"A man who has drank his drinks cold at the same expense for one week can never be presented with them warm again." -Frederic Tudor, the 19th-century "Ice King"
One of the greatest advances of the past century is something we all take for granted: the availability of ice on demand. Image what life would be like if you couldn't just open the freezer and grab a few cubes whenever you wanted. It would be like living in the Stone Age, for crying out loud! We might as well start cooking our food by rubbing two sticks together to make fire.
Ice makes almost every beverage better. That's why we drink it in water, soda, punch, lemonade, even iced tea and coffee. I've seen a few brave souls pop open a room-temperature can of Diet Coke and guzzle it down — and it makes me shudder. I can't even drink it cold out of the fridge. I need my ice.
Ice is also a crucial ingredient in most cocktails, and it's not one that should be taken too lightly. Ice plays a vital component in two ways: cooling and diluting.
Ice brings down the temperature of the drink significantly, making it taste better and more refreshing, in addition to dulling some of the sharper edges. (Our taste buds can't register the extremes of flavor in colder drinks as they can in warmer ones.)
Ice also serves to dilute the drink, softening the "fire" of the alcohol and helping the various flavors come together, while also increasing the volume of the drink.
So what kind of ice should you use? The colder and fresher, the better. Ice made in your freezer should be avoided if possible — it tends to pick up noxious odors and flavors from the leftovers you stuck in the back and forgot about three years ago. So unless you have a standalone icemaker, you probably need to buy it from the store. Once you do, keep it as cold as possible. Crank up that thermostat on your freezer until Frosty the Snowman could call it home.
Once you've got your cold, fresh ice, don't be afraid to use it. If you're building a highball, fill the glass to the top with ice. If you're mixing a cocktail, load the shaker up with cubes and shake it like you're straddling the San Andreas Fault. If you're stirring it (as with a Martini or Manhattan, which should usually be stirred), stir the drink for a good thirty seconds.
Making a quality cocktail requires using quality ingredients. Don't spoil that expensive liquor you paid so much money for by using crummy ice. Your palate will thank you.