Your server pours a small amount of wine in your glass, you swish it around, taste it, and have an immediate sensory experience. The complexities involved in this seemingly simple process are really interesting, so let me use this column to explain.

Let’s start with a crucial physiological fact: Each of us has 10,000,000 olfactory receptors for the sense of smell, but only about one hundredth as many taste buds. Much of what we “taste” is based on aromas we detect. When tasting wine, sniff the wine and take a small amount into your mouth and swirl it around. The warmth of your mouth will release substances (esters and aldehydes) which diffuse into the nasal cavity. Keeping this in mind, it then helps to separate tasting qualities into four major categories: Fruit, Tannins, Acidity, and Sweetness.

Fruit: This is the flavor of the specific grape variety that produces the wine, which range from bland to distinctive. Most of the varietal character, or flavor, of the wine is extracted from the skins of the grapes during fermentation.

Tannins: These natural chemical compounds, antioxidants, act as preservatives and they contribute more tactile sensation than flavor to a wine. They are found in certain wood used in barrels for aging as well as in the skins, seeds, and stems of the (mostly red) grapes. Tannins can also be found in mouthwashes and teas. Some tea drinkers deliberately add milk to tea to neutralize the tannins. I don’t suggest doing that with wine, however, it does help to explain why cheese and red wine go so well together. White wines can contain tannins too. When they are vinified with prolonged skin contact or stored in oak barrels, the tannins are maximized. For many drinkers, tannins impart a tooth-coating aspect to wine and a mouth puckering astringency. Over time, the tannins tend to break down and are precipitated to the bottom of the barrel or bottle to form sediment.

Acidity: Wine that is described as “flabby, lifeless, weak, watery” etc. usually lacks acidity. On the other hand, if adjectives like “crisp” and “refreshing” are used, that usually means there’s a balance of acidity. Acidity is more important in white wines which are lacking in tannins and other flavor elements extracted from the skins.

Sweetness/Sugar: People vary tremendously in the way they perceive sweetness. Wines that are low in sugar are said to be “dry.” The average person perceives wine to be sweet when the residual sugar reaches 1.0% by weight. However some of us can detect sugar when it’s only half that amount while others, who lack sensitivity, fail to notice 2.5% sugar.

As a general rule, as grapes mature on the vine the sugar content increases and the acidity decreases. The more sugar in the grape, the easier it is to create a high alcohol content. Tartaric and malic acids occur at maximum concentrations in immature grapes. As the fruit matures and ripens on the vine, the sugar content rises to around 20% while the acids decrease from about 3% to .05%. Thus the timing of the grape harvest is critical to the final character of the wine.

There are two ways to produce a sweet wine: leave the grapes on the vine until they are overripe or exceptionally replete with sugar, or stop the fermentation before the sugar is totally converted into alcohol. Ice wines and “late harvest” wines are made by leaving the grapes on the vine until they freeze. The moisture in the grape exits through the skin and the remaining sugar is concentrated. Sauternes is a classic dessert wine, made from a combination of Semillon and Sauvignon Blanc grapes which have often been colonized by a “noble rot” which shrivels the grape and concentrates the sugar. The wines produced from such grapes are high in both alcohol and sweetness, usually with alcohol levels of 12-14% and residual sugar ranging from 5-15%.

Our subjective perception of flavor varies with the temperature of the wine and the food with which it is served. For example, chilling brings out the acidity in white wine, but reduces the tannins in red and if you pair sweet food with dry wine, you accentuate the acidity in the wine.

There is so much more to be said about the tasting of wines. If there is some interest expressed in my blog WCNY.org/starkside, I’ll go into more detail in a future column. In the meantime I hope after reading this that you have a better appreciation of the complexity of wine tasting.