We like our wine to be dry, don’t we? Unless, of course, it is unashamedly very sweet (and even this, alas, is a minority taste). But the supposedly dry wines on our shelves can vary substantially in how much unfermented sugar they contain – and those that fall between dry and sweet present real challenges.

Sweetness in wine, known as “residual sugar” or RS, is usually measured in grams per litre of liquid, although Americans generally express it as a percentage. It is impossible to get RS levels down to zero (wine starts out as very sweet grape juice) but the general threshold of perception of sweetness is around 2g/l (or 0.2 per cent). Most fine red wine is well below this, often less than 1g/l, so doesn’t taste at all sweet.

It’s a different story with mass-market brands. Yellow Tail, the archetypal “critter” brand so successful it now accounts for almost half of all Australian wine imported into the US, is famously relatively sweet – as is one of the most successful brands of California Chardonnay, Kendall Jackson Vintner’s Reserve. These brands are likely to notch up sugar levels of at least 5-6g/l. Some of the California whites naughtily labelled Chablis, even though it is a controlled geographical appellation in Europe, can notch up well over 10g/l of sugar, often in the form of deliberately added sweet grape juice concentrate.

Those who routinely analyse wine report that, in general, inexpensive products – reds as well as whites and pinks, made in California, Australia, Chile and New Zealand – have notably higher sugar levels than Europe’s “dry” wines: 3-8g/l rather than 1-2g/l. Because of New Zealand’s relatively high latitudes, acid levels in the grapes tend to be higher than in wine regions closer to the equator. The higher the acid, the less sweet a wine tastes, so Kiwi wines’ sweetness tends to be less obvious than those grown in hotter climes.

Sweetness can be used deliberately by a winemaker to counteract excessively high acidity. Some of France’s cheapest “dry” white labelled Vin de Pays des C?tes de Gascogne from armagnac country, for example, tends to be extremely high in acidity, so winemakers often soften this by boosting the natural sugar level. This technique may be applied to some commercial whites from Italy where high yields leave the grapes very high in acid. European reds that are sold as dry but often in fact contain up to 8g/l of residual sugar include some of the less artisan wines from Sicily and Puglia in southern Italy.

Another factor that can affect how sweet a wine tastes is temperature. At a recent blind tasting, we were, unbeknown to us, served the same wine twice, once at room temperature and once well chilled. We all thought the chilled version of this sweetish wine (60g/l residual sugar) was drier than the warmer one because acidity is more prominent at lower temperatures.

Although virtually all red wines are relatively dry, the level of residual sugar in white wines can vary enormously – from under 2g/l to hundreds of grams per litre in naturally sweet wines made from really ripe grapes. Wines at each end of the sweetness spectrum are generally easy to identify and we more or less know how they are going to taste. But a considerable proportion of white wines lie somewhere in between dry and very sweet. It can be very frustrating to buy a bottle of wine and find that it is much sweeter (or drier) than expected. The wines of Alsace have been particular sinners in this respect. They can vary from bone dry to medium sweet without any indication on the label to help the consumer. This has driven a handful of producers such as Zind Humbrecht to devise their own systems for indicating sweetness.

In the US, where Riesling has had a head of steam behind it (largely thanks to Washington state’s Chateau Ste Michelle and its joint venture with Erni Loosen of Germany’s Mosel Valley), an American-based organisation called the International Riesling Foundation has also come up with a graphic to be used on wine labels to show the degree of sweetness.

It was to test how well this scale, the Riesling Taste Profile, from dry through gradations of medium dry and medium sweet to sweet, could be applied to a wide, international range of Rieslings that 25 of us tried to grade the sweetness levels of 26 examples ranging in sweetness from 0.92 to 207.50g/l. We were shown International Riesling Foundation guidelines of extreme complexity beforehand that indicated what influence acidity and the level of pH (the intensity of the acidity), should have in addition to the residual sugar level. One of the tasters was Wendy Stuckey, responsible for Chateau Ste Michelle’s highly successful Washington state Rieslings. She confessed that, when deciding exactly which point on the Riesling Taste Profile should be applied to each wine, they took no notice of the formulae and did it all on how it tasted.

I’m not sure average consumers can be bothered with comparing nuances of gradation. They probably just want to know whether a wine is dry, medium dry, medium sweet or sweet – and many consumers will already be prejudiced against any wine not in the first category. This is a great shame since many delicious fine white wines taste a little sweet, though, thanks to counterbalancing acidity, are far from cloying. I have listed some of my favourites on page 37.

The only trouble with medium dry and medium sweet wines is working out how to serve them. If, like a German Kabinett and Sp?tlese, they are low in alcohol, they may well be too light to stand up to anything other than the most neutral white fish dish and are best drunk on their own. But whites such as the richer examples from Austria and Alsace, medium dry Chenins made in the image of Vouvray and Tokaji have quite enough body to accompany food and can be delicious with rich shellfish, creamily sauced savoury dishes and smooth patés.