“Well of course not, it’s wet!”
It is a dreadful term, "dry". I mean who came up with the idea to use the opposite of wet to describe a wine as having no discernible sweetness? It's complete and utter gobbledegook. Should I acquire an awful thirst, the last thing I would want is something dry. (Yes that's right I have managed to use the term "gobbledegook" in a blog post. Though when its definition is "pretentious or unintelligible jargon" you would not be surprised to see its being used to describe swathes of the wine industry.) Alas it has been adopted, and it is commonly used by wine trade professionals and consumers alike.
But what does it really mean?
The simple answer would be to say it has to do with the quantity of sugar left in the wine after fermentation - the residual sugar normally quoted in g/l. Nobody can detect fewer than 2g/l of sugar in a wine, while 3-4g/l still tastes dry to most drinkers. This is not the whole story, however; if you were to think of one of the driest wines in the the world you would probably think Brut Champagne. Yet Brut Champagne can have up to 12g/l of sugar, even Extra Brut Champagne can have up to 6g/l. In this case it is the piercing acidity which is changing how your tastebuds react to the sweetness. This is also the case with New Zealand Sauvignon Blanc, where they often leave more residual sugar than, say, a French Sauvignon Blanc. Wines from New Zealand tend to have very high acidity and this makes them taste "dry". So a wine's sweetness, or dryness (pretty certain that's not a word; see it is a dreadful term), is a combination of its residual sugar and its acidity and how they interact.
How does this help me to purchase wines I am going to like?
Well probably not that much. Firstly, not every winemaker offers all the statistics on their wine, plus you are completely removing the romanticism of choosing a bottle of wine if you want to look for the residual sugar and the acidity level on the bottle. Secondly, everybody has a different palate, so a wine which tastes dry to me may taste slightly sweet to you.
So why have I read this?
Thank you if you have got this far! But what I really want you to take from this is not to be afraid of small amounts of sweetness in a wine, because even your favourite Champagne or Marlborough Sauvignon Blanc has some sweetness to it. Don't stick to grape varieties you know because they are dry, try some wonderful Rieslings (think Framingham or Beetle, both are dry) or maybe Juhfark (which has very little residual sugar but has lots of ripe fruits and honey notes) and explore the amazing world of wines, without getting too het up on the wine gibberish.