For a wine to give out a distinctive flavour or character is normally seen as a plus. Not in the case of wines from the Cape. The talking point in South African wine right now is an unpleasant off-odour and taste in some bottles – described variously as burnt rubber, rhubarb or sun-dried tomato. No one knows what it is, but you know it when you see, or rather, smell and taste, it.

The topic may be hot, but it's hardly new. When a group of British Masters of Wine visited the Cape way back in 1976, they described pinotage, South Africa's own red grape variety, as smelling of "rusty nails". It set the pinotage cause back by years. Today's off-odour may well be similar to the "rusty nails" taint that was ascribed by some to the virus problems that have afflicted South African vineyards over the years, and by others, such as the late wine writer David Wolfe, as a "taste of apartheid".

It was with limited expectations, then, that I spent a May Sunday afternoon before this year's annual Trophy Wine Show in the Cape tasting 27 mature South African wines from vintages between 1983 and 1940, all procured by the show's chairman, Michael Fridjhon. Some, like the 1982 Rustenberg, the 1974 Nederburg Auction Cabernet, 1969 Zonnebloem Cabernet and the 1966 G S Cabernet Sauvignon, rivalled top Bordeaux reds for complexity and longevity. Others were starting to dry out. Yet there was not even the faintest whiff of that unpleasant taint.

None the less, the South African wine industry is aware there is a problem, even if it's not very good at detecting it. For that reason, a panel of tasters was assembled in London last month to look at the issue – their findings are being analysed to try to get to the bottom of it. Watch this space. Meanwhile, as the Trophy Show got under way, I judged an impressive line-up of sauvignons, sweet white and red muscats, vintage and tawny "ports", and a range of Bordeaux-style blends and merlots. Some of the red blends showed real quality. Others displayed faults relating to poor winemaking, cork taint and vineyard issues of stress-related greenness and heat-related jammy portiness. Yet in only one wine did I come across that unmistakeably yucky "it-could-only-be-South-African" pong.

I feel that the issue of taint is relatively minor compared with the other cellar and vineyard problems of the Cape. The 1970s were a particularly bad time for viruses in South Africa's vineyards, but it looks as if the problem doesn't lie in virus-affected vines alone.

But let's not overlook the positives in South African wine. Not much more than a decade ago, the wine industry was more or less confined to the "golden triangle" of Stellenbosch, Franschhoek and Paarl, while today's producers are more adventurously "New World". It's heartwarming to see that a new generation of savvy winemakers has expanded the frontiers of wine to select the right match between location and grape variety.

The furore over the reds has also obscured the fact that, after a long and elusive search involving shiraz and Rhone-style blends, South African wine producers have begun to put their fingers on a valid new style to compete with Bordeaux-based blends.

In a relatively short timespan, they have discovered, too, an ability to make distinctive sauvignons, semillons, chardonnays and chenin blancs in a variety of styles that don't ape the Loire, Bordeaux, Burgundy or New Zealand (and that are also good value).

I will aim to return to the subject of some of South Africa's top wines after the Trophy Show results are announced next month.

Wine: Something for the Weekend?

Under a Fiver

2007 Tesco Chilean Reserva Cabernet Sauvignon

From Cono Sur, one of Chile's most appealing brands, this lightly minty cabernet sauvignon with its soft, opulent fruit, suggests what good claret under a fiver might be like.

£4.69, Tesco

Under a Tenner

2007 Wither Hills Pinot Gris Marlborough, New Zealand

New Zealand is increasingly coming up with impressively ripe and spicy wines, such as this refreshingly juicy, apple and pear-flavoured dry white.

£9.99, Waitrose

Splash Out

2005 Cuvée Occitane Rouge, Domaine Gayda, Vin de Pays d'Oc

This "fruit salad" Mediterranean of syrah and grenache displays a berry fruitiness and a sleek veneer of spicy oak.

Around £10.99, Bona Wines, Tetbury (01666 505911)