In Spanish, a margarita is a daisy. But when summer comes and daisies begin to bloom, a different kind of margarita blossoms on lawns and patios throughout the land--a fruity nectar that cools the air and warms the heart: the margarita in a glass.

A deceptively simple-sounding mixture of tequila, lime juice and orange liqueur, the liquid margarita crossed the border in the 1940s from Mexico to the United States, where variations on the basic recipe--including strawberry, peach, mango, passion fruit and everything but Fruit of the Loom margaritas--can be found in bars from coaster to coaster. It's as if the original concept of the drink became diluted as it crossed the Rio Grande.

Nowhere on this side of the border can one find a higher regard for the authentic margarita, and indeed for all things Mexican, than in San Antonio, where the Mexican and American cultures have blended as smoothly as tequila and triple sec. On a recent trip to the home of the Alamo, I decided to track down the best margarita in town.

Now, when it comes to martinis, I'm a puritanical snob. Give me good gin with a touch of vermouth and nothing else, thank you. None of those chocolate and raspberry abominations that they perpetrate in so-called martini bars. I approached my margarita quest with the same degree of closed-minded conservatism, expecting that the best margarita would be made of nothing but the choicest tequila, the freshest hand-squeezed lime juice and the finest, top shelf orange liqueur.

I could almost name the brands before I got off the plane: Cuervo 1800. Anejo tequila and Grand Marnier liqueur. All I expected to find was variations in the proportions: 3 parts tequila to 2 parts lime juice and 1 part liqueur (the usual Bartender Guide recipe) or 3 to 1 to 1, or somewhere in between. My Golden Fleece margarita would be shaken with small ice cubes, not cracked ice, and served straight up with a salted rim, not--heaven forbid--frozen.

Boy, was I in for some surprises.

I made the rounds of San Antonio's most celebrated bars, sampling two or three variations in each. (Well, someone had to do it.) Every bar had at least three kinds of margaritas on the menu, with names like the Original, La Margarita Magnifica, the Cactus Viper, Jos's Favorite and even Steve's Favorite. I was determined to find Bob's Favorite.

If I can interpret my increasingly illegible notes, here's what I learned.

The Tequila

The character of a margarita is determined most of all by the character of the tequila, and tequila comes in dozens of varieties. Some of the more popular brands are Centinela, Jose Cuervo, El Tesoro, Herradura, Patron and Sauza. Most distilleries produce several versions of the four main styles: white or silver, which is colorless and straight from the still; gold, which is colored with caramel but not aged; reposado, or "rested," in oak barrels for two to 12 months; and anejo, which is aged for more than a year.

Surprise number one: I expected that the mellower and more expensive anejos would make the best margaritas, but I found their oakiness to be too harsh for what is basically a fruity drink. Moreover, a cool margarita is most enticing when it is crystal clear, not tinged by the tannins in aged liquors.

The Juice

While many menus boast "fresh lime juice," I found that the bartenders may actually use a lime, lemon-lime or even lemon-orange-lime sweet and sour mix, made up in bulk from the fruit juices and simple syrup. Initially disappointed, I realized that a bartender can't take the time to squeeze a lime for every one of hundreds of margaritas on a busy night. The menus aren't really lying, I suppose, because the lime juice had indeed been "freshly squeezed"--at one time.

Surprise number two: Some of the sweet and sour mixes were really quite good and fresh-tasting. At home, however, I'll continue to squeeze my own lime juice.

The Liqueur

Surprise number three: I preferred margaritas made with premium triple secs to those made with either Cointreau or Grand Marnier, even though it is widely claimed that Cointreau was the liqueur of the original margarita.

In my opinion, these queens of orange-flavored liqueurs, Grand Marnier and Cointreau, do not create the best margaritas. Made from fine brandy and dried orange peel, they deserve to be sipped neat rather than be insulted with fruit juice. If their proportions in a margarita aren't carefully controlled, their bitterness and high alcohol content (80 proof) can overwhelm the flavor of the tequila, which is, of course, what margaritas are all about. Lower alcohol (30 proof to 40 proof), colorless curacaos and the refined curacaos known as triple secs perform the orange flavor duties best.

The Ice and Salt

Some people like salt around the rim of the glass, some don't. I do. A hit of salt on the tongue contrasts with the liqueur's sweetness and piques the tequila's unique flavor. The rim is dampened by rubbing it with a wedge of lime and is then dipped into a dish of kosher salt, which clings better and dissolves less easily than granulated salt.

And then there's the big question of frozen or straight up. An "up" margarita is made by vigorously shaking the ingredients with ice--either tiny cubes or coarsely cracked cubes, but never big cubes or crushed ice--and straining into a chilled glass. Frozen margaritas are blended to a slush with crushed ice.

