Sailing on the Silk Road, Marco Polo was one of the first Westerners to travel by sea to China. He brought back tales of tigers, paper money and the Imperial postal system, but more important, he brought back ice cream.
Or so the legend goes.
Today, the universally beloved treat occupies a $20 billion market in the United States, and Americans eat on average 20 quarts per person a year.
But this month, it's not simply a privilege to eat ice cream but a patriotic duty. Former President Ronald Reagan 20 years ago declared July as National Ice Cream Month and the third Sunday of the month as National Ice Cream Day.
Whether heeding Reagan's call or fighting hot summer days, Americans buy the most ice cream during July, and they have a wealth of ways to indulge in it. From Dippin' Dots to low-carbohydrate, low-fat, soy Popsicles to Japanese mochi (an ice cream ball rolled in a sticky rice substance), ice cream diversity may outnumber biodiversity.
Some people are choosing to return to simpler times, however, and a growing number are making their ice cream the old-fashioned way: from scratch. Most use electric ice cream makers that automatically churn the ice cream once you've added the ingredients, but the truly devoted roll up their sleeves and churn it themselves for about 30 to 45 minutes in old hand-crank machines.
"My family has been making homemade ice cream for holidays as long as I can remember," Steamboat Springs resident Shaunna Watterson said. "When I was a kid, everybody would get together for the Fourth of July, and everyone would take turns cranking. It would get down in a jiffy then."
Watterson uses her grandfather's old ice cream maker, which has a metal bowl inside a wooden container. Her favorite flavor is a lemon ice cream recipe, handed down in her family for more than 100 years.
A delicious history
Delight in frozen treats dates back much further than that, however.
In the first century, the Roman emperor Nero commanded slaves to bring him snow from the mountains, which he flavored with honey and fruit. But most historians attribute the invention of ice cream to China, and though many think Marco Polo brought it back to Europe in the 13th century, debate exists over whether that is true.
The hand-cranked churn was invented in 1846, and the first ice cream factory opened in 1851 in Maryland. At that time, large slabs of ice had to be cut from lakes in the winter and stored in large holes in the ground, making ice cream laborious to produce and a luxury enjoyed only by the wealthy.
The invention of the freezer in 1926, however, catalyzed the creation of the modern ice cream industry and the spread of ice cream to every grocery store, gas station and household refrigerator. Today, more than 90 percent of U.S. households consume ice cream, and while probably none of those households would turn down a pint of Ben and Jerry's Cherry Garcia, many are opting to make their own.
Some like the taste better, others want to avoid the preservatives in commercial ice creams and others seek the nostalgic fun of making it themselves.
"It reminds me of all our family's Fourth of July get-togethers, so I do it for the nostalgia of it, and it's darn good, too," Watterson said. "It has a really good fresh flavor, and it doesn't have preservatives, and you really can tell that."
The science behind it
Old-fashioned ice cream makers work similarly to commercial production but without all the bells and whistles. You mix cream, milk, sugar, usually vanilla extract and whatever other ingredients you desire, and then let it sit for several hours. The aging improves the whipping qualities of the mix and, hence, the final texture of the ice cream.
You then place the mix in the inner bowl of the ice cream maker. In the space between the outer and inner container you place a mixture of ice and salt, which helps freeze the ice cream.
Specifically, the salt disrupts the crystalline structure of the ice. When water freezes, the water molecules line up in an orderly pattern. The presence of salt molecules obstructs that arrangement, so the water requires more energy to line up and freeze. The water draws that heat from the surrounding environment, which, in this case, is the ice cream.
As the ice draws heat from the ice cream mixture, the ice cream freezes. So effectively, the salt lowers the freezing point of the ice allowing it to cool the ice cream much colder than it would ordinarily.
Although the ice and salt may seem like a minor component, it actually is one of the most critical factors.
"Make sure you get the ice and salt ratio right, or it won't freeze correctly," Watterson said. "Also, make sure the ice cubes aren't too big or you'll get ice cream crystals. It's smoother if the ice cubes are more chopped."
Getting the right ratio was the primary concern of ice cream novice Marge Eardley, who plans to make her first batch by herself this week.
"We'll either scoop it or drink it, I'm not sure which way it'll turn out," Eardley said.
While the ice cream is freezing, you must continuously stir the ice cream mix, so that air bubbles get trapped into the ice cream. The air is what makes the ice cream light and fluffy, and without it, the ice cream would be like an ice cube.
A lÃ¡ liquid nitrogen
Almost all ice cream production since the 1800s has used these simple physics principles, but scientists sometimes get a little fancier and use liquid nitrogen.
With this approach, you take the ice cream mixture, and while stirring it, pour an equal amount of liquid nitrogen into it. The liquid nitrogen instantly freezes the ice cream. It happens so quickly that it traps the ice cream (making it light and fluffy) and ice crystals don't have time to form (making the ice cream smooth). The liquid-nitrogen method also wins points for style because the gas from the nitrogen seethes over the bowl like from a witch's cauldron. Plus, because nitrogen is a natural component of the atmosphere, the gas doesn't pose a danger, though the very cold liquid form does.
But if, like most people, you don't have access to liquid nitrogen, you'll have to resign yourself to the electrical maker or the hand crank. The results are worth it though, Eardley said.
"It tastes way better than normal ice cream," she said.
You have to eat it quickly though, because without preservatives, the ice cream only lasts a few days, Watterson said.
"But that's never been an issue with us because everyone usually eats it all right away anyway," she said.
The other advantage to homemade ice cream is that your flavor selection is limited only by your imagination.
"After all, you can't find lemon ice cream in the store," Watterson said.