By Ed McCarthy, Mary Ewing-Mulligan

A good wine is, above all, a wine that you like enough to drink, because the whole purpose of a wine is to give pleasure to those who drink it. After that, how good a wine is depends on how it measures up to a set of (more or less) agreed-upon standards of performance established by experienced, trained experts.

These standards involve mysterious concepts like balance, length, depth, complexity, finish, and trueness to type (typicity in Winespeak). None of these concepts is objectively measurable, by the way.

Balance

The three words sweetness, acidity, and tannin represent three of the major components (parts) of wine. The fourth is alcohol. Besides being one of the reasons you often want to drink a glass of wine in the first place, alcohol is an important player in wine quality.

Balance is the relationship of these four components to one another. A wine is balanced when nothing sticks out, such as harsh tannin or too much sweetness, as you taste the wine. Most wines are balanced to most people.

But if you have any pet peeves about food — if you really hate anything tart, for example, or if you never eat sweets — you might perceive some wines to be unbalanced. If you perceive them to be unbalanced, then they are unbalanced for you. (Professional tasters know their own idiosyncrasies and adjust for them when they judge wine.)

Tannin and acidity are hardening elements in a wine (they make a wine taste firmer and less giving in the mouth), while alcohol and sugar (if any) are softening elements. The balance of a wine is the interrelationship of the hard and the soft aspects of a wine — and a key indicator of quality.

To experience the principle of taste-balance firsthand, try this: Make a very strong cup of black tea and chill it. When you sip it, the cold tea will taste bitter, because it’s very tannic. Now add lemon juice; the tea will taste astringent (constricting the pores in your mouth), because the acid of the lemon and the tannin of the tea are accentuating each other. Now add a lot of sugar to the tea.

The sweetness should counterbalance the acid-tannin impact, and the tea will taste softer and more agreeable than it did before.

Length

Length describes a wine that gives an impression of going all the way on the palate — you can taste it across the full length of your tongue — rather than stopping short halfway through your tasting of it. Many wines today are very upfront on the palate — they make a big impression as soon as you taste them, but they don’t go the distance in your mouth. In other words, they’re short. Generally, high alcohol or excess tannin is to blame. Long length is a sure sign of high quality.

Depth

Depth is another subjective, unmeasurable attribute of a high-quality wine. A wine has depth when it seems to have a dimension of verticality — that is, it doesn’t taste flat and one-dimensional in your mouth. A “flat” wine can never be great.

Complexity

Nothing is wrong with a simple, straightforward wine, especially if you enjoy it. But a wine that keeps revealing different things about itself, always showing you a new flavor or impression — a wine that has complexity — is usually considered better quality. Some experts use the term complexity specifically to indicate that a wine has a multiplicity of aromas and flavors, while others use it in a more holistic (but less precise) sense, to refer to the total impression a wine gives you.

Finish

The impression a wine leaves in the back of your mouth and in your throat after you swallow it is its finish or aftertaste. In a good wine, you can still perceive the wine’s flavors, such as fruitiness or spiciness, at that point. Some wines may finish hot, because of high alcohol, or bitter, because of tannin — both shortcomings. Or a wine may have nothing much at all to say for itself after you swallow, which tells you that it is probably not a great wine.

Typicity

In order to judge whether a wine is true to its type, you have to know how that type of wine is supposed to taste. So you have to know the textbook characteristics of wines made from the major grape varieties and wines of the world’s classic wine regions. (For example, the Cabernet Sauvignon grape typically has an aroma and flavor of black currants, and the French white wine called Pouilly-Fumé typically has a slight gunflint aroma.)