Surprise number four: Although, as expected, I preferred the less diluted flavors of the straight-ups, some frozen margaritas, which I had previously disparaged as snow cones or Slurpees, were surprisingly good, especially in the fruitier variations. Best of all were the prickly pear cactus fruit margaritas containing the brilliant-colored pureed fruit. When one cactus (tequila's agave) meets another (the prickly pear), they envelop your taste buds in a warm Mexican abrazo (embrace).

The Proportions

There are so many kinds of tequilas, orange liqueurs and citrus sweet and sour mixes that no ratio of ingredients can possibly be quoted as "correct." It's a case of every margarita for herself. Either experiment at home with various brands and combinations or search the bars as I did, until you meet your margarita.

And what was Bob's Favorite? There were four finalists. "The Traditional" and "Steve's Favorite" at La Fonda, The "Sauza Commemorative" at the Canyon Cafe, and the overall winner for best combination of flavor and beauty--may I have the envelope, please--the forthrightly named "Prickly Pear Margarita" at the Zuni Grill.

I stayed away from one well-known San Antonio restaurant where, according to my bartender confidants, they spike the margaritas with extra grain alcohol. And I politely declined the offer of a 40-ounce (more than a quart!) margarita at Polo's Restaurant in the Fairmount Hotel.

After all, I had work to do.

Bob's Favorite At-Home Margarita

(2 servings)

Salt on the rim of a margarita glass should be on the outside only, so it doesn't fall into the drink.

Kosher salt

1 ounce freshly squeezed lime juice, plus additional for the glass

3 ounces Cuervo Especial tequila

1 ounce Hiram Walker triple sec

Small ice cubes or cracked (not crushed) ice

Place the salt in a wide, shallow dish. To coat the rim of a glass, dip a finger in the additional lime juice and wet the outside portion of the rim of each martini glass. Roll the wet rim of each glass in the salt, leaving a deposit on the outside edge only, not the inner rim. Place the glasses in the freezer until ready to mix the drinks.

Pour the remaining 1 ounce of lime juice, tequila and triple sec into a cocktail shaker. Add the ice and shake vigorously for 15 seconds. Strain into the chilled glasses and serve.

Per serving: 141 calories, trace protein, 6 gm carbohydrates, trace fat, 0 mg cholesterol, trace saturated fat, 233 mg sodium, trace dietary fiber

Margarita Pie

(8 servings)

You'll think you're eating a margarita.

Nonstick cooking spray

For the pie shell:

5 ounces pretzels (about 1 cup crushed pretzel crumbs) plus extra for garnish

1/4 cup sugar

6 tablespoons butter, melted

For the filling:

1 envelope plain gelatin, less 1/2 teaspoon

2/3 cup fresh lime juice (from about 6 limes)

4 large eggs, separated

1 cup sugar

1/4 teaspoon salt

1 teaspoon lime zest

1/3 cup tequila

3 tablespoons triple sec

Kosher salt

Lime wedges

Spray an 8 1/2-inch springform pan with the nonstick cooking spray.

For the crust: Place the pretzels in a plastic bag and crush with a rolling pin. (The crumbs should be coarse, so do not use a food processor or blender.) Combine the crumbs, sugar and butter. Press the mixture into the bottom of the prepared pan and about 1 inch up the side.

In a small wide bowl, sprinkle the gelatin over the lime juice. Set aside. Fill a large bowl 2/3 full of ice cubes and cold water. Set aside.

In the top of a double boiler over simmering water, combine the egg yolks, 1/2 cup of the sugar, the salt and lime zest. Add the softened gelatin-lime juice mixture and cook, stirring constantly, until the mixture is slightly thickened and the gelatin is completely dissolved, about 5 minutes. Remove from the heat and stir in the tequila and triple sec.

Transfer the top of the double boiler containing the lime mixture to the large bowl of ice water. Stir the filling occasionally until the mixture is cold but not thickened, about 5 minutes.

Beat the egg whites with the remaining 1/2 cup sugar and continue beating until the whites hold soft shiny peaks. Whisk 1/3 of the egg white mixture into the lime mixture. Switching to a spatula, gently fold in another 1/3 of the egg whites, bringing the mixture from the bottom up and over the top. Then fold in the remaining 1/3 of the egg whites. Allow the mixture to remain in the pan set over the ice water for 5 minutes, folding gently occasionally. It will set slightly.

Pour the mixture into the crust and chill until set, about 6 hours or overnight.

Run the tip of a sharp knife around the edge to loosen the pie before removing the outside ring. Pass kosher salt, lime wedges and pretzel crumbs to sprinkle on top.

Per serving: 320 calories, 5 gm protein, 42 gm carbohydrates, 12 gm fat, 131 mg cholesterol, 7 gm saturated fat, 299 mg sodium, trace dietary fiber

Robert L. Wolke is professor emeritus of chemistry at the University of Pittsburgh and the author of "What Einstein Didn't Know--Scientific Answers to Everyday Questions."