Recently mead has enjoyed new popularity. Wine makers now make flavored mead.

Méthode Champenoise
French term for the method used to make champagne, which is fermented in the bottle. French champagnes and many other sparkling wines are produced using this traditional French technique. The monk Dom Pérignon is credited with inventing this method.

Mulled Wine
Red wine that has been mixed with sugar, lemon, and spices, usually including cinnamon, cloves, and nutmeg. Served hot.

The unfermented juice of grapes extracted by crushing or pressing; grape juice in the cask or vat before it is converted into wine.

An inert gas used by winemakers to take up headspace in a carboy or bottle. Since nitrogen is heavier than air, its presence helps displace oxygen and keep it away from your wine. This helps to prevent oxidation.

The character of a wine as determined by the olfactory sense. Also called aroma; includes bouquet.

The most popular wood for constructing barrels. Oak imparts flavors and tannin to wines during the barrel aging process; home winemakers can also accomplish this by using oak chips or powder.

Describes wine that has been exposed too long to air and taken on a brownish color, losing its freshness and perhaps beginning to smell and taste like Sherry or old apples. Oxidized wines are also called maderized or sherrified.

The time when a wine tastes its best--very subjective.

Pectin Haze
An undesirable gelatin-like haze in wine caused by the presence of the pectin molecule, which is usually associated with boiling or mashing of fruit to extract flavor or color. You can prevent a pectin haze by adding pectic enzyme to the must 12 hours prior to adding yeast.

A chemical measurement of acidity or alkalinity; the higher the pH the weaker the acid. Used by some wineries as a measurement of ripeness in relation to acidity. Low pH wines taste tart and crisp; higher pH wines are more susceptible to bacterial growth. A range of 3.0 to 3.4 is desirable for white wines, while 3.3 to 3.6 is best for reds.

The practice of moving wine by hose from one container to another, leaving sediment behind. For aeration or clarification.

Having the taste of raisins from ultra-ripe or overripe grapes. Can be pleasant in small doses in some wines.

A term used to describe the method of adding water to active dry wine yeast before pitching. Rehydrating wine yeast increases the yeast's chances for survival, because the structure of the cellular walls returns to normal during water uptake.

The technique of gradually inverting champagne bottles at the end of the bottle ferment. At the same time as the inversion is increased, the bottle is twisted so that the yeast falls to the neck of the bottle; from there it can be removed by disgorgement.

Residual Sugar
Unfermented grape sugar in a finished wine.

A French term which describes a dry wine.

A mechanical device that applies a tin or polylaminate capsule on a wine bottle. A series of "fingers" with Teflon wheels flatten and anchor the foil to the neck of the bottle using a spinning motion, hence its name. As a result, the one-piece tin capsule is precisely spun down onto the neck without wrinkling.

Stuck Fermentation
An undesirable condition where fermentation fails to begin, or has stopped before all the sugar has been converted to alcohol and CO2.

Sweet Reserve
A sample of the original juice from which a wine is made. It is generally used to sweeten the finished wine after fermenting to dryness and the wine is stabilized. The sweet reserve is usually refrigerated or frozen until needed. Some advantages of using a sweet reserve is that it adds sweetness, fresh flavor, and natural aroma to the wine. It may also improve the color of the finished wine.

A component of wine - found mostly in red wines - derived primarily from grape skins, seeds and stems, but also from oak barrels. Tannin acts as a natural preservative that helps wine age and develop and provides astringency that is part of a balanced wine. Excessive, unbalanced tannin can taste bitter and leaves the same drying or puckering sensation in the mouth as very strong tea.

Tartaric acid
The principal acid in wine.

Harmless crystals of potassium bitartrate that may form in cask or bottle (often on the cork) from the tartaric acid naturally present in wine.

Tawny Port
Like Ruby Port, Tawny Port is a blended wine, but one that is aged for a minimum of four years in wood casks and is lighter. It is called "tawny" because as oxidation occurs, the original ruby-red color changes into a reddish brown.

Titratable Acidity (TA)
Sometimes called total acidity; the total amount of acids in a wine or must that is measured by titration of the wine or juice with a base such as sodium hydroxide. The amount of acid (expressed in grams of acid per liter of wine) will tell you roughly how acidic the wine will feel in your mouth. Knowing this information will allow you to make any needed adjustments.

Top Up
To add liquid back to a wine to minimize dead air space in the container (i.e. a carboy). Topping up is usually done after racking, to replace the wine that could not be drawn off due to sediment. Examples of liquids used to "top up" are finished wine of the same type, grape juice, sweetened or plain water. Topping up prevents problems such as oxidation of wine (wine turning to vinegar).

The deposits which gather at the bottom of the carboy during winemaking (also known as lees).

The airspace in a carboy found between the top level of wine and the bottom of the bung (rubber stopper).

A term used to describe the variety of grapes a wine has been made from.

The science or study of grape production for wine and the making of wine.

The conversion of a fruit juice or other sweet solution into alcohol by fermentation. The term is sometimes used loosely, to include every step of winemaking from getting the fruit to fermentation and beyond.

The year a wine was made. By contrast, a nonvintage wine is one made from a blend of different years.

Micro-organisms that produce the enzymes which convert sugar to alcohol. Necessary for the fermentation of grape juice into wine.