AS HE swallows a modest sip of wine, Alexander McCall Smith furrows his brow in concentration. "What does that taste of, Will?" he asks. "Stewed fruit – baked cherries, perhaps," I volunteer. "Yes, that's it: dark cherry jam, the sort my grandmother used to make."

It is not unpleasant, but neither is it what we were expecting. We're having lunch in the kitchen of Sandy's Victorian house in Edinburgh: soup, bread and crayfish. Beforehand, he'd let me rummage around his cellar, in effect a small corridor filled with a handful of cases acquired during a recent trip to Bordeaux.

There is no room for ostentation here – rather like his No 1 Ladies' Detective Agency series, it's a charming, modest, uncomplicated collection.

Sandy's first love is Brunello di Montalcino, made in the lush valleys of Tuscany, but a bottle of 1997 Château La Croix Canon catches my eye. As each of us has writing commitments ahead, we agree to have just one glass.

Château La Croix Canon lies in Canon Fronsac, a small, hugely underrated appellation to the north of Bordeaux. Here, merlot thrives on the high limestone and sandstone soil. When they're young, these wines can have a biting, spicy intensity, but any lack of suppleness is compensated for by price, which is always very competitive. We take another sip.

"What's happened to it?" asks Sandy. The wine tastes a little volatile. The acids are masking the fruit, and the tannins – those bitter-tasting compounds found in the stems, seeds and skins – are very faint, giving the wine a watery feel. Maybe it's past its best, I suggest, before correcting myself – for claret, 1997 isn't that old.

Fine wines are made in such a way that they benefit from bottle-ageing. When the grapes are picked, the winemaker extracts plenty of acid, tannin and flavour compounds, such as sugar.

Tasted young, the wine can appear unattractive – almost undrinkable, in some cases – but with time the tannins subside, the acid mellows and the fruit re-emerges with a deeper, more complex character. The key to bottle-ageing is knowing when all three factors come together at the same moment. Pull the cork too soon and the fruit may still be lying dormant, masked by the youthful tannins. Left for too long, the fruit could disappear altogether and the acidity can lose its sharpness. This leaves the wine tasting flat or flabby.

The effects of ageing can be simulated by exposing the wine to air – pulling the cork and pouring into a decanter. Once in the glass, the oxygen from the air dissolves into the wine, reacting with the phenolic compounds. With Château La Croix Canon, the reaction with the oxygen had reduced the acid and the tannins, mellowing the taste. Meanwhile, the reductive flavours of stewed fruit had blown off. On the third sip, after the wine had spent about half an hour in the glass, we both concluded it really did taste quite nice.

2008 McGuigan Discover, Pinot Grigio, Australia, 13.5%, £5.99

Crisp, clean and zippy. Pop this in the fridge and serve as an aperitif. With an attractive citrus kick, it's very moreish. Tesco

2005/06 Château Liversan Haut-Médoc, Bordeaux, France, 13%, £10.44

A hugely rewarding, reliable claret that is packed with ripe blackberry and autumnal notes of fruit. Long and succulent on the palate, this will not disappoint. Waitrose

2006 Chianti DOCG, Piccini, Italy, 12.5% £5.99

A first impression throws up a spicy, peppery wine that seems a little overpowering. The distinctive bitter flavour that is common with some Italian reds soon disappears, leaving unctuous, voluptuous

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