When it comes to wine, vintage is the big one, the thing most people tend to find complicated and confusing. But the bottom line is that it's all actually quite simple. A wine's vintage simply tells you which year the grapes were picked.

Almost all still wines come from a single vintage, and the labels on the bottles will show the year in which the wine was made. The few exceptions to this rule are a few cheap and barely drinkable wines, or branded wines, such as Piat D'Or or Blue Nun.

Fortified and sparkling wines, including Champagne, tend to be non-vintage, however. This is because they are frequently created from a blend of different vintages, with the aim of creating a consistent 'house style'. The exception to this particular rule, however, is that, in an outstanding year, Vintage Champagne and Vintage Port will be made.

In both cases, it is down to the producer to decide whether a year is sufficiently good to produce a single vintage wine. Port is matured in oak barrels for two years before it is assessed to determine its quality – only then will the decision be made as to whether a vintage will be declared. The conditions have to be just right to produce grapes of a sufficiently high quality to make Vintage Champagne – as a rule, this means that there are usually only about four or five such vintages in a decade.

But why should one vintage be any different from another? The answer lies in the weather. The micro-climate of any particular wine-growing region varies, sometimes quite dramatically, from one year to the next. Different grape varieties respond to different climatic conditions in their own particular way. On the whole, for instance, Syrah/Shiraz responds particular well to dry, sunny conditions that favour the ripening of its sugars, a key ingredient of its heady, alcoholic kick – that's why growers in South Australia's Barossa Valley have been particularly successful in producing wines made from this grape. On the other hand, Sauvignon Blanc responds well to somewhat cooler, damper conditions, which is why it thrives in the Loire Valley and New Zealand's South Island.

Poor weather conditions – those that are not appropriate for whatever grape variety is being grown – are the true test of a good producer, for it is his (or her) knowledge and experience, through manipulation of the vinification process and skilfull blending, that extracts the best possible performance from the grapes. It is said that a great winemaker can create a good wine from poor grapes; but a mediocre winemaker will only make an average wine, even he has if a harvest of perfect grapes.

But even the most superior of winemakers is sometimes tested by the elements. The El Niño cycle, whose effect is particularly strong in Australia, can result in unpredictable weather patterns, with attendant complications for the area's wine producers. Heavy rains in 1993 resulted in a disastrous vintage of light wines; two years later, in 1995, drought conditions led to very low yields indeed, although the grapes did ripen well. Luckily, the weather sometimes works in Australia's favour – the long, warm summer of 1998 gave rise to an exceptional vintage.