The hard shell topping on an ice cream cone hardens for one of two reasons: paraffin wax or coconut oil. Both of these ingredients become soft or liquid when warm, but solidify quickly when exposed to cold ice cream. When combined with chocolate or another flavor, they allow the topping to completely cover the scoop of ice cream on top of the cone, adding a tasty, protective outer layer.
Paraffin Wax
The paraffin wax used in some recipes for hard shell topping is a food-grade wax, meaning that it's safe to eat. Edible paraffin cannot be absorbed by the body, so it simply passes through. This wax has no taste, and melts at relatively low temperatures — between 116°F (47°C) and 149°F (65°C). It is found in some candies, chocolates, and even on the outsides of some fruits and vegetables to make them shiny.
Coconut Oil
Coconut oil contains high amounts of saturated fat, which are solid at room temperature. It melts at an even lower temperature than paraffin — just 74°F (23.3°C) — making it a very popular choice for bottled hard shell topping sold for home use. This oil freezes and solidifies very quickly when exposed to freezing temperatures, such as from ice cream. Coconut oil is naturally sweet and light; although refined oil loses most of its flavor, unrefined oil has been described as having a rich, nutty taste. Because coconut oil is digested by the body, toppings made with it will contain more fat and calories than those made with wax.
Topping Flavors
Although many hard shell toppings are flavored with chocolate, this is not the only type available. Many different flavors can be mixed with wax or oil, including vanilla, caramel, cherry, and orange creme. Chocolate-based variations are also very popular, with peanut butter, cherry, s'mores, and toffee as common additions.
Making Hard Shell Topping
Most toppings bought at ice cream parlors or in a bottle are made with just a few ingredients, including the chocolate or other flavorings, sugar, sunflower or other oil, and paraffin wax or coconut oil. Recipes for homemade hard shell topping are usually even simpler, and include just the coconut oil and flavoring; most flavorings, like chocolate chips or raspberry syrup, already contain a lot of sugar, so more is rarely needed. Homemade recipes usually do not contain paraffin wax, because food-grade wax can be difficult to find and coconut oil is easier to work with. Regular paraffin wax can contain impurities that may be toxic, and wax that is not specifically labeled as being safe to eat should not be used.