It is, after all, an afterthought - a cheap and vaguely understood though constantly present alcoholic beverage used primarily in the manufacture of martinis and other cocktails.

People may specify a certain gin in their martini but they don't request a vermouth. Of what concern is it when the gin or vodka in a cocktail is going to dominate? Yet tasting the vermouths on the market produced several revelations. First, vermouths are markedly different from each other. Second, even kept in the refrigerator, vermouth will change color and lose flavor within three or four weeks. If you don't make martinis daily, it's better to buy it in small bottles.

Third (and this was a shocker), I didn't like the taste of the Martini & Rossi Extra Dry Vermouth I consistently use at home. Vermouth is an aromatized wines, meaning the wine is infused with what are called botanicals - secret recipes of flowers, herbs, spices and roots. It is also fortified, meaning that neutral grape spirit is added to the wine to raise the alcohol level to 18 to 20 percent, from the normal 12 or 13 percent.

Such well-known aperitifs - from the Latin aperire, "to open" - as the French DuBonnet and Lillet and the Italian Campari and Cynar are specific brands of which vermouth is the general type. The bitterness that is typically an attribute of these products is designed to whet the appetite.

Steeping wine in flowers, herbs and spices believed to be medicinally beneficial is a practice going back to the ancient Greeks and Romans, who possessed a formidable pharmacopoeia of traditional natural remedies. Some of the additives the ancients used, such as chalk and tar, don't sound very attractive. The practice continued through the European Middle Ages and Renaissance. An ingredient regarded with close to universal approbation was artemesia absinthum or wormwood, thought to be effective against gastric disorders. The German word for wormwood, wermuth, eventually became the generic name for this type of wine.

Vermouth, as we know it, was invented in 1786 in the Italian city of Turin by Antonio Benedetto Carpano, assistant to a liquor shop owner. This was sweet vermouth; the dry version was created in 1800 by Joseph Noilly of Lyons, who in 1813 found a partner in Claudius Prat to market what became Noilly Prat, the world's best-selling French vermouth. However, the old and often-repeated assertion, even in contemporary drink guides, that French vermouth is dry and Italian vermouth sweet isn't true. Both countries produce sweet and dry versions, though we must remember that even vermouths labeled "Extra Dry," as all white vermouths are in the United States, contain residual sugar at about 2 percent to 4 percent, just above the detectable level.

The wine that vermouth is made from is not, it hardly needs be said, of the best variety, the base requiring little more than alcohol and a certain neutrality to serve as background for the recipes of botanicals that give vermouth what character it has. That contributes to the inexpensive nature of vermouth; most varieties sell for about $7 to $10 for a standard 750 milliliter bottle.

Here's how some vermouths I tasted stacked up against each other, rated on a four-star scale. These are all Extra Dry versions.

For years I have kept bottles of Martini & Rossi Extra Dry Vermouth, the world's top-selling brand, in the refrigerator so that I could produce martinis on demand. What a blow to discover that it smells not just smoky and toasty, but like a campfire you have just doused with water. Perhaps the smoky, damp earthen peculiarities of Martini & Rossi make it a good host for gin, but I would never drink it by itself. Rating: 1 Star.

Cinzano (cheen-ZAHN-oh) was similar to Martini & Rossi but more floral and less smoky or scorched, though that distinctive ashy quality was still present along with a little pine and moss. More pleasant than Martini & Rossi. 2 Stars.

- Made in Marseillan on the Mediterranean coast, Noilly Prat seems quite Mediterranean in a floral-herbal mode, with a luxurious bouquet of lemon peel and citron, juniper, dill and green olive and a vibrant, slightly chalky texture. A tasty before-dinner quaff. 2 Stars.

Boissiere, appropriate to its name (bois for "wood"), exudes lovely, sweet woodsy-meadowy scents with flowering grasses, dried kitchen herbs and a sweet nutty finish. A delicate and refreshing aperitif. 3 Stars.

Columns of Italian scroll down the length of the ornate Tribuno label, until at the bottom, in small letters, it says, "Made in Ripon, Cal." This is a resoundingly herbal, almost savory vermouth, whose bouquet is compounded of dry grass, lemon chive, thyme, oregano and licorice scents; it's crisp and dense in the mouth simultaneously. 2 Stars.

- The Gallo Extra Dry Vermouth has a very pretty nose of lavender, honeysuckle and jasmine, sweet grass and green olive; a touch of flint adds crispness and a welcome mineral quality to the chewy texture. 2 Stars.

The final product stands tall above the other vermouths. This is Vya, produced in Madera, Calif., by Andrew Quady, who fashions some of the state's finest ports. Vya is made from French colombard and orange muscat grapes. A vibrant pale gold color, Vya smells like anise, lavender, orange zest and thyme, and it possesses heft and personality. I would simply drink it chilled on the rocks. A superb aperitif. 4 Stars.

--Fredric Koeppel, Scripps Howard News Service