Summer wines are a category unto themselves. And what, exactly, is a summer wine? To borrow from former Supreme Court Justice Potter Stewart’s famous line about obscenity, you know a summer wine when you taste it. Still, certain criteria do exist. A summer wine is always served cool. And somehow, it’s never an “important” wine, whatever that is. (See Justice Stewart.) Most summer wines are inexpensive, reflecting the relaxation of the season. Most importantly, a good summer wine refreshes. And it lends itself to what might be called sunset-sipping, which means that it stands on its own.

The following “summer wines” deliciously fulfill all these criteria and pass the Justice Stewart test with consummate ease.

DR. L RIESLING 2004, ERNST LOOSEN

Almost no one would dispute that Germany’s Mosel-Saar-Ruwer region creates the world’s most delightful rieslings. They are summer wines supreme. Yet too often, buying these wines can seem daunting.

Part of the problem is the sheer complication of the zone, which is divided into hundreds, even thousands, of named vineyards. Then there’s the complication of varying grades of sweetness levels, specified from the driest (trocken) to the sweetest (trockenbeerenauslese), with five stops in between. Finally, there’s the dizzying number of individual growers.

All of this serves to steer folks from German rieslings to the one-size-fits-all simplicity of, say, chardonnay. This is a great loss, not just for German winegrowers but above all, for wine lovers everywhere. German rieslings are simply some of the world’s greatest white wines.

Happily, one of Germany’s finest winegrowers, Ernst Loosen, is making matters simpler – as well as invitingly inexpensive. Mr. Loosen, who owns choice parcels in the best part of the Mosel Valley, knows that many of his neighbors grow fine riesling grapes, but they sell them to local growers’ cooperatives, where they get blended with lesser stuff.

So Mr. Loosen set out to use his insider knowledge, powered by his own high standards, to create an everyday German riesling from the Mosel that is dramatically different from anything else on the market. He succeeded. He calls the wine Dr. L and the latest vintage (2004) is succulent stuff indeed.

Low in alcohol (only 8.5%), this is delicious Mosel riesling. It’s slightly sweet with brisk, but not teeth-shuddering, acidity. This acidity makes it refreshing to drink, balancing the slight sweetness. As for taste, imagine the most delicate, savory, ripe-yet-brisk Granny Smith apple and you’ll be close. Add a faint mineral savor while you’re at it.

One more thing: Dr. L is beautifully packaged. The label is elegant and simple. The riesling name is boldly, proudly declared in curving script. And it’s got a screw cap, the better to preserve the pristine flavors of the wine. Not least, the price is superb: $9.95. I’d be amazed if, after one taste, you don’t decide to lay in a case or two of this wine and declare it your house summer wine. It’s that good.

MOSCATO D’ASTI 2004, SARACCO

If there’s a greater warm weather wine than Piedmont’s Moscato d’Asti, then I haven’t tasted it. And if you haven’t tasted a Moscato d’Asti, I can’t urge you too strongly to redress this, pronto.

Chances are you’ve tasted – and enjoyed – its more famous cousin, Asti Spumante. It, too, is made from the moscato bianco grape variety. But the connoisseur’s choice is the much rarer, more artisanal bottling called moscato d’Asti.

The story here is that although moscato bianco grows in many parts of Italy, nowhere does it grow better, with greater refinement and finesse, than the steep, chalky clay slopes of the Piedmont region in northwestern Italy. There the grape achieves perfect acidity while acquiring equally perfect, but not excessive, ripeness. What results is a moderately sweet wine with invigorating acidity allied to unusually low (5.5%) alcohol. It’s tremendously refreshing stuff.

This was not lost on the big wine companies of the zone. So they created a fully foaming (spumante) version of moscato bianco called Asti Spumante, named after the major wine town of the zone. Making Asti Spumante requires specialized equipment.

But the little growers of the area had neither the capital nor the interest to acquire such expensive equipment to make a fully sparkling moscato. So they made their own version for their private consumption that was bubbling but not foaming, what the Italians call frizzante. This is moscato d’Asti.

Precisely because moscato d’Asti is almost always a small-production, grower-created wine, the quality level is much higher than the more industrial Asti Spumante. It’s what the local Barolo and Barbaresco producers themselves drink. (I lived in Piedmont for a year and never once saw them drink Asti Spumante, but they dote on moscato d’Asti.)

The best producer of moscato d’Asti, for this taster, anyway, is Paolo Saracco. He specializes in making this wine, and although Mr. Saracco has worthy competitors, no one issues a richer, fuller, more dimensional moscato d’Asti.

This is a summer wine supreme. Moscato d’Asti is meant to be drunk as young and fresh as possible, as well as bracingly cool. This just-off-the-boat 2004 bottling is a fine moscato vintage displaying the finesse and nuance that set moscato d’Asti apart from all others. It’s best served as an aperitif or with dessert, alongside cookies, pound cake, and, not least, a glowing sunset. The alcohol is as low as any wine you’ll ever drink, so you can keep sipping with gluttonous pleasure. $14.95.