Most people assume that the longer that you keep a wine, the better it will get. So probably the most commonly asked question you hear is, how long do I keep the wine before drinking? (Since its best to store wine under certain conditions, like in a cool damp underground cellar, this is known as "cellaring" wine.)
It is a misconception that you must age wine. The fact is, throughout the world, most wine is drunk "young" (that is relatively soon after it is produced, perhaps 12 to 18 months), even wines that are "better" if aged. While some wines will "mature" and become better over time, others will not and should be drunk immediately, or within a few years. Eventually all wine will "go over the hill," so even the wines meant to be kept for many, many years should be drunk before its too late.
Wines which are expected to be matured in the bottle before drinking can go over the hill faster if not properly stored. If someone is giving you a very good deal on an old red wine that you would otherwise expect to be great, start to wonder how it was kept! And a famous name on the label is no guarantee whether a wine will age well (sometimes they make mistakes, or the grapes that year ("vintage") just won't produce wines suitable for extended aging ("cellaring").
Tannin is a substance that comes from the seeds, stems and skins of grapes. (For a taste of heavy-duty tannin, try a strong cup of tea.) Additional tannin can come from the wood during barrel aging in the winery. It is an acidic preservative and is important to the long term maturing of wine. Through time, tannin (which has a bitter flavor--"mouth shattering"?) will precipitate out of the wine (becoming sediment in the bottle) and the complexity of the wine's flavor from fruit, acid and all the myriad other substances that make up the wine's character will come into greater balance. Generally, it is red wines that are the ones that can (but do not have to be) produced with a fair amount of tannin with an eye towards long term storing and maturation. The bad news is that you shouldn't drink it young since it will taste too harsh (and probably cost too much, besides). The good news is that (with a little luck) after a number of years, what you get is a prized, complex and balanced wine.
Remember that red wines get their color from the stems and skins of the grape. This gives the wine tannin and aging capacity. White wines may have no contact with the stems and skins and will have little tannin (though some can be added, again, through barrel aging). Therefore most white wines don't age well. Even the ones which do get better through time will not last nearly as long as their red cousins. A fair average for many "ageable" whites would be about 5 to 7 years (some might go 10). On the other hand, really "ageable" reds can easily be kept for 30 years and longer.
So, how do you figure out how long to keep a wine before drinking it? We'll get to a summary, but it is just a summary. Check out other sources for the particulars! The Internet provides a wonderful medium through which people who may have the wine you are thinking about drinking might already have done so. They usually are willing to share their opinions. There are several Usenet groups to this end.
Two wineries, side by side, producing the same grapes and the "same" wine. One ages considerably longer than the other. Why? While they are the "same" grapes, perhaps the soil or microclimate (small variations in the local weather due to terrain; what the French call "terroir") is just a bit different. Maybe the vines are older. The winery may have processed the wines differently (for example, heavy filtering). (In fact, even the size of the bottle matters--a half bottle ages faster than larger bottles.) There are lots of reasons, so general rules are just that--general.
In any event, the red French Beaujolais Nouveau is meant to be drunk within days. Its a light, fruity wine.
White wine is the next least aged wine. But here there is a range from a light wine like Sauvignon Blanc or a light Chardonnay, to more ageable "complex" Chardonnay of good White Burgundies. Probably drink the former within a few years (aging isn't needed, and the latter from 3 to 7 years). Dessert wines like Sauternes or other late harvest wines (Riesling, Gewurztraminer, etc.) should be aged. Sauternes get better over a very long time: 10, 20, 30, 40 or more years!
Then come the reds. While the vast majority of wines produced today can be drunk immediately, a good number of red wines will benefit by SOME aging and some will benefit from a lot of aging. The ones that you open now that taste like road tar may very well be fantastic in 5 or 10 or 20 years. Look to some French Bordeaux (maybe up to 30 years) or Cabernet Sauvignon.
Getting more specific about some red grapes, rules of thumb might be for the very best wines: Cabernet, 10 to 15 years; Merlot, 4 to 7 years for many; Nebbiolo, 10 years or more; Pinot Noir, about 5 years to start.
Some people contend that while California wine won't "go bad" in the bottle, it doesn't get any better--unlike French wines that mature (get better) with cellaring. Don't ask me to explain this controversy as I have had plenty of California wine that seemed to me to be better after aging (but then, I said I wasn't an expert. On the other hand, I know I like it when I drink it.)
So much for the summary. Didn't help much, did it? As you learn more and more about wine, you get a feel for which wines are produced to be aged. That doesn't mean that you still know when it is the best time to drink the wine. You need to check around. Ask fellow wine drinkers (and, any unbiased wine merchant with whom you can establish a relationship). Get a book that gives opinions. Read the magazines. Ask around on the 'net. These resources have the ability to tell you what happened when they drank the wine. Was it still good, is it starting to go over the hill, is it gone? At least one correspondent tells me that Australian wines seem to mature faster in Australia than in Europe, even if kept at similar temperatures and humidities. Just one more reason why it is best to ask (and taste) about individual wines.
Lucky ones (like wine critics or friends of expansive people with big cellars) can get to be part of "vertical tastings." A "vintage" is the year in which a wine is produced. Line up a particular wine on a table with a bottle from each vintage, say, 1971 through 1992 and what you get is a "vertical" of that wine. A young wine, designed to age, can taste harsh (from the tannin). As you sample older and older bottles, the wine will mellow. Flavors come into balance. The oldest wines will lose their tannin and their fruitiness and eventually have a flat taste. Somewhere in there is the vintage which tastes the way you like it. That part is up to you, not to the pundits. But their comments can help. There are lots of resources (see Learning About Wine) which can help you get an idea which wines should be drunk when.
When we first started learning about wine, we bought way too much white wine, which somehow we still have. Some of it--which was wonderful when purchased--can now best be described as awful. Since you'll hear the old cliche that you should cook only with wines you would drink, that wine isn't even good for cooking. I plan on trying to turn it into vinegar.
Aside: One of the first really "good" wines we had was a 1984 Acacia Winery Lake Chardonnay. We bought a case of it and drank it slowly (like I said, we've got a lot of white left over). A few years back we asked the winemaker how it would be. His answer was "never open it . . . just remember the way it was, you'll be happier." We're glad to say he was wrong. As this is being written, that bottle was opened last night (it was 10 years old). Past its prime but still pretty good! So even the winemaker may not always know, either.
When you are just starting out, it probably doesn't pay to buy many wines for aging ("laying down"). First off, you are going to want to drink some of them, and the ones that are "good" won't be so good this young, and they'll cost too much besides. There are plenty of wines that are good now. As you drink these wines, you'll get an idea of what types of wine you like. With a little learning, you'll get an idea of the style of wine you want to put away. And you may not make the mistakes we did, besides. (On the other hand, we did manage to get a few wines that did age well and we are just drinking now. So much for rules.)
Don't forget, how you store the wine will affect how long it lasts as well. Even the size of the bottle will change its life. Getting good advice about particular wine is the only good idea here.