Drink: The true spirit of Kentucky: Nicholas Faith toasts the history and differing flavours of bourbon whiskey

WHISKEY ROW they used to call it - the first block north of Third Street in the little Kentucky settlement of Bardstown. There was old Colonel Jim Beam, next to him a man called Samuel, then came Charlie Maddingly (Maddingly & Morse was once the most famous of all bourbon whiskeys) and finally Mr Harper-Bernheim of I W Harper. Opposite lived John Shawnty, who made a whiskey called Early Times.

Their neighbourliness was based on mutual respect, for they all loved and distilled good whiskey. This was natural enough, for Bardstown is in the heart of Bourbon County, a place-name that, like Cognac, is indelibly associated with a great distilled spirit. The similarity does not stop there, for the quality of the products for which both places are famous is based on limestone soil.

In Bourbon County, the limestone and the water percolating through it turn the grass blue - hence the bluegrass country. Farther west in Yellowstone, where they make Kentucky Tavern, the water is softer and less suitable for distilling. In addition, the harder Bourbon County water contains no ferrous oxide, so it produces a more pleasing colour (iron turns whiskey a blackish hue).

The grains grown in the county were also distinctive, coming from the same soil as the water. Today, however, there is not enough local grain, particularly Indian corn. This is crucial because legally, bourbon not only has to come from Kentucky but also has to contain at least 51 per cent Indian corn (maize to us). The first whiskies distilled in the 1780s by the industry's founder, the Rev Elijah Craig, were based on rye, but after Prohibition was repealed in 1933, drinkers decided that the whiskey it produced was altogether too rasping.

Today's king of the county is Bill Samuels IV, great-grandson of Colonel Beam's neighbour and distiller of Maker's Mark, the only bourbon that contains no rye at all - Samuels uses wheat. Bill Samuels' grandfather bought the Maker's Mark distillery 40 years ago for a mere dollars 67,000 ( pounds 24,000) at a bad time for bourbon.

The distilleries had been shut in 1943 to make industrial alcohol for the war effort. During the Korean war, the distillers went full blast, afraid that at any moment the government would do the same thing again. It did not, the war ended, and the distillers were left with massive stocks.

Bourbon is distilled to a mere 55 per cent alcohol, a level it shares only with armagnac, for all other spirits are distilled to a much higher level. This accounts for the fact that both spirits contain uniquely high proportions of congeners: compounds, technically known as aldehydes, which are the tasty impurities that provide spirits with their character and their drinkers with hangovers. A newly distilled bourbon has more character, more of a feel of the burnt grain, than many a mature spirit.

Bourbon is matured in barrels made out of white oak from Arkansas, not because it is inherently more suitable than other varieties but because of the power of an Arkansas congressman, Wilbur Mills, when the regulations covering the production of bourbon were being drawn up.

The barrels are charred, enhancing the richness of the congeners. If the barrels are stored just below the warehouse roof, they bake in the 100F summer heat. By contrast, barrels left in the cool depths of the warehouse, where it can be up to 60 degrees cooler, mature extremely slowly.

Most firms blend their whiskies, taking a proportion of the hot and rich from under the roof with an admixture of the cool and young from the depths of the warehouse. But Bill Samuels believes 'every barrel ought to be fully and properly matured and the only way is to rotate the barrels, leaving them in the heat to bake for only a few months one summer'. Otherwise, he feels, his whiskey would merely be a blend of 'over-age whiskies from the top and under-age from the bottom'.

But the different rate of maturation between otherwise similar whiskies means 'oldest' does not correlate with 'best'. Mr Samuels sells his whiskies at around six years old. An experimental eight- year-old whiskey was rather woody. Yet Van Winkel, the only bourbon I have ever tasted that was even richer and smoother, is four years older but does not taste woody or old because it has been less exposed to the heat.

Compared with these two, most bourbons somehow failed to impress at a recent tasting; largely, I suspect, because they had not undergone the same balanced maturation process as Maker's Mark.

Evan Williams was rather grassy, like lawnmower oil, and so, to a lesser extent, were Ten High and I W Harper. No 1 Bourbon Street (which is not a bourbon at all despite the name) was strong and rather synthetic, Old Grandad and Rebel Yell were rather spirity, Jim Beam Black Label was old and woody, while Four Roses seemed decidedly young, too reminiscent of wood shavings for my taste.

Jack Daniels? Well, that is another one that is not a bourbon; it is a Tennessee whiskey, its modern formulation due to one Len Martlow. Tennessee remained dry longer than Kentucky, and Martlow had to find a gimmick with which to relaunch the state's pride and joy. So he filtered the newly distilled whiskey (which was just like bourbon) through wood chips made of white maple.

The result was the lovely sweetness of a liquor remembered by film buffs as the one with which Humphrey Bogart wooed and won Lauren Bacall. He might, however, have been just as successful with the only other Tennessee whiskey, George Dickel, lighter than Jack Daniels but with the same seductive sweetness.