Published July 1, 2011. From Cook's Illustrated.
The quicker it freezes, the smoother the ice cream, so we sped up the freezing time of our homemade Vanilla Ice Cream recipe by starting with a colder base. Supplementing the sugar with corn syrup gave us a Vanilla Ice Cream recipe that produced ice cream that froze faster, remained hard at home-freezer temperatures, and was devoid of large ice crystals.
Two teaspoons of vanilla extract can be substituted for the vanilla bean; stir the extract into the cold custard in step 3. An instant-read thermometer is critical for the best results. Using a prechilled metal baking pan and working quickly in step 4 will help prevent melting and refreezing of the ice cream and will speed the hardening process. If using a canister-style ice-cream machine, be sure to freeze the empty canister at least 24 hours and preferably 48 hours before churning. For self-refrigerating ice-cream machines, prechill the canister by running the machine for 5 to 10 minutes before pouring in the custard.
Getting to Yes
Creating smooth ice cream means cutting back on ice crystals, or preventing them from forming in the first place. We tried a slew of ingredients promising to do just that, most with unfortunate side effects.
Condensed and evaporated milk contribute less water to the mix, leading to fewer ice crystals. But ice cream made from each tasted “cooked.”
Cornstarch traps water so it can't form ice crystals, but it produced a "weird", "gummy" texture. Gelatin and pectin bombed, too.
Nonfat dry milk ups the overall milk solids in the custard base, thus blocking ice crystal formation, but it left a "cheesy" flavor.
Some granulated sugar plus corn syrup, which also interferes with crystal formation, made for a super-smooth texture- with no funky side effects.
Combating Iciness with Corn Syrup
One key to our ice cream's smoothness was to replace some of the sugar with corn syrup. This sweetener has a twofold effect: First, it is made up of glucose molecules and large tangled chains of starch that interupt the flow of water molecules in a custard base. Since the water molecules can't move freely, they are less likely to combine and form large crystals as the ice cream freezes. Second, corn syrup creates a higher freezing point in ice cream than granulated sugar does. This makes the ice cream less susceptible to the temperature shifts inevitable in a home freezer. These shifts cause constant thawing and refreezing, which creates crystallization even in the smoothest ice cream. Our ice cream stayed smooth for nearly a week- far longer than most homemde ice creams do.
For Super-Premium Smoothness, Keep It Cold
Freezing the custard as quickly as possible ensures the formation of small (versus large) ice crystals that re critical to smooth ice cream. Commercial producers use blast freezers or hardening rooms, where the temperature can hover as low as -50 degrees. We resorted to far humbler methods—with suprisingly similar results